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(T. F. “Storm” Walsh III)
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Good day everyone!
The Storm Prediction Center (SPC) has designated the following Severe Weather Risk areas in the Day 1 Convective Outlook, as of the 1630Z issuance:
…THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF CENTRAL AND SOUTHERN GEORGIA INTO CENTRAL SOUTH CAROLINA…
…THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS SURROUNDING THE HIGH FROM PORTIONS OF SOUTH CAROLINA TO GEORGIA AND ALABAMA AND THEN NORTHWARD INTO SOUTH-CENTRAL KENTUCKY…
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SURROUNDING THE MODERATE FROM PORTIONS OF THE OHIO VALLEY REGION TO THE SOUTHEAST STATES AND MID-ATLANTIC…
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED FROM PORTIONS OF THE LOWER GREAT LAKES REGION TO THE SOUTHEAST STATES AND MID-ATLANTIC…
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE EASTERN STATES…
An outbreak of severe thunderstorms is expected from portions of the Southeast States to the Ohio Valley region and eastward to the Mid-Atlantic. Significant tornadoes will be possible, especially from parts of central and southern Georgia into South Carolina, and also from parts of eastern Alabama into south-central Kentucky. In addition, very large hail, and damaging wind gusts are expected.
PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1151 AM CDT WED APR 05 2017
…Outbreak of tornadoes and severe thunderstorms expected over parts of the southeast US today into tonight… * LOCATIONS… Georgia South Carolina Eastern Alabama Middle Tennessee South-central Kentucky * HAZARDS… Numerous tornadoes, several intense and long track Widespread large hail, some baseball size Scattered damaging winds * SUMMARY… An outbreak of severe thunderstorms is expected from portions of the Southeast States to the Ohio Valley region and eastward to the Mid-Atlantic. Significant tornadoes will be possible, especially from parts of central and southern Georgia into South Carolina, and also from parts of eastern Alabama into south-central Kentucky. In addition, very large hail, and damaging wind gusts are expected. Preparedness actions… Review your severe weather safety procedures for the possibility of dangerous weather today. Stay tuned to NOAA Weather Radio, weather.gov, or other media for watches and warnings. A tornado watch means that conditions are favorable for tornadoes to form during the next several hours. If a tornado warning is issued for your area, move to a place of safety, ideally in a basement or interior room on the lowest floor of a sturdy building.
SPC CATEGORY SUMMARY
Based on the outlook text, severe weather is currently ongoing. It is indicated that SIGNIFICANT LARGE HAIL and SIGNIFICANT TORNADOES (up to EF5 ), ARE FORECAST TO BE ASSOCIATED WITHIN VERY STRONG SUPERCELLS. These tornadoes may very well be long track as well. These 2 events will be most common, or have the highest probability within the hatched areas noted in the SPC outlook maps.
Based on current forecast sounding data from F5 DATA software, I went with the current RAP model, as the NAM-WRF solution appears to be lagging behind where the current severe weather and tornadoes are occurring. The model solution suggests the best probability for the stronger tornado activity, to lie within the following outlined areas, however to reiterate, will most likely occur as well just outside these outlines, IAW the SPC Tornado Probability map.
F5 DATA RAP MODEL 1:00 P.M. CDT
F5 DATA RAP MODEL 4:00 P.M. CDT
F5 DATA RAP MODEL 7:00 P.M. CDT
F5 DATA RAP MODEL 9:00 P.M. CDT
At the time of this update a PDS (Particularly Dangerous Situation) TORNADO WATCH was placed into effect:
The following forecast sounding indices were noted in analysis, with the exception that SPC is forecasting MLCAPE of 2000 – 3000 j/kg:
SBCAPE: 1500 – 3000 j/kg
MLCAPE: 1000 – 2000 j/kg
LIFTED INDEX: -6 to -8
SHOWALTER INDEX: -2 to -4
EHI: 2 – 4
3KM VGP: 0.3 – 0.4
1 KM VGP: 0.2 – 0.8
STP: 3 – 12
1KM HELICITY: 100 – 200 m2 / s2
3KM HELICITY: 200 – 300 m2 / s2
The following explains these indices:
VGP – Vorticity Generation Potential. Another experimental field used to predict supercell tornadoes. Based on the work of Rasmussen and Wilhelmson (1982) it relates CAPE and shear. It is defined as the sqrt(CAPE) times the 0-3 km mean shear. The units are m/s2 (an acceleration) or m/s times 1/s which is the product of w times vorticity – a tilting term. It is possible to have high values of VGP when helicity (and the EHI) is low. The VGP climatology shows that supercell tornadoes rarely happen with VGP less than 0.3, and go from unlikely to likely as VGP goes from 0.5 to 0.6, and are likely above 0.6. It’s also possible that the larger the VGP the stronger the tornado. The VGP was developed by Erik Rasmussen for use over the central plains and may or may not be valid over other regions. Problems – Unknown. But, since it depends on the assumed CAPE and depth of the inflow wind layer, it might inherit their problems.
Based on analysis of upper level charts, the moderate risk areas will be under the influence of a strong jetstreak, with the northern portions of AL/GA close to, or slightly within the left exit region. Analysis of the current 500 mb chart indicates storms may become stronger this afternoon, as the 500 mb trof becomes more negatively tilted.
Based on forecast soundings, this a PDS (Particularly Dangerous Situation), and has the potential to become DEADLY!
IF A TORNADO WARNING IS ISSUED FOR YOUR AREA…SEEK SHELTER IMMEDIATELY!
The following graphics are linked to their respective sites. Mouse over and click on the graphics for up to date information.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS