Thursday, 9 March

Evolution of the 30 June 2014 Double Derecho Event in Northern Illinois and Northwest Indiana

Matthew T. Friedlein, Richard Castro, and Eric Lenning, NOAA/NWS Chicago, IL

Anthony W. Lyza and Kevin R. Knupp, Severe Weather Institute - Radar and Lightning

Laboratories, University of Alabama in Huntsville (UAH-SWIRLL)

In a seven hour period on the evening of 30 June 2014, two separate quasi-linear convective systems (QLCSs) exhibited derecho characteristics as they tracked across northern Illinois. As the first derecho gradually waned and moved northeast, the second derecho intensified behind it and progressed southeast. Both organized storm complexes resulted in widespread wind damage, gusts of 26-35 m/s (58-80 mph) or higher, sporadic reports of large hail, and areas of flooding. The second derecho also was responsible for 29 documented tornadoes across northern Illinois and northern Indiana. While the late spring and early summer period is favored for QLCS events in the Corn Belt states, the rapid succession of these two organized convective features with the latter being more pronounced made this event especially noteworthy.

This presentation will explore the synoptic and mesoscale processes that contributed to this unusual event. Many of the environmental variables linked to derechos were present, however, there was a noteworthy change in mesoscale elements within the two hours between the derechos. These key factors include a limited cold pool imprint from the first derecho, strengthening of a surface theta-e boundary, more pronounced deep layer shear, and greatly enhanced storm relative helicity. The stronger dynamics in the presence of only slightly elevated instability favored persistent storm-scale characteristics and interactions that are more conducive for tornado development within the second derecho.

Shown in this presentation will be environmental attributes and their evolution ahead of and during the derechos through surface observations, vertical wind profiler data, modified local ACARS soundings, and SPC RAP mesoanalysis. The role of the surface theta-e boundary and its enhancement from the outflow of the first derecho also will be discussed.

Storm Scale Meteorological Processes in the 30 June 2014 Double Derecho Event

Eric Lenning, Richard Castro, and Matthew T. Friedlein, NOAA/NWS Chicago, IL

Anthony W. Lyza and Kevin R. Knupp, Severe Weather Institute - Radar and Lightning

Laboratories, University of Alabama in Huntsville (UAH-SWIRLL)

An unusual evolution of a pair of quasi-linear convective systems was observed during the evening hours of 30 June 2014. The first QLCS manifested as a progressive derecho, with numerous high-end wind damage reports across Iowa and northern Illinois. As the first QLCS began to weaken, a second QLCS formed over central and eastern Iowa. This one also exhibited derecho characteristics as it propagated quickly across northern Illinois and northern Indiana before weakening in northwestern Ohio.

While the development of a secondary QLCS certainly is not unusual, the severity of the second QLCS in this case was uncommon. The second QLCS was particularly damaging, with numerous instances of 35-45 m/s (80-100 MPH) estimated straight-line wind gusts and at least 29 tornadoes, all rated EF0-EF1. The passage of the second QLCS through a relatively dense surface observational network and good radar coverage allowed for several noteworthy observations. These observations include:

The bore-driven nature of the second QLCS for its entire lifecycle, with numerous clear bore-apparent surface observation traces and system forward motion substantially greater than that supported by its associated buoyancy deficit or mean tropospheric flow;

Apparent wave interactions with the QLCS, including one particular interaction that was spatially and temporally associated with mesovortex genesis and quickly followed by formation of an EF1 tornado;

A remarkable detection of a tornado within 10 km of the Chicago-Romeoville NEXRAD radar (KLOT), which detected a maximum wind speed of approximately 66 m/s (128 kt or 147 MPH) at an elevation of approximately 230-235 m (755-775 ft.) AGL; and

Growth and intensification of a mesovortex upon interacting with a remnant thermal boundary from the first derecho-producing QLCS. This mesovortex veered to propagate along the boundary, eventually split into two subvortices, and produced a remarkable flurry of at least 14 confirmed tornadoes, along with areas of widespread wind damage estimated to be caused by winds of at least 45-50 m/s (100-110 MPH).

This presentation provides a detailed review of these observations and examines the role of mesoscale and especially storm-scale interactions that contributed to the severity of the second QLCS, and particularly its tornadic nature. It also discusses how these observations raise additional questions to be addressed through further research into this case and others.

Observations of Complex Mesovortex Interactions and Behaviors during the Second 30 June - 1 July 2014 Midwestern Derecho Event

Anthony W. Lyza, Adam W. Clayton, and Kevin R. Knupp, Severe Weather Institute -Radar and Lightning

Laboratories, University of Alabama in Huntsville (UAH-SWIRLL)

Eric Lenning, Matthew T. Friedlein, and Richard Castro, NOAA/NWS Chicago, IL

Evan Bentley, NOAA/NWS Portland, OR

A pair of intense, derecho-producing quasi-linear convective systems (QLCSs) impacted Iowa, northern Illinois, northern Indiana, and southern Lower Michigan from the late morning hours of 30 June through the pre-dawn hours of 1 July 2014. As the first derecho weakened across northern Indiana and southern Lower Michigan, a secondary QLCS formed across central and eastern Iowa in its wake. This secondary QLCS produced 29 confirmed tornado tracks and numerous instances of 80-100 MPH straight-line wind damage. Many of these mesovortices occurred within close proximity of the Chicago (KLOT) and Northern Indiana (KIWX) Weather Surveillance Radar-88 Doppler (WSR-88D) sites and the terminal Doppler weather radar (TDWR) located at Chicago-Midway International Airport (TMDW). The close proximity of the mesovortices to these radar sites afforded numerous unique radar observations of mesovortex behavior and interaction, including:

1. A binary (Fujiwhara) interaction between two mesovortices, sampled with 1-minute TDWR resolution;
2. The intensification, growth, and splitting of a large mesovortex into two subvortices along a thermal boundary and subsequent prolific tornado occurrence;
3. Trochoidal oscillations in mesovortex translation;
4. A row of tightly-spaced mesovortices, each associated with a tornado debris signature (TDS), and merging of the TDSs into a larger cloud of tornado debris;
5. Three satellite mesovortices rotating around a larger parent mesovortex; and
6. Mesovortices forming within a convective band immediately ahead of the primary QLCS.

This presentation showcases radar observations of these behaviors. We place these observations in the context of past work completed on radar observations of QLCS mesovortices and the dynamics of mesovortex generation. Research and operational questions related to these observations are addressed.

The Northern Illinois/Indiana QLCS Tornadoes of 30 June 2014

Todd Holsten, Jeff Logsdon, and Evan Bentley, NOAA/NWS Northern Indiana

Kyle Brown, Valparaiso University

On the night of June 30/July 1, 2014, two separate quasilinear convective systems (QLCS’s) tracked across the southern great lakes region. This event had a complex evolution as thunderstorms developed across Iowa during the early afternoon of June 30th. The storms organized into a forward propagating QLCS and tracked east-¬northeast toward Lake Michigan by early evening. The lead portion of this system split and lifted northeast while southwestern flank reorganized, yet quickly outran better shear and became outflow dominant before dissipating over northwest Indiana. This left behind a pronounced southwest¬-northeast oriented outflow boundary across eastern Illinois and northern Indiana. New convective storms rapidly developed and intensified further west along a prefrontal trough in eastern Iowa and northwestern Illinois and organized into a second QLCS. This second system, aided by an enhanced mesoscale environment, became a prolific tornado producing QLCS as it accelerated eastward and moved through northeast Illinois and northern Indiana. This presentation will examine some of the mesoscale processes and storm-scale evolution during this event as well as radar interrogation and warning decision making considerations, including application of research techniques to operations.

Effective Hazards Communication: Motivating Protective Action in Advance of Severe QLCS Events

Daniel Hawblitzel, NOAA/NWS Kansas City/Pleasant Hill, MO

Quasilinear convective systems can pose significant threats to public safety including strong tornadoes, widespread severe winds and life-threatening flooding. In many cases these tornadoes may occur with little to no lead time, which presents significant vulnerability to those who need longer warning lead times such as hospitals, large events and mobile home residents. Conventional methods of communicating severe thunderstorm forecasts, which focus mostly on anticipated coverage and magnitude of severe weather, may not adequately convey the unique threats posed by severe QLCS events particularly to those who are most vulnerable. To ensure protective action is taken by those most at risk, users must understand their personal risk as well as the potential consequences of not taking action. Ways of effectively communicating these threats include outlining specific potential impacts to users, identifying those most at risk and providing explicit protective action to be taken. These concepts are applied to communicating anticipated QLCS events, particularly those events which may involve shorter-than-average lead time on tornado warnings.

Messaging the Impacts of a Nocturnal Tornado-Producing QLCS

Chris D. Bowman and Jared W. Leighton, NOAA/NWS Kansas City/Pleasant Hill, MO

The unique hazards presented by tornadic quasilinear convective systems, including the potential for strong tornadoes with minimal warning lead time, present challenges in communicating these risks to those who are most vulnerable. In many cases, such as with mobile home residents and large outdoor events, protective action must be taken hours in advance of these storms to ensure safety. However, conventional methods of communicating severe thunderstorm risk, may not elicit the desired public response if an area of concern is depicted in a lower risk area. This study presents a case in which several damaging nocturnal tornadoes occurred in an area that had been forecast with lower severe weather probabilities than nearby locations. While anticipated coverage of severe storms was expected to be lower for these locations than for areas further west, the transition to a nocturnal QLCS posed unique threats to certain portions of the population including mobile home residents. Alternative methods of communicating these threats are explored, including singling out those who were most vulnerable to the specific threats that night and providing explicit actions that could have been taken.

Partners Operational Weather Simulation (POWS) Program at NWS Louisville

Ryan J. Sharp and Theodore W. Funk, NOAA/NWS Louisville, KY

NWS Louisville (LMK) has developed a collaborative program where NWS partners participate in severe convective storm and winter storm training via the Weather Event Simulator (WES). The program, based on an idea from NWS St. Louis, initially is targeting broadcast TV meteorologists in and close to LMK’s CWA, but also will include others such as private meteorologists, university faculty, Corp of Engineers, and perhaps emergency managers. Benefits of the Partners Operational Weather Simulation (POWS) program include 1) provides training in severe and winter storm structure and the warning decision process, 2) allows partners to experience firsthand the complexity and strategies faced by NWS radar analysts, and 3) enhances relationships via one-to-one interaction.

The first case used is a severe quasi-linear convective system (QLCS) that raced across southern Indiana and north-central Kentucky on January 17, 2012. The QLCS produced several instances of wind damage and 6 tornadoes, including two rated EF-1 in the Louisville metro area. Participants are given an environmental briefing packet a day prior to arriving at our office. Once the simulation begins, partners learn knobology of the WES and how to use WarnGen. Thereafter, they analyze radar trends and issue warnings as needed, while thinking out loud so the facilitator can assess their understanding. A WESSL script provides storm reports and mesoscale forecast discussions during the event. The simulation lasts 75-90 minutes. At the end, the facilitator reviews the case, and determines warning POD, FAR, and lead times.

Participants have really enjoyed their experience. Here are two sample quotes. “I’ve already had a lot of respect for what you guys do, but this gives me a greater sense of appreciation. Other TV mets need to do this.” “This is great. It’s something I can use at work right away.”

This presentation will summarize the LMK POWS program so other NWS offices can initiate a similar program if desired. The presentation will concentrate on radar signatures/trends in the high shear, low CAPE January 17, 2012 QLCS including complex mesovortex evolution, which also offers excellent training for NWS meteorologists.

Dual Polarization and Quasi-Linear Convective System Education and Outreach to NWS Core Partners

Doug Cramer, NOAA/NWS Springfield, MO

Extensive research regarding line segment thunderstorms has been ongoing within WFO Springfield MO for several years. Within this research, a detailed radar analysis was conducted on numerous quasi-linear convective systems. A few radar signatures have been identified that typically are either associated with line segment tornadoes or lead up to line segment tornadoes. It is hypothesized that super-res reflectivity presentations make these features much more evident compared to lower resolution reflectivity data. In some cases, lower resolution data may not have indicated the presence of these features, while the super-res data shows these signatures in a clear manner. These signatures include front end nubs, coupled inflow notches, leading stratiform line segment structures containing meso-vorticies, and reflectivity tags. This presentation will show examples of how these signatures appear on radar reflectivity and velocity data.

Tornadic Debris Signatures Associated with Quasi-Linear Convective Systems

Rod Donavon, NOAA/NWS Des Moines, IA

Kevin Skow, NOAA/NWS Topeka, KS

Tornadoes associated with quasi-linear convective systems (QLCS) are rarely reported to National Weather Service warning meteorologists until post event. Often the first indication that a QLCS tornado is in progress is through the detection of a tornado debris signature (TDS); however, detection of these signatures vary based on land use. Land use across Iowa and surrounding areas are heavily dedicated to agricultural use. Debris from mature crops such as corn and soybeans from mid-July through October are highly conducive to lifting and can be lofted by weak tornadoes resulting in a TDS. Depressions in the correlation coefficient (CC) dual-polarization radar product located in favorable regions for QLCS tornadogenesis were investigated during this time frame. Ground and aerial surveys were conducted to detect evidence of tornadoes associated with these CC depressions. Many of these CC depressions did not meet criteria established by past research (Schultz et al., 2012; WDTD, 2014) as signatures occurred in areas of low reflectivity or regions of weak to non-existent storm-relative velocity.

Results from the Field(s): Aerial Depictions of Surface Vortex Damage Tracks Produced by Quasi-Linear Convective Systems

Kevin Skow, NOAA/NWS Topeka, KS

The proliferation of aerial and satellite-based datasets over the last decade has allowed for the augmentation of many National Weather Service tornado damage surveys, as well as the discovery of damage tracks that may not have been previously known to exist. However, this imagery is typically reserved for high-impact tornado events. Tornadoes produced via quasi-linear convective systems (QLCSs) rarely meet such criteria and are not typically studied to such degrees of detail. This work will review surface vortices from five QLCS events in central Iowa through a combination of on-demand imagery and photographic evidence collected via incidental surveys. These events include: 11 July 2011, 31 August 2014, 7 June 2015, 23 October 2015, and 11 November 2015. The predominantly flat, agricultural land cover of Iowa presents an excellent medium on which to document many scales of wind phenomena, especially mature corn fields. The wide variety of surface vortex damage tracks produced via QLCSs will be presented along with accompanying polarimetric WSR-88D radar signatures. Finally, an empirical probabilistic classification scale will be put forth in an attempt to isolate those QLCS surface vortex damage tracks that have the highest probability of reaching the definition of a tornado when surveyed via an aerial dataset.

An Analysis of Tornado Debris Signatures in the 30 June - 1 July 2014 Quasi-Linear Convective System Tornado Outbreak

Adam W. Clayton, Anthony W. Lyza, and Kevin Knupp, Severe Weather Institute - Radar and Lightning

Laboratories, University of Alabama in Huntsville (UAH-SWIRLL)

On 30 June - 1 July 2014, a tornadic quasi-linear convective system (QLCS) moved through northern Illinois and northern Indiana producing 29 confirmed tornadoes and numerous areas of significant straight-line wind damage. Damage surveys, along with Weather Surveillance Radar - 1988 Doppler (WSR-88D) and terminal Doppler weather radar (TDWR) data from northern Illinois and northern Indiana (KLOT, TMDW, and KIWX), were used to identify 39 mesovortices that formed during the lifespan of the QLCS. According to the damage surveys, eleven of the mesovortices were tornadic, producing EF0 to EF1 damage.

Since the NWS dual-polarization radar upgrade from 2011 to 2013, the identification of tornado debris signatures (TDSs) has become common practice in both operations and post-storm analysis. While the scientific literature is rich in papers on polarimetric TDS identification, the emphasis has largely been focused on supercell tornadoes producing EF-3 or greater damage (e.g., Ryzhkov et al. 2005; Kumjian and Ryzhkov 2008; Schultz et al. 2012 a,b). Previous studies utilized a cross-polar correlation coefficient (ρhv) threshold of < 0.8 to discriminate between hail and tornadic debris at S-band wavelength (< 0.7 at C-band). Some confirmed tornadoes from this case, as well as other areas of known damage that were not confirmed as tornadoes or not surveyed, featured ρhv values that met the < 0.8 criteria for S-band debris detection, but other signatures (including confirmed tornadoes) featured ρhv values in the 0.8 - 0.95 range. While melting hail is one additional common cause for lowered ρhv values aside from tornado debris, the wet-bulb zero height during this event was around 4.7 km AGL, as measured by aircraft soundings (AMDAR) from Chicago-Midway International Airport (KMDW). The lowered ρhv values were generally recorded under 1.75 km AGL, with most at or below 0.75 km AGL. Given the high wet-bulb zero height observed, it is unlikely that hail was present at the height of the lowered ρhv signatures observed during this event.

In this presentation, an analysis of TDSs associated with numerous mesovortices during this QLCS tornado outbreak will be offered. Observed TDS characteristics of interest include depth and diameter details for each observed TDS, merging of multiple TDSs into one broad signature, and additional tornadoes forming within debris fallout and subsequent tightening of associated ρhv signatures. Implications for real-time operational debris detection are discussed.

Some Thoughts on Radar-Observed Debris Signatures Associated with QLCS Mesovortices

Dan Miller, NOAA/NWS Duluth, MN

Paul Schlatter, NOAA/NWS Denver-Boulder, CO

Matthew Van Den Broeke, University of Nebraska-Lincoln, Lincoln, Nebraska

Since the upgrade to operational polarimetric capability on the WSR-88D radar network between 2010 and 2013, the ability to remotely sense debris lofted by tornadoes has become an extremely valuable input to the warning process for operational meteorologists. However, much of the focus for study of tornadic debris signatures (TDSs) has been on those associated with supercells.

This talk will focus on four QLCS mesovortices that were observed from the Duluth, MN WSR-88D radar (KDLH) during two MCS events, one on July 22, 2016, and the other on August 4, 2016. In both cases, signatures indicative of lofted debris were observed in polarimetric radar correlation coefficient and differential reflectivity data. However, damage surveys revealed that damage with all four of these mesovortices was not associated with tornadoes, but rather narrow and intense corridors of extreme non-tornadic wind damage; all located on the immediate southern or upshear flank of the parent mesovortex. All four mesovortices also occurred at very close range to KDLH, allowing for spatial and temporal sampling about as good as possible by a WSR-88D radar. A careful examination of the radar base moments and dual-pol variables actually the damage survey observations. This talk will examine, in detail, the evolution of these radar signatures presented with each of the four mesovortices in question, as well as some thoughts on the use of polarimetric radar data in QLCS mesovortex situations.

TDS Look-alike Signatures Along the Leading Edge of QLCSs and Implications for Warning Decision Making

Lewis Kanofsky, NOAA/NWS St. Louis, MO

NWS forecasters rely heavily on radar observations to assess the tornadic potential of thunderstorms. In some situations, dual-polarization radars can directly observe tornado-lofted debris. The characteristic radar appearance of lofted debris is known as the tornadic debris signature (TDS). At a bare minimum, a TDS is characterized by the co-located presence of three features: a vortex (inferred by radial velocity measurements), a good signal-to-noise ratio (based on sufficiently strong reflectivity values), and a localized decrease in correlation coefficient (CC). A co-located aberration in differential reflectivity (ZDR) may also be present. In an operational setting where a potentially tornadic circulation has already been identified, the sudden appearance of a localized CC minimum often serves as the first radar confirmation of a tornado and immediately prompts new warning and/or communication actions which convey the forecaster’s increased confidence that a tornado is present.

Most TDS studies to date have focused on supercell thunderstorms, therefore most of the TDS training currently available to NWS forecasters has also focused on supercell thunderstorms. Current training materials teach forecasters how to evaluate radar signatures to distinguish real TDSs from signatures which do not indicate tornadic debris, such as the low CC region associated with the inflow region of a supercell. TDSs associated with quasi-linear convective systems (QLCSs) have received comparatively little attention, and no equivalent guidance is currently available to forecasters regarding QLCS dual-pol radar signatures which might resemble TDSs but do not indicate tornadic debris.

Differences and Inconsistencies in the QLCS Tornado Warning Paradigm

Fred H. Glass, NOAA/NWS St. Louis, MO

Jacob Beitlich, NOAA/NWS Chanhassen, MN

Rod Donavon, NOAA/NWS Des Moines, IA

Ted Funk, NOAA/NWS Louisville, KY

Aaron Johnson, NOAA/NWS Dodge City, KS

Jason Schaumann, NOAA/NWS Springfield, MO

John Stoppkotte, NOAA/NWS North Platte, NE

In February 2016, the Tornado Warning Improvement Project (TWIP) Team was formed to address significant differences in the probability of detection and false alarm rates for tornado warnings within the National Weather Service’s Central Region (CR), resulting from inconsistent warning methodologies and knowledge. A major hurdle with knowledge is partially due to a limited infusion of recent advances in radar and tornado-based science into an impactful continual education program. The mission of the TWIP Team is to develop a consistent, scientific approach to the tornado warning process and a corresponding expert-level continuing education curriculum. Since the inception of the TWIP, team members have been actively engaged in examining the root causes of tornado warning inconsistencies between CR weather forecast offices. This examination includes a review of select tornadic events since 2014, results and comments from a detailed forecaster and management survey, and discussion with NWS colleagues examining similar issues in other NWS regions. Our findings indicate that perhaps the most challenging issue (and in need of immediate attention) is differences and inconsistencies in the QLCS tornado warning paradigm. There are a myriad of contributing factors to this problem including, but not limited to:

1) Wide-ranging knowledge of QLCS conceptual models, mesovortex dynamics, and favorable environmental conditions
2) Improper application of near storm environment data and threat assessment in the Warning Decision Making (WDM) process
3) Incomplete understanding of radar limitations
4) Incomplete understanding of the advantages and limitations of Conditional Tornado Probability Guidance
5) Complexities and challenges in the QLCS tornado WDM process
6) Subjective interpretation and evaluation of radar data, including varied individual warning thresholds
7) Real-time TDS identification, interpretation, and threat acceptance
8) Philosophical differences including misconceptions that all QLCS tornadoes are weak, short-lived and thus are not worthy of tornado warnings
9) Actual, functional experience with the QLCS tornado WDM process
10) Inconsistent damage survey policies and inconsistencies in damage identification

A handful of QLCS events from 2015-16 will be shown to illustrate some of these issues, and show opportunities where education and improvements to the tornado WDM process might produce more favorable results. This presentation will also serve as stimulus for the workshop panel discussion on QLCS tornadoes.

Friday, 10 March

Observations of Low-CAPE High-Shear QLCS Tornadic Events in the Lower Ohio Valley from 2005 to 2013

Patrick J. Spoden, Daniel R. Spaeth, Christine Wielgos, Mike York, Gregory Meffert,

Ryan J. Presley, Ken Ludington, and Robin Smith, NOAA/NWS Paducah, KY

QLCS (Quasi Linear Convective Systems) tornadoes are an operational challenge for most warning forecasters. The tornadoes are typically weak (< EF2) and short-lived. This study examines 46 QLCS tornadoes that occurred over 14 different events in the National Weather Service Paducah Kentucky warning area between 2005 and 2013. All of the tornadoes examined occurred in low CAPE (most unstable parcel CAPE (MUCAPE) < 1200 J kg-1) high shear (0 – 1 km shear vector magnitude > 18 m s-1) (LCHS) environments. These types of environments are even more challenging for forecasters as storms can move at over 30 ms-1 so rapid decision making skills are a must. Nearby environments were examined and analyzed by isolated or multiple tornadic events and an attempt was made to determine other potential deterministic parameters. The shear was generally located in the 0-1 km layer which made up 87% of the 0-3 km shear on average and more than half of the 0-6 km shear. The median 0-1 km shear value for all tornadoes and multiple tornadic events was 21 m s-1, with median values for isolated events at 23.9 m s-1. The median MUCAPE value was 627.8 J kg-1 for all tornadoes, with median values for isolated tornadoes at 377.1 J kg-1 while multiple tornadic events was 636.3 J kg-1. These storms occur in very moist environments with precipitable water value over 2.5 cm for all but one of the events. The locations of/and Vrot values were analyzed for up to 4 volume scans prior to or at tornadogenesis. The height of the maximum Vrot values were mostly above the lowest slice of available radar data suggesting a full storm analysis is needed. In an attempt to develop warning criteria recommendations, the median Vrot values for EF1 and EF2 tornadoes were analyzed. These values suggest a 12.9 to 17 m s-1 range is a possible starting point to consider issuing tornado warnings.

Comparison of Doppler Radar Correlation Coefficient, Spectrum Width, and Normalized Rotation in Areas of Rotational Circulations to Observed Convective Phenomena

Brian Greene, University of Oklahoma

Theodore Funk and Zack Taylor, NOAA/NWS Louisville, KY

Kevin Deitsch, NOAA/NWS St. Louis, MO

National Weather Service (NWS) meteorologists evaluate Doppler radar reflectivity and velocity trends to make informed severe weather warning decisions to protect life and property. However, spectrum width (SW), normalized rotation (NROT), and correlation coefficient (CC) also can be very useful to assess rotational circulation evolution within supercells and quasi-linear convective systems (QLCSs). Studies show that low CC values co-located with strong low-level rotation in supercells suggest a tornado on the ground. However, mesovortices associated with QLCSs are often weaker, smaller, shallower, and faster moving than their supercellular counterparts. As a result, tornado debris signatures (TDS) may be harder to discern. Therefore, this study examined radar data from past tornadic events to determine whether or not a combination of CC, SW, and NROT can successfully predict or identify tornadoes on radar.

A large sample of Doppler radar data from supercell and QLCS tornadic events in the Ohio and Mississippi River Valleys from 2008—2014 was collected and examined. Maximum values of SW and NROT as well as their heights above ground and depth of signals were recorded for as many possible radar scans before, during, and after documented tornadic events. Minimum CC values and depth of signal also were determined during and after tornadoes. Findings suggest that large values of SW and NROT coincident with rotation are accurate indicators of tornadic circulations and may offer some insight into tornado strength. This presentation will concentrate on data trends associated with QLCSs, but will compare them to supercells for reference.

Quasi-Linear Convective System (QLCS) and Non-Supercell (Landspout) Tornadoes Across Eastern Kentucky

Jonathan C. Guseman, Barrett T. Goudeau, and Edward C. Ray, NOAA/NWS Jackson, KY

A review of eastern Kentucky’s tornado climatology indicates that a primary storm mode responsible for tornadoes is the quasi-linear convective system (QLCS). These tornadoes tend to develop rapidly and are often difficult, if not impossible, to detect via Doppler radar. Multiple reasons exist for this, including the small-scale and shallow nature of these circulations, as well as the tendency for the radar beam to overshoot associated mesovortices that develop. A second type of non-supercell tornado, referred to as a landspout, is also very difficult to sense remotely, given its often transient and shallow nature. Forecasters must therefore possess a strong conceptual model of the processes responsible for generating these tornadoes. Further complicating matters across eastern Kentucky is the complexity of the varying terrain. This presentation will include a thorough analysis of both QLCS and non-supercell tornadoes, along with case studies showing conditions conducive for their development. Local research on the storm environment most conducive for tornadogenesis will be presented, including 0-3 km line normal wind shear which is one of the three primary ingredients for QLCS tornadic development. Finally, considerations and best practices will be explored to aid forecasters in their ability to maximize warning lead time and reduce false alarm rates for non-supercell and QLCS tornadoes.

Analysis of Unwarned Tornado Events from 2014-2015 across the National Weather Service Central Region
Rod Donavon, NOAA/NWS Des Moines, IA
Fred H. Glass, NOAA/NWS St. Louis, MO
Jacob Beitlich, NOAA/NWS Chanhassen, MN
Aaron Johnson, NOAA/NWS Dodge City, KS
Kevin Deitsch, NOAA/NWS St. Louis, MO
Ray Wolf, NOAA/NWS Davenport, IA
Alexander Gibbs, NOAA/NWS Davenport, IA
Andrew R. Dean, NOAA/NWS/NCEP/SPC Norman, OK

The National Weather Service Central Region Tornado Warning Improvement Project (TWIP) Team examined unwarned tornado events from 2014-2015 to ascertain potential training needs for warning meteorologists. Events were filtered by convective mode with numerous unwarned tornadoes associated with quasi-linear convective systems (QLCS) documented. WSR-88D radar data was analyzed utilizing Gibson Ridge GR2Analyst software to diagnose mesocyclone and mesovortex characteristics using storm relative velocity and Normalized Rotation (NROT) data. Detection of tornadic debris signatures were also reviewed. Hourly mesoanalysis data developed by the Storm Prediction Center was used to evaluate the near storm environment. External factors that may impact the warning decision making process including convective watch status and prior tornadoes on event day were considered. Finally, numerous events had spatial or temporal errors in Storm Data that resulted in false positive identification of unwarned tornadoes. The Storm Data errors had a negative contribution to the Government Performance and Results Act Goals.

Operational Detection of Descending Rear Inflow Jets and Implications on Quasi-Linear Convective System Tornado Warnings

Jason S. Schaumann, NOAA/NWS Springfield, MO

Research has shown that descending mesoscale rear inflow jets (RIJs) within quasi-linear convective systems (QLCS) to be a prominent source of damaging straight-line winds. Modeling studies have also shown that RIJs can play a direct role in mesovortex genesis, some of which produce tornadoes. Atkins and Laurent (2009) showed that parcels within a descending RIJ can acquire streamwise vorticity before subsequently being tilted and then stretched by the updraft region of a QLCS. The stretching of these parcels then leads to a rapid increase in vertical vorticity and the development of a mesovortex. This presentation will initially show radar data from cases which seem to support the Atkins and Laurent research. Radar interrogation techniques will then be examined with an intent to aid warning decision makers in detecting descending RIJ signatures. These techniques will then be tied into recent research on the development of QLCS tornado warning guidance based on the Schaumann and Przybylinski three ingredients method.

