Studies of severe convective windstorms using microwave imagery

1. Studies of severe convective windstorms using microwave imagery Kenneth L. Pryor Advisor: Dr. Belay Demoz November17, 2020

2. Outlineee • Motivation • Background: theory and observations • Research objectives • Timeline

3. Motivation Severe Convective Windstorm Prediction Convective Windstorms Theory, observations, impacts • Since 2000, the National Transportation Safety Board (NTSB) has recorded 48 downburst-related aircraft accidents over CONUS with 42 fatalities. The majority of these accidents involved small, single, or double-engine personal or instructional aircraft (i.e., general aviation). Accident occurrence was primarily on or near airdromes during the takeoff, approach, or landing phases of flight, presenting an additional public safety hazard. • Severe mesoscale convective systems (MCS), especially severe convective windstorms, cause major disruptions to society. • Between 1987 – 2002, MCS loss in the USA: • More than $3 billion in the United States, • average loss per event of $96 million. In addition, • 153 deaths and 2605 injuries (1986-2003) compared to 71 deaths for F0/F1 tornadoes (Ashley 2003) • Forecasting severe storms is a key issue: Need to conduct more research in • convective windstorm forecasting, short-term forecasting and nowcasting of convective system genesis, and satellite data exploitation and analysis of convective windstorm evolution.

4. ResearchObjectives Severe Convective Storms Theory, observations, impacts 2012 Derecho Thermodynamic environment, parameter and pattern evaluation Post-TC Sandy Evaluate models, theoretical and forecasting, parameters/patterns Localized MCS Thermodynamic environment, parameter and pattern evaluation Improved understanding of convective wind formation, evolution, and impacts.

5. Severe Convective Storms Deep moist convection (DMC): Presence of large CAPE, strong instability Most intense convection is associated with organized DMC. Linear convective systems Mesoscale convective systems Supercell storms Development of a rear-inflow jet is an internal process that can enhance storm outflow and sustain convection development. (Weisman 1992) Upwind (rearward) and downwind (forward) surface outflow interactions can enhance rear inflow and low-level updraft intensity, respectively. Theory Convective Windstorms Theory, observations, impacts Downdraft initiation: a departure from hydrostatic equilibrium: a = F/m = (-1/ρ)(dp/dz) + g(Tve – Tvp)/Tve a = F/m = (-1/ρ)(dp/dz) + g(ρo – ρf)/ρo The resultant force of the downward falling airmass is downward (negative buoyancy). ? (–) (–) (–) (–) ? ? Courtesy of Rob Seigel and Susan C. van den Heever, Global Precipitation Measurement (GPM, available online at https://gpm.nasa.gov/GPM)

6. Theory Convective Windstorms Theory, observations, impacts Severe Convective Storm Definition: Radar Observation Operational: Classified as “severe” when it contains: hail one inch in diameter or greater, winds gusting in excess of 50 knots (57.5 mph), or a tornado. 3 important conditions for severe thunderstorm development: Moisture of sufficient depth (to mid-troposphere) sufficiently large temperature lapse rate (large CAPE). Sufficient lifting of a moist parcel. Downdraft severity is governed by phase change and “loading” of ice-phase precipitation: induced buoyancy forces that result in a surface pressure perturbation, subsequent outflow, and the outward “bowing” of a linear multicell storm. DAL Outflow boundary Johns and Doswell (1992), Wakimoto (2001)

7. Theory: Summary of the Convective Wind Process Convective Windstorms Theory, observations, impacts Scales of motion for the different processes ⇒

8. Theory: Multi scale organization Convective Windstorms Theory, observations, impacts Fujita and Wakimoto (1981)

9. Summary of Research Questions Convective Windstorms Theory, observations, impacts • Rear-inflow jet: a) What are the dynamic and thermodynamic forcing factors for the development of a rear-inflow jet b) How does the rear-inflow jet further enhance downdraftintensity and convective windstorm longevity? 2) Rear-flow and convection interaction: a) How does thunderstorm outflow interact with the rear-inflow jet b) How does the rear-inflow jet enhance cold pool strength? 3) How does thunderstorm outflow enhance updraft intensity and downwind propagation of the MCS? This research is focused into the application of conceptual models to the prediction of severe convective windstorms operationally. I use three case studies to seek to answer these research questions across scales from the local to meso-synoptic range. ? ? ?

