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Cool Season Strong Tornadoes in the Southeast United States Jared L. Guyer NOAA/NWS Storm Prediction Center March 1, 2007.

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Presentation on theme: "Cool Season Strong Tornadoes in the Southeast United States Jared L. Guyer NOAA/NWS Storm Prediction Center March 1, 2007."— Presentation transcript:

1 Cool Season Strong Tornadoes in the Southeast United States Jared L. Guyer NOAA/NWS Storm Prediction Center March 1, 2007 – National Severe Weather Workshop

2 Early Morning Florida Tornadoes February 2, 2007 Images courtesy NWS Melbourne The Villages / Lady Lake Tornado EF-3 Tornado with a 16.5 mile track and 8 Fatalities 3:08 a.m. – 3:25 a.m. EST Lady Lake Church Mobile Homes Demolished in Lady Lake

3 Early Morning Florida Tornadoes February 2, 2007 Images courtesy NWS Melbourne Lake Mack / Deland Tornado EF-3 Tornado with 26 mile track and 13 Fatalities 3:37 a.m. – 4:10 a.m. EST Motor Home Destroyed at Lake Mack Mobile Home Frame at Lake Mack

4 Introduction An ongoing SPC study to help identify a set of patterns, parameters, and conditions that are commonly associated with the development of cool season tornadoes in the Southeast States, with a focus on strong (F2+ greater) tornadoes. An ongoing SPC study to help identify a set of patterns, parameters, and conditions that are commonly associated with the development of cool season tornadoes in the Southeast States, with a focus on strong (F2+ greater) tornadoes. Will also discuss some non-meteorological aspects of these tornado occurrences Will also discuss some non-meteorological aspects of these tornado occurrences

5 Study Introduction 68% of all December through February tornadoes in US occur in southeast (Galway and Pearson 1981) 68% of all December through February tornadoes in US occur in southeast (Galway and Pearson 1981) Cool-season conditions Cool-season conditions Favorable wind shear common, however… Favorable wind shear common, however… Instability usually questionable ingredient for supercell development Instability usually questionable ingredient for supercell development Uncertainty regarding low-level moisture and atmospheric instability can make forecasting such events quite challenging for operational forecasters (Vescio and Thompson 1993). Uncertainty regarding low-level moisture and atmospheric instability can make forecasting such events quite challenging for operational forecasters (Vescio and Thompson 1993).

6 Project Definitions Cool-SeasonCool-Season October 15 – February 15 October 15 – February 15 Examined 20 cool seasons Examined 20 cool seasons through through Strong tornado Strong tornado F2+ intensity F2+ intensity Focus on non-tropical systems Focus on non-tropical systems

7 Cool Season F2+ Tornadoes All F2-F5 Tornadoes between October 15 - February 15 from to F2+ Tornadoes (F2 76%, F3 20%, F4 4%, F5 0%) from 100 tornado days Long term yearly average: 12 F2+ tornadoes amongst 5 tornado days each year Tornado Tracks in Red

8 Research Methodology Past Upper Air Data Past Upper Air Data North America Regional Reanalysis (NARR) data at 6 hour intervals (00 UTC, 06 UTC, 12 UTC, 18 UTC) North America Regional Reanalysis (NARR) data at 6 hour intervals (00 UTC, 06 UTC, 12 UTC, 18 UTC) Mandatory level winds, geopotential heights, and temperatures Mandatory level winds, geopotential heights, and temperatures Precipitable water, surface temperature, surface dewpoint Precipitable water, surface temperature, surface dewpoint MSLP, 0-3 km helicity, lowest 180 mb most unstable CAPE (MUCAPE) MSLP, 0-3 km helicity, lowest 180 mb most unstable CAPE (MUCAPE) Proximity Upper Air Soundings Proximity Upper Air Soundings Constraints of 200 km and +- 3 hr Constraints of 200 km and +- 3 hr 57 soundings amongst 50 tornado days 57 soundings amongst 50 tornado days Modified for nearest surface inflow observation of temperature, dewpoint, and wind speed/direction with 0-1 hr preceding the tornado Modified for nearest surface inflow observation of temperature, dewpoint, and wind speed/direction with 0-1 hr preceding the tornado

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10 Research Findings – 500 mb Patterns 72% of cases associated with the anticyclonic south fringe of a 500 mb jet 20% of cases coincided with the 500 mb jet nose and/or beneath the jet axis Strength of the mid/upper level jet did not appear to discriminate between isolated strong tornado events vs. larger outbreaks Example 500 mb - 12 UTC 24 November F2+ Tornadoes

11 Example Upper Air Sounding Observed RAOB preceding (23z XMR) the February 2, 2007 Tornadoes Deep moisture 68 F Temp 66 F Dewpoint Extremely strong wind fields favorable for rotating storms Each Bar = 10 kt Each Flag = 50 kt Modest Convective Instability (CAPE) Height (km) Dewpoint Temperature

12 80% Southeast Cool Season F2+ Tornadoes Surface Dewpoints (°F) Precipitable Water (inches) 50% Mean Value Derived from upper air soundings in proximity to F2+ Tornado Events 90 th Percentile 10 th Percentile 25 th Percentile 75 th Percentile

13 Southeast Cool Season F2+ Tornadoes CAPE (J/kg) Derived from upper air soundings in proximity to F2+ Tornado Events

14 Southeast Cool Season F2+ Tornadoes 25 F2+ Tornadoes in November-February associated with < 500 J/kg MLCAPE in Storm environment data provided by Schneider and Dean, SPC

