April 17, 2021

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SEVERE WEATHER FORECAST SYNOPSIS…ISSUED DEC. 29, 2020…9:00 P.M. EST

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(T. F. “Storm” Walsh)

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Good evening to everyone!
Please be aware, even though I do not post every night, rest assured I am continuously monitoring various areas for any significant weather.  I will be taking Sundays off (family time), unless we have active systems that may be posing a threat (i.e. Tropical, Winter Weather, Coastal Storms, etc.).

The Storm Prediction Center has issued a SLIGHT risk of severe thunderstorms for DEC. 31, 2020 FROM FAR SOUTHEAST TEXAS INTO THE CENTRAL GULF COAST STATES…

…SPC SUMMARY…
Severe thunderstorms associated with a tornado threat and wind damage will be possible Thursday into Thursday night from far southeast Texas into the lower Mississippi Valley and across the central Gulf Coast States.
SPC DAY 3 CONVECTIVE OUTLOOK


A negatively tilted low is forecast to deepen and move eastward during the day on Thursday.  Although instability is forecast to be weak, strong shear due to the interaction of the difference in direction between surface winds, and the flow and strength of a mid level jet, will provide support for organized storms, as the mid level jet will increase lift in the atmosphere, with the risk area being under the influence of the right entrance region of the jet.  The threat of tornadoes will be most prevalent from late afternoon into the over night hours.

Please note:
EHI = Energy Helicity Index
STP = Significant Tornado Parameter
VGP = Vorticity Generation Parameter
SRH = Storm Relative Helicity

VGP explained:  VGP = Vorticity Generation Parameter. The VGP is meant to estimate the rate of tilting and stretching of horizontal vorticity by a thunderstorm updraft. Values greater than 0.2 suggest an increasing possibility of tornadic storms.

In analysis VGP values were 0.2 to 0.5

The following link will explain a good portion of severe weather indices:
https://www.weather.gov/lmk/indices

Based on this information, and my analysis of the 18Z run of the NAM – WRF mesoscale model parameters from F5 DATA Severe Weather software (EHI, STP, VGP, SRH, EFFECTIVE SHEAR, and STENSRUD TORNADO RISK PERCENTAGES), the following maps indciate where the best probability lies for tornado development.  All times are CST:
NAM – WRF TORNADO PROBABILITY 3:00 P.M.

NAM – WRF TORNADO PROBABILITY 6:00 P.M.

NAM – WRF TORNADO PROBABILITY 9:00 P.M. CST

NAM – WRF TORNADO PROBABILITY MIDNIGHT CST

The following GIF loops will allow you to see the progression of the mid level jet, and significant tornado parameter values.  I am going to try and update again on this tomorrow evening, adding the SPC watches and mesoscale discussion maps, link to the SPC for you to view the DAY 1 outlook for Thursday, NWS Hazard and Warning display, and Doppler radar map (ANIMATED AND LINKED).

STP GIF MAP

500 MB JETSTREAM

You may direct any questions by contacting me personally, ANYTIME, at: twalsh22000@yahoo.com

Have a blessed evening!

T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST

 



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