10. Data: Theory to Operations Convective Windstorms Theory, observations, impacts • Available data to processes and display: • Vertical variations in moisture using satellite profile data to infer atmospheric instability (e.g. NUCAPS, ATOVS, IASI) • Vertical wind profiles to infer low-level downdraft characteristics(BL wind profilers, NEXRAD VAD) • Cloud top temperature measured by satellite-based passive microwave (MW) sensors to infer convective storm intensity and precipitation phase (MHS, SSMIS) • Systematically consider other variations to the convective environment, such as deeper shear profiles and multidirectional shear profiles, as well as variations to the vertical profile of moisture. • Observational studies indicate that moderate to strong environmental wind shear is associated with development and maintenance of severe convective windstorm activity (Johns and Doswell 1992). • a thorough investigation of the nature of hodographs(vertical wind profile) is needed and could lead to improved forecasting techniques.

11. Severe Convective Storms Theory, observations, impacts Case Study Selection: Multi-scale Convection 2012 Derecho Thermodynamic environment, parameter and pattern evaluation Post-TC Sandy Evaluate models, theoretical and forecasting, parameters/patterns Localized MCS Thermodynamic environment, parameter and pattern evaluation Improved understanding of convective wind formation, evolution, and impacts. Scale of Organization

12. Localized MCS: Event Summary Localized MCS A cluster of thunderstorms developed over western Texas (April 27, 2020) then merged to form an intense squall line that tracked rapidly southeastward toward the Gulf Coastal Plain. As the storm passed over Del Rio, a severe downburst was generated that resulted in a wind gust of 67 knots, recorded at Del Rio International Airport at 0135 UTC April 28. Data available and preliminary work: During the afternoon of April 27, a NOAA-20 NOAA Unique Combined Atmospheric Processing System (NUCAPS); nearly six hours prior to a severe windstorm event. Next Generation Radar (NEXRAD) reflectivity imagery, satellite-based microwave sensor data and derived imagery effectively captured signatures indicative of a large storm ice precipitation content and lateral entrainment of sub-saturated air that fostered the generation of intense downdrafts. GOES-16 ABI Split Window IR imagery displayed general convective organization and intensity over a regional scale. Tornado-like damage to the Whispering Palms Inn. Courtesy of the Del Rio News-Herald

13. The Del Rio, Texas Severe Windstorm of 27 April 2020 Localized MCS A case study of this event was published in the 1 May 2020 NOAA STAR JPSS (JSTAR) Weekly Report and presented to the NUCAPS team on 6 May 2020. F-17 Orbit Pass 27 April 2020 DMSP F-17 overpass was optimal for retrieving cloud microphysical properties prior to downburst occurrence in the Del Rio area.

14. Thermodynamic analysis: NUCAPS Localized MCS EL Dewpoint LFC LR700-950 = 7.1 C/km LR700-950 = 7.1 C/km Temperature

15. Localized MCS TB = Tu+ τ∙[ε∙Ts+ (1-ε)∙Td] Ferraro et al. (1998) • The 91 GHz channel is an atmospheric window in the microwave spectrum. • Scattering by ice-phase precipitation particles, especially graupel, hail, and snow above the freezing level, causes 91 GHz brightness temperatures (TB) to be low- known as a “TB depression”(Ferraro et al. (2015), Laviola et al. (2020)). • Thus, convective rain bands tend to have very low TB, often lower than 200 K. • TBnear the storm centroid was remarkably low (~120 K) and corresponded to a maximum in graupel water path (GWP) values (> 10 mm), indicating the presence of a dense core of graupel/hail. Ice precip core Dry-air notches

16. Localized MCS • Differential brightness temperature difference (BTDR) between the horizontal and vertical polarization channels: • BTDR = 100*(log10(TB91H/TB91V)) • ZDR = 10*(log10(ZH/ZV)) • Small positive values of SSMIS-derived BTDR correspond to large graupel water path values (> 10 mm), and thus, to a mixture of rain, hail, and graupel. • Although Split Window IR imagery displayed general convective organization and intensity over a regional scale, GOES-16 was not able to resolve storm scale structure favorable for downbursts: i.e. ice precipitation cores, dry-air notches Ice precip core