Reflectivity Signatures Associated with Line Segment Tornadoes

Doug Cramer, NOAA/NWS Springfield, MO

Examination of Radar Features and Mesoscale Parameters Which May Lead to an Increased Likelihood for Mesovortex Tornadoes

Robert Frye and Jason S. Schaumann, NOAA/NWS Springfield, MO

In 2012, Schaumann and Przybylinski conducted a study which concluded that the colocation of the following three ingredients favored mesovortex genesis and strong intensification within Quasi-Linear Convective Systems (QLCSs): 1. A portion of the QLCS in which the system cold pool and ambient low-level shear are nearly balanced or slightly shear-dominant. 2. Where 0-3 km line-normal bulk shear magnitudes are equal to or greater than 30 kt (15 ms -1). 3. Where a rear-inflow jet or enhanced outflow causes a surge or bow in the line. A 2013 Hollings Scholar study was then conducted to show the statistical significance of this “three ingredients method” for anticipating mesovortex genesis and strong intensification. A total of 67 mesovortices were identified, with 21 of the mesovortices producing at least one tornado. Statistical verification of the three ingredients method revealed a probability of detection of 79% and a false alarm rate of 23% for mesovortex genesis and strong intensification. Using the three ingredients method as a baseline for anticipating mesovortex genesis, additional radar features and mesoscale parameters were then examined in an attempt to show that their presence may lead to increased likelihood for mesovortex tornadoes. Radar and mesoscale data was therefore reexamined for the 67 mesovortex cases logged in the Hollings study. This presentation will briefly examine the radar features and mesoscale parameters which were sought out and logged for the 67 mesovortex cases. A statistical summary will then be presented on these features and parameters including frequency of occurrence and a comparison between tornadic and non-tornadic mesovortices. Based on these findings, the presentation will be concluded by offering general guidance to warning decision makers for considering QLCS Tornado Warnings.

Use of WSR-88D Spectrum Width as a Diagnostic and Prognostic Tool in QLCS Tornado Warning Decision-Making Process

Ray Wolf and Alex Gibbs, NOAA/National Weather Service, Davenport, IA

Tornado warning decision-making continues to be one of the most challenging tasks faced by National Weather Service forecasters, evidenced by the relatively low probability of detection and high false alarm ratio for warnings. In the past few years, two new tools were made available that aid the tornado warning process. The advent of dual polarization data, specifically the tornado debris signature, is helping improve detection at least for tornadoes near the radar, but it provides no lead time (at least initially). The Multi-Radar Multi-Sensor time trends of azimuthal shear, known as rotation tracks, permit straightforward temporal analysis of the circulation strength of potentially tornadic mesocyclones or mesovorticies. But despite past efforts to demonstrate the utility of spectrum width as a tornado warning decision-making tool, it remains underutilized in this process (while these other tools are coming into common usage).

This study assesses the utility of spectrum width as both a diagnostic and prognostic tool using a database of QLCS tornadoes from eastern Iowa and northern Illinois between 2008 and 2015. Spectrum width values observed by the lowest two elevation angles of 0.5° and 0.9° prior to and during tornadogenesis are analyzed to determine a threshold value, lead time, and POD. Results are summarized and recommendations are made for how spectrum width data should be worked into the tornado warning decision-making process.

Dual Doppler Observations of a Tornadic Quasi-Linear Convective System on 04 January 2015

Dustin Conrad and Kevin Knupp, University of Alabama-Huntsville

On 04 January 2015, a tornadic quasi-linear convective system (QLCS) impacted northern Alabama where an EF-1 tornado impacted the town of Albertville, located atop the Sand Mountain plateau in northeast Alabama. The tornado formed along a sharp wind shift along the leading edge of the QLCS in a high shear-low CAPE (HSLC) environment. Another non-tornadic mesovortex formed further to the south of the tornado. Doppler and dual-polarimetric radar data were collected from the University of Alabama-Huntsville's Advanced Radar for Meteorological and Observational Research (ARMOR) and the National Weather Service weather surveillance radar 1988-Doppler (WSR-88D) at Hytop, Alabama (KHTX). These data were complimented by meteorological surface observations and data from a 915-MHz wind profiler located at the University of Alabama in Huntsville’s Severe Weather Institute - Radar and Lightning Laboratories (UAH-SWIRLL), and surface data from the Gadsden, Alabama Automated Weather Observing System (KGAD AWOS). It is suspected that the main formation mechanism for the observed mesovortices in this event is horizontal shear instability (HSI) due to the extremely low CAPE and high low-level shear in the environment. Rayleigh, Fjørtoft stability criteria, and horizontal Richardson Number will be utilized in assessing if HSI is present along the leading edge of the QLCS. A possible wave interaction will also be investigated as the cause of the tornadic circulation becoming more intense than the southern vortex. These vortices will also be categorized by size, strength, and depth.

Microphysical Analysis of a Quasi-linear Convective System — A PECAN Case Study

Angelica Marchi, Robert M. Rauber, Greg M. McFarquhar, and Brian F. Jewett, University of Illinois at

Urbana-Champaign, Urbana, IL

An analysis of a quasi-linear convective system (QCLS) observed during one mission of the Plains Elevated Convection at Night (PECAN) project will be discussed in this presentation. PECAN was completed during the summer of 2015; it focused on nocturnal mesoscale convective systems initiating over the Great Plains region of the United States. A P-3 aircraft gathered data on this mission over western South Dakota performing dual-doppler flight legs and spiral descents and ascents in the stratiform precipitation regions behind convective lines of the storm. The analysis examines the effects of evaporation and sublimation on nocturnal inversions during the mesoscale convective system evolution. Analyses will be presented relating the microphysical characteristics of the QCLS transition zone to the storm system evolution. This system was sampled on 20 June 2015 beginning at 1:00 UTC in central South Dakota and ending at 9:00 UTC in central Minnesota. Specific focus will be placed on data from a dual-doppler leg during the first peak in convective line intensity and several spirals during a second peak in storm intensity.

Microphysical Characteristics of Select MCSs Observed During the 2015 PECAN Experiment

Daniel M. Stechman, Greg M. McFarquhar, Robert M. Rauber, and Brian F. Jewett, University of Illinois at

Urbana-Champaign, Urbana, IL

Michael M. Bell, Colorado State University, Ft. Collins, CO

Robert A. Black, NOAA/HRD, Miami, FL

David P. Jorgensen, NOAA/NSSL, Norman, OK

Terry J. Schuur, Coop. Institute for Mesoscale Meteorological Studies, Norman, OK

Numerous elevated nocturnal mesoscale convective systems (MCSs) were sampled by airborne and ground-based in-situ and remote instrumentation during the Plains Elevated Convection at Night (PECAN) experiment, which took place on the Great Plains from 1 June to 15 July 2015. The sizes and shapes of cloud hydrometeors were measured with a Precipitation Imaging Probe (PIP) and a Cloud Imaging Probe (CIP) installed on the National Oceanic and Atmospheric Administration (NOAA) P-3 aircraft, whereas the large-scale structure, reflectivity and vertical velocity were measured by the NOAA Tail Doppler Radar (TDR), and numerous ground-based mobile and WSR-88D radars. A total of 40 spiral ascents/descents in the transition zone, stratiform region, and rear anvil of MCSs were conducted by the NOAA P-3 during PECAN. An analysis of this unique dataset is presented and describes both time and space variations in the vertical distribution of particle habits, median mass diameters, total particle concentrations, derived total mass contents, and relative humidity. These microphysical properties are discussed in the context of storm structure and evolution as determined using radar analyses from select PECAN MCSs. The implications of these results are discussed in the pursuit of understanding the role of microphysical cooling processes in the evolution and maintenance of nocturnal elevated MCSs.

The Role of "Pulse" Downdrafts in the Evolution and Maintenance of Elevated Nocturnal MCSs

Bethany N. Fay, Robert M. Rauber, Brian F. Jewett, and Greg M. McFarquhar, University of Illinois at

Urbana-Champaign, Urbana, IL

The genesis and longevity of elevated nocturnal mesoscale convective systems (MCSs) are not well understood or simulated in numerical models. Here, the Weather Research and Forecasting (WRF) model is used to investigate whether downdrafts within the MCS can impinge on the stable nocturnal boundary layer, creating gravity waves that couple with the convection, maintaining the MCS.

To understand the role of these downdrafts, a retrospective simulation of a nocturnal elevated MCS on 9-10 August 2014 was performed, with 200m innermost nested grid output saved each minute. The system developed in eastern Colorado as a cluster of daytime supercells and transitioned to an elevated MCS as it entered western Kansas and Nebraska around sunset. Over the course of its lifetime, the simulated MCS developed a strong rear inflow jet (RIJ), several bowing segments, and a well-defined cold pool.

Toward the rear of the convective line and into the transition zone, downdraft “pulses” were present in the lowest 3 km. Lasting approximately 5-15 minutes, these pulses, which appeared to be tied to increases in rainwater content and evaporation, resulted in warming near the surface and occasionally a “separation” of the RIJ from the convective line. The presentation will address the effects of these downdraft pulses on the evolution of the MCS, and discuss results of a sensitivity study in which evaporational cooling was discontinued prior to pulse formation.

Overview of the 2 August 2015 Northern Michigan Severe Weather Outbreak

John Boris, Matt Gillen, and Aaron Mayhew, NOAA/NWS Gaylord, MI

Multiple rounds of severe thunderstorms impacted northern Lower Michigan during a 10-hour long outbreak of severe weather on 2 August 2015, resulting in more than $81 million in both hail and wind damage. Significant wind damage occurred around the Grand Traverse Bay and Sleeping Bear Dunes National Lakeshore in northwest Lower Michigan during this outbreak, as well as hailstones greater than four inches in diameter which damaged more than 350 structures along with numerous vehicles. Convective mode during this outbreak consisted of bowing segments/QLCSs as well as supercells. This presentation will provide a brief overview of the supporting environment and how initial convection and subsequent outflow boundary development contributed to later QLCS development as the event unfolded. This will be followed by a more detailed look at the damaging QLCS that impacted the Grand Traverse Bay region, including the tornadic potential of this particular storm.

Applying the Three-Ingredients Method to the QLCS Warning Process: An Interactive Case Review

John P. Gagan, NOAA/NWS Milwaukee/Sullivan, WI

Jason Schaumann, NOAA/NWS Springfield, MO

This interactive presentation will apply the three ingredients method of mesovortex anticipation and intensification (Schaumann and Przybylinksi, 2012) to a quasi-linear convective system (QLCS). The audience will apply the three ingredients in a step by step fashion to focus on the portion(s) of a QLCS where mesovortex generation and intensification is preferred. These portion(s) of the QLCS will then be investigated further by focusing on key radar features associated with an increased risk for tornado genesis. Ultimately the audience will be put in the role of the radar meteorologist and tasked to decide whether or not to issue warnings and if so, what type of warning (Severe Thunderstorm vs. Tornado).