15 Southeast Cool Season F2+ Tornadoes Vertical Shear (kt) Storm Relative Helicity (m2/s2) Derived from upper air soundings in proximity to F2+ Tornado Events

16 Gulf Buoy Data Preceding Cool Season F2+ Tornadoes Evans and Guyer 2006 Surface Dewpoint with Tornado Time Preceding the Tornado Buoy Dewpoint Preceding Tornado Event Gulf of Mexico Buoy data (#42002) Preceding F2+ Tornadoes in the Cool Season

17 18 UTC BMX 16 Dec UTC BMX 16 Feb 2001 Meteorological Caveats Parameters Alone Dont Tell the Whole Story Tornadic supercell (F4 at TCL) Bow Echo/ Derecho Slide courtesy Steve Weiss, SPC

18 Meteorological Summary Similar to previous studies, confirmed the predominance of high shear/low instability regimes with cool season Southeast U.S. F2+ tornadoes Similar to previous studies, confirmed the predominance of high shear/low instability regimes with cool season Southeast U.S. F2+ tornadoes Pronounced speed shear component in the lowest few km Pronounced speed shear component in the lowest few km 850 mb wind speeds typically >40 kt 850 mb wind speeds typically >40 kt 0-1 km bulk shear >25 kt 0-1 km bulk shear >25 kt Only modest amounts of convective instability is typically needed Only modest amounts of convective instability is typically needed CAPE values may be J/kg or less CAPE values may be J/kg or less Given a favorable synoptic system (and associated wind fields), measures of low level moisture (dewpoints and/or mixing ratios) appear to be paramount for anticipating Southeast U.S. F2+ tornadoes during the cool season. Given a favorable synoptic system (and associated wind fields), measures of low level moisture (dewpoints and/or mixing ratios) appear to be paramount for anticipating Southeast U.S. F2+ tornadoes during the cool season.

19 Cool Season F2+ Tornadoes All F2-F5 Tornadoes between October 15 - February 15 from to Midnight

20 Overnight Cool Season Tornadoes Since November 2006, of tornado fatalities have occurred during the overnight hours Since November 2006, 88% of tornado fatalities have occurred during the overnight hours 30 nighttime fatalities (of 34 total) associated with 5 killer tornadoes 30 nighttime fatalities (of 34 total) associated with 5 killer tornadoes Lady Lake, FL and Paisley/DeLand, FL on February 2, 2007 (20 fatalities total) Lady Lake, FL and Paisley/DeLand, FL on February 2, 2007 (20 fatalities total) Gentilly, LA on February 13, 2007 (1 fatality) Gentilly, LA on February 13, 2007 (1 fatality) Riegelwood, NC on November 16, 2006 (8 fatalities) Riegelwood, NC on November 16, 2006 (8 fatalities) Montpelier, LA on November 15, 2006 (1 fatality) Montpelier, LA on November 15, 2006 (1 fatality) Since 1998, the biggest single killer tornado was November 6, 2005 in Evansville, IN at 2:00 am CST (25 fatalities) Since 1998, the biggest single killer tornado was November 6, 2005 in Evansville, IN at 2:00 am CST (25 fatalities)

21 Non-Meteorological Factors A tendency for events to occur during the late evening/overnight hours during the cool season in the southeast United States A tendency for events to occur during the late evening/overnight hours during the cool season in the southeast United States Getting the message out before most people go to sleep – late evening news? Getting the message out before most people go to sleep – late evening news? What late night precautions do people take? What late night precautions do people take? NOAA Weather Radio NOAA Weather Radio Even in more modest scenarios (i.e. not a larger outbreak), the potential may exist for strong tornadoes in a more isolated sense given the conditions (i.e. strong wind shear) Even in more modest scenarios (i.e. not a larger outbreak), the potential may exist for strong tornadoes in a more isolated sense given the conditions (i.e. strong wind shear) A low probability and/or coverage, but it may be a high end event A low probability and/or coverage, but it may be a high end event Scenario leads to an inherent tendency for occasional false alarm Scenario leads to an inherent tendency for occasional false alarm Expected severe coverage may not be particularly high, but conditional potential exists for a strong tornado Expected severe coverage may not be particularly high, but conditional potential exists for a strong tornado Public education of the caveats associated with such cool season/nocturnal scenarios Public education of the caveats associated with such cool season/nocturnal scenarios A large part of a tornado watch may not end up experiencing widespread severe weather, but there is conditional potential for strong tornadoes where supercells occur in the watch A large part of a tornado watch may not end up experiencing widespread severe weather, but there is conditional potential for strong tornadoes where supercells occur in the watch

22 Summary Future Research: Future Research: Focus on solely hail/wind, and possibly weak tornado, events to derive a separate proximity sounding dataset for comparative purposes. (Summer 2007) Focus on solely hail/wind, and possibly weak tornado, events to derive a separate proximity sounding dataset for comparative purposes. (Summer 2007) Closer examination of moisture return trends via buoy data and surface data. Closer examination of moisture return trends via buoy data and surface data. My coauthors on this study: My coauthors on this study: David A. Imy, NOAA/NWS Storm Prediction Center David A. Imy, NOAA/NWS Storm Prediction Center Amanda Kis, University of Wisconsin Amanda Kis, University of Wisconsin 2005 NOAA Hollings Scholarship program 2005 NOAA Hollings Scholarship program Karretta Venable, Jackson State University Karretta Venable, Jackson State University 2005 Research Experiences for Undergraduates (REU) 2005 Research Experiences for Undergraduates (REU)

23 Cool Season Strong Tornadoes in the Southeast United States Jared L. Guyer NOAA/NWS Storm Prediction Center March 1, 2007 – National Severe Weather Workshop


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