17. Localized MCS Transition from a linear, multicell storm to a bow echo After downburst occurrence at Del Rio

18. New Science Value Added Localized MCS Exploitation of microwave window channel TB data to infer storm-structural characteristics: F-17 SSMIS 91 GHz window imagery, with overlying graupel water path measurements: indicate a concentrated area of remarkably cold cloud tops (TB < 120K) at the storm centroid presence of a large ice phase precipitation content Inward-directed V-shaped TB gradients on the downwind (eastern) flank of the storm: suggests the occurrence of wake entrainment of sub-saturated air subsequent downdraft acceleration by the process detailed in Knupp (1989). Absence of an apparent rear-inflow jet was likely a factor in the episodic and short-lived occurrence of downburst winds at Del Rio. Results to be published in a future Bulletin of the American Meteorological Society (BAMS) article titled “Utility of Satellite Retrievals of Atmospheric Profiles in Detecting and Monitoring Severe Weather Events at NOAA”. Expected publication date: Winter 2021

19. Severe Convective Storms Theory, observations, impacts 2012 Derecho Thermodynamic environment, parameter and pattern evaluation Post-TC Sandy Evaluate models, theoretical and forecasting, parameters/patterns Localized MCS Thermodynamic environment, parameter and pattern evaluation Improved understanding of convective wind formation, evolution, and impacts. Scale of Organization

20. Derecho Criteria and Definition June 2012 Derecho “ 1) There must be a concentrated area of reports consisting of convectively induced wind damage and/ or convective gusts > 25.7 m s−1 (50 kt). This area must have a major axis of at least 400 km (250 mi).” “2) The reports within this area must also exhibit a nonrandom pattern of occurrence; that is, the reports must show a pattern of chronological progression, whether as a singular swath (progressive) or a series of swaths (serial).” “3-4) Within the area there must be at least three reports, separated by 64 km (40 mi) or more, of either F1 or greater damage (Fujita 1971) and/or “significant” convective gusts of 33.4 m s−1 (65 kt) or greater. No more than three hours can elapse between wind damage events (gusts).” Johns and Hirt (1987), Corfidi et al. (2016)

21. The June 2012 Derecho June 2012 Derecho Classic progressive derecho Affected millions of people, 22 deaths Broke many records for highest winds Left five million without power Traveled 700 miles in 12 hours Courtesy of Corfidi et al. (2018): available online https://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm

22. The June 2012 Derecho NOAA-19 Orbit Passes 29 June 2012

23. Derecho Forecast Evaluation MCD #1314 2351 UTC 29 June: “...EXPECT STORMS TO CONTINUE TO ROLL BEYOND THE E SLOPES OF THE APPALACHIANS AND ACROSS MUCH OF VA OVER THE NEXT SEVERAL HOURS. ALONG WITH LIKELIHOOD FOR HAIL...DAMAGING WINDS WILL CONTINUE TO ACCOMPANY THIS MCS FOR AT LEAST THE NEXT COUPLE OF HOURS”. NWS/Storm Prediction Center (SPC) adequately indicated the likelihood of scattered severe winds over the Washington, DC – Baltimore, MD corridor as the derecho tracked east of the Appalachian Mountains during the late evening: However, the density and magnitude of severe wind events, and associated impacts, over the Washington, DC metropolitan area, including the adjacent MD and VA suburbs, was not anticipated by neither SPC nor NWSO Baltimore-Washington. New Science Value Added: The application of afternoon NUCAPS sounding profiles and derived parameters will provide more insight to the evolution of the convective lower troposphere. MW window channel data will more effectively interrogate evolving DCSs and reveal greater detail of storm structure, especially pertaining to convective wind generation. Correlate MW signatures and severe convective wind occurrence.

24. Thermodynamic Evaluation June 2012 Derecho Wet Microburst/Type B Inverted-V/Type A 12 km N of IAD MWPI: 3.2 WGP: 42 kt MWPI: 6.2 WGP: 55 kt Mid-tropospheric unsaturated layer LR670-950 = 7.6 C/km LR670-970 = 7 C/km

25. Metop-A MHS BT June 2012 Derecho a) b) Warm advection wing Dry-air notch RIJ Type 2 derecho echo pattern with a warm advection wing (Przybylinski 1995) that extended downwind (eastward) from the northern end of the bulging line echo. Microbursts occurred in Frederick County, MD, within the “warm advection wing” (Smith 1990) of the derecho.

26. Summary: Derecho case June 2012 Derecho Typical warm-season progressive derecho: associated with a major heat wave and an elevated mixed layer (EML)(Banacos and Ekster 2010, Corfidi et al. 2014). Metop-A MHS, with overlying Sterling, VA (LWX) NEXRAD reflectivity: Presence of the warm advection wing. A dry air notch, displayed as an inward (eastward) pointing TB gradient: Presence of a rear-inflow jet Sustained the MCS and the generation of downburst clusters in the DC-Baltimore corridor. Seminar/conference presentations featuring results of this study: Pryor, K. L., 2013: A Downburst Study of the 29-30 June 2012 North American Derecho, STAR Seminar, 30 April 2013. Pryor, K. L., 2014: Toward the Long-range Prediction of Severe Convective Windstorms, 2014 NOAA Satellite Science Week Meeting, 12 March 2014.

27. Severe Convective Storms Theory, observations, impacts 2012 Derecho Thermodynamic environment, parameter and pattern evaluation TC Laura Evaluate models, theoretical and forecasting, parameters/patterns Localized MCS Thermodynamic environment, parameter and pattern evaluation Improved understanding of convective wind formation, evolution, and impacts.

28. TC Laura Landfall – Louisiana Coast • Hurricane Laura made landfall at • Cameron, Louisiana near 0600 UTC 27 • August 2020. • Wind gust of 115 knots recorded at Lake • Charles Regional Airport, 50 km inland • from the point of landfall. GPM GMI 0300 UTC 27 August 2020 Courtesy U.S. Navy Courtesy NASA: https://go.nasa.gov/2IuPBwz

29. JPSS/S-NPP Microwave Imagery a) b) Dry air S-NPP ATMS 88 GHz brightness temperature image at 0751 UTC 27 August 2020 over the Hurricane Laura domain and an eastern Texas - southwestern Louisiana domain image with Shreveport (SHV) NEXRAD reflectivity overlying brightness temperature. Right-pointing triangle marks the location of Calcasieu Pass, Louisiana, left-pointing triangle marks the location of Lake Charles.

30. JPSS/S-NPP Microwave Sounding Comparison East of Eyewall Inner Eyewall a) b) MWPI: 1.65 WGP: 36.9 kt MWPI: 2.1 WGP: 38 kt LR750-950 = 5.0C/km Lower-tropospheric unsaturated layer

31. Summary: TC Laura Landfall During the morning of August 27, 2020, category 4 Hurricane Laura made landfall at Cameron, Louisiana, where a wind gust of 110 knots was recorded at Calcasieu Pass National Ocean Service (NOS) station. Wind gust of 115 knots recorded at Lake Charles Regional Airport, 50 km inland from the point of landfall. S-NPP ATMS 88 GHz window channel brightness temperature imagery showed the close proximity of peak measured winds in Lake Charles to the inner eyewall as well as the co-location of the coldest cloud top temperatures and highest radar reflectivity in the eyewall. These observations suggest that the highest eyewall winds likely correlated with a high concentration of convective ice-phase precipitation that could also serve as a forcing mechanism for intense downdrafts. In addition, ATMS imagery clearly displayed eye structure with a prominent reservoir of mid-tropospheric unsaturated air that could be entrained into the inner eyewall convection, resulting in downdraft enhancement and increased surface outflow intensity. This study of the mesoscale convective nature of the hurricane eyewall has strong implications for extreme wind warnings associated with the passage of the eyewall.

32. Severe Convective Storms Theory, observations, impacts 2012 Derecho Thermodynamic environment, parameter and pattern evaluation Post-TC Sandy Evaluate models, theoretical and forecasting, parameters/patterns Localized MCS Thermodynamic environment, parameter and pattern evaluation Improved understanding of convective wind formation, evolution, and impacts.

33. Conclusions TC Modeling Differences between the intensity and longevity of severe wind-producing convective storm systems are readily apparent in the comparison between April 2020 Del Rio, TX windstorm and the June 2012 North American Derecho. For the June 2012 derecho, rear inflow into the trailing stratiform precipitation region was readily detectable by Doppler radar and was instrumental in the generation severe outflow winds, especially during the second peak in DCS intensity that occurred east of the Appalachian Mountain region. RIJs also provide significant amounts of horizontal momentum that can be transported to the surface in heavy convective rainfall cells that can enhance outflow and resulting downburst winds. In Hurricane Laura, the highest eyewall winds likely correlated with a high concentration of convective ice-phase precipitation that could also serve as a forcing mechanism for intense downdrafts. ATMS imagery clearly displayed the intrusion of mid-tropospheric unsaturated air that could be entrained into the inner eyewall convection, resulting in downdraft enhancement and increased surface outflow intensity (Braun et al. 2010). This study of the mesoscale convective nature of the hurricane eyewall has strong implications for extreme wind warnings associated with the passage of the eyewall. Operational methods of employing high-resolution passive MW data and radar-derived velocity data will be developed to quantify the effect of RIJ development on convective wind intensity.