A Tornadic Mini-Supercell With No Cloud-To-Ground Lightning
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A Tornadic Mini-Supercell With No
Cloud-To-Ground Lightning
Patrick D. MooreNational Weather Service Greer SC
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Post-Mortem Analysis
• At NWS Greer, post-mortems are done for significant weather events– Any tornado– Any weather related
fatality
• The goal is to increase our knowledge and identify systematic error, not to place blame
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19 April 2008 Tornado Event
• At 8:05 pm EDT (0005 UTC 20 Apr) a tornado touched down near the Double Shoals community in Cleveland County, NC
• No warning was issued• Why? National Geographic Television
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Synoptic Features 1200 UTC~12 hours to Impact
• 500 mb height, temperature, and wind barbs at 1200 UTC 19 April 2008
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Synoptic Features 1800 UTC~6 hours to Impact
• Surface observations, fronts, and pressure at 1800 UTC 19 April 2008
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Convective Environment 1900 UTC
~5 hours to Impact
• Supercells become more probable as effective bulk shear increases above 40 kt• 0-1 km Storm Relative Helicity greater than 100 m2s-2 suggests increased threat
of tornadoes with supercells• CAPE below 500 J kg-1 is a significant limitation to supercell development
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Convective Outlook 1934 UTC4 hours 29 minutes to Impact
ALTHOUGH INSTABILITY REMAINS VERY WEAK ACROSS THE REGION...SOME SFC HEATING HAS OCCURRED FROM CNTRL SC NWD INTO CNTRL VA. LOW-LEVEL LAPSE RATES SHOULD BE MAXIMIZED ALONG THIS CORRIDOR BY EARLY AFTERNOON AND A MARGINAL THREAT FOR WIND DAMAGE MAY DEVELOP.
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Convective Environment 2145 UTC
2 hours 20 minutes to Impact
• GOES-12 visible imagery at 2145 UTC 19 April 2008
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Convective Environment 2300 UTC
~1 hour to Impact
• Effective bulk shear increased from ~ 40 kt to > 50 kt• 0-1 km SRH increased from ~ 100 m2s-2 to ~ 150 m2s-2
• Most Unstable CAPE increased from < 500 J kg-1 to > 500 J kg-1
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2302 UTC - 2338 UTC 19 April63 – 27 minutes to Impact
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2340 UTC 19 April25 minutes to Impact
• Bogus funnel cloud report from Caldwell County, NC• Focused attention on rotation seen in new cell
moving into Cleveland County, NC• Cloud-to-ground lightning flash associated with old
nearby cell (first flash since 2252 UTC).
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2343 UTC 19 April22 minutes to Impact
• No cloud-to-ground lightning• No radar algorithm-identified meso or hail
alert
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2348 UTC 19 April17 minutes to Impact
• Storm has acquired supercell characteristics which are more apparent in smoothed data viewed with GR2Analyst
• No cloud-to-ground lightning• No radar algorithm defined meso or hail alerts
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2348 UTC 19 April17 minutes to Impact
• Supercell characteristics– Appendage/inflow notch– Weak Echo Region– Weak mesocyclone
• Freezing level ~ 9k ft
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2355 UTC 19 April10 minutes to Impact
• Skywarn report of rotation in cloud near Kingston (Cleveland County) NC
• Operator identified minimal mesocyclone– VR 21 kt, shear 0.012 s-1 at 43 km (KGSP 2353 UTC scan)– VR 19 kt, shear 0.008 s-1 at 33 km (TCLT 2354 UTC scan)
• No cloud-to-ground lightning since 2338 UTC• No radar algorithm identified meso or hail alerts
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2358 UTC 19 April7 minutes to Impact
Funnel Cloud near Lawndale NC,Report and image not relayed to NWS until next day
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0000 UTC 20 April5 minutes to Impact
KGSP
TCLT
KGSP
TCLT
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0003 UTC 20 April2 minutes to Impact
• Amateur cell phone video of wall cloud near Fallston, NC (Cleveland County). Report not relayed to NWS until next day
• TCLT storm relative motion contaminated with range folding, no 1.0 degree scan in this volume
• No cloud-to-ground lightning since 2338 UTC• No radar algorithm identified meso or hail alerts
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0007 UTC 20 April2 minutes after Impact
• Tornado on the ground southwest of Fallston, NC. Secondhand report relayed to NWS at 0015 UTC
• No cloud-to-ground lightning since 2338 UTC• No radar algorithm identified meso or hail alerts
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Radar Comparison 0007 UTC
• Operator identified mesocyclone remained in weak shear or minimal mesocyclone category before tornadogenesis
• KGSP radar algorithm did not identify mesocyclone, TCLT radar algorithm not available
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Radar Comparison 0007 UTC
• Rotational shear on both radars remained in minimal mesocyclone category prior to tornadogenesis
• Rotational shear on TCLT radar increased to tornado possible category on first volume scan after tornadogenesis
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Points of Failure on 19 April 2008
• Inadequate situation awareness of potential for supercells and tornadoes
• No prior experience with tornadoes generated by mini-supercells in the absence of cloud-to-ground lightning
• A mesocyclone too small to be properly sampled by radars?
• Range folded velocity data on TCLT radar, no 1.0 degree scan prior to tornado formation
• Critical storm reports not relayed to the NWS
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The Swiss Cheese Model
• Every step in a process is a defensive layer, but has the potential for failure
• In rare cases, a series of unrelated failures will occur, resulting in a catastrophic event
Duke University Medical Center
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What Went Right?
• Tornado Warning issued for western Lincoln County NC at 0015 UTC based on significant increase in rotational velocity on TCLT radar data
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What Went Right?
• Tornado touched down in Lincoln County NC at 0020 UTC, intermittent path through 0037 UTC
• Cloud-to-ground lightning began at 0040 UTC
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Questions?