May 18, 2021

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SLIGHT RISK OF SEVERE THUNDERSTORMS DAY 3 SPC OUTLOOK…FORECAST SYNOPSIS…ISSUED APR. 21, 2021…8:00 P.M. EDT

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Disclaimer:  This site is not affiliated with the National Hurricane Center, Hurricane Hunters, Storm Prediction Center, or National Weather Service.  ALL forecasts herein are the result of my analysis, and I am solely responsible for the content.  As ALWAYS, follow the National Hurricane Center, National Weather Service, and your local Emergency Management officials for emergency decisions.  In addition, this is strictly a FORECAST OFFICE.  I CANNOT make decisions regarding travel plans, etc.  My purpose, is to provide you the information, based solely on information I analyze, and the accuracy of the information at hand of the time of analysis, so you may make informed decisions.
(T. F. “Storm” Walsh)

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Greetings 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.).

Once again, as credit to the SPC, I will be incorporating the SPC outlook text if needed.

This post is for the current SPC DAY 3 CONVECTIVE OUTLOOK.

The Storm Prediction Center (SPC) has issued a SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY…

…SPC SUMMARY…
Isolated to scattered severe thunderstorms should occur Friday into Friday night from parts of the southern Plains into the lower Mississippi Valley. Large to very large hail, damaging winds, and isolated tornadoes all appear possible.

SPC DAY 3 CONVECTIVE OUTLOOK


Probability of severe weather within 25 miles of a point.
Hatched Area: 10% or greater probability of significant severe weather within 25 miles of a point

From the SPC synopsis (to save time in posting):
An upper trough should eject eastward from the Four Corners region and Southwest across the southern/central Plains on Friday, eventually reaching the lower/mid MS Valley by the end of the period. An EML with associated steep mid-level lapse rates will likely be present over much of OK/TX. A low-level jet should continue to transport low-level moisture northward through the day across the southern Plains, with a warm front potentially reaching as far north as the OK/KS border vicinity. At the surface, a weak low over the TX Panhandle Friday morning is forecast to develop southeastward to the vicinity of southwestern OK/western north TX by Friday evening while gradually deepening. A dryline should extend southward from this low across portions of west/central TX. The surface low should continue developing eastward to the lower MS Valley late Friday into early Saturday morning, with a composite dryline/cold front sweeping eastward across central/east TX. Rich low-level moisture should advance northward ahead of the low/front across much of LA and southern MS late in the period.

Based on further information contained and analyzed in the SPC outlook, it appears a capping inversion will be present first thing in the morning on Friday.  As conditions evolve during the day, rich moisture will be drawn northward and increase in the low levels, along with mid level lapse rates becoming steep (7.5-8.0 C/km), the presence of strong, deep layer wind shear, moderate to strong CAPE, and strong lifted indices just to mention a few, will allow for the development of organized severe thunderstorms and supercells close to the dryline and within the warm sector.  The threat for LARGE HAIL, DAMAGING THUNDERSTORM WINDS, and ISOLATED TORNADOES appear to be on tap.

Based on my analysis this evening of F5 DATA Severe Weather software, using the NAM-WRF 18Z run (current), severe and tornado indices and parameters are forecast to increase and are forecast at the moment to start reaching their strongest points beginning around 1:00 p.m. CDT through 10:00 p.m. CDT.  I am going to post the strongest of the indices which appear to occur around 10:00 p.m. CDT.  Keep in mind, as the model updates during the next few days, and conditions modify, these values could change.  These values are for Friday, APR. 23, 2021:

SBCAPE: 1000-2000 j/kg
MLCAPE: 1000-1500 j/kg
EHI: 1-5
LI: -6 to -10
STP: 5-14
VGP: 0.6-0.9

The following 2 links will provide some explanation of what these indices mean:
https://www.weather.gov/lmk/indices
http://www.theweatherprediction.com/severe/indices/
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.

Based on my analysis of these indices and their concentration, the following F5 DATA maps are outlined and indicate where the highest probability for where the strongest of the severe weather should occur, along with the highest probability of tornadic activity.  Again, I do expect these outlines to change as the model updates all day tomorrow.  I do intend to update tomorrow evening, and will have the SPC Mesoscale Discussion, SPC Convective Watches, and Radar maps posted, as well as the NWS Warning and Hazards map.
F5 DATA NAM-WRF 1:00 P.M. CDT APR. 23, 2021

F5 DATA NAM-WRF 4:00 P.M. CDT APR. 23, 2021

F5 DATA NAM-WRF 7:00 P.M. CDT APR. 23, 2021

F5 DATA NAM-WRF 10:00 P.M. CDT APR. 23, 2021

I intend to post a forecast on the upcoming coastal storm that develops around late Saturday evening / Sunday morning.

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
MEMBER WEST CENTRAL FLORIDA AMS

 

palmharborforecastcenter

2021-04-22 00:03:55

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