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(T. F. “Storm” Walsh III)
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Good day everyone!
As of the 1300Z update from the Storm Prediction Center (SPC), a small ENHANCED risk are for Severe Thunderstorms has been designated ACROSS PORTIONS OF LA/MS/AL TO FL PANHANDLE…
A SLIGHT risk is in effect ACROSS THE GULF COAST STATES/LOWER MS RIVER VALLEY AND TN VALLEY…
A MARGINAL risk covers THE CENTRAL GULF COAST TO THE OHIO VALLEY AND MIDWEST…
Probability of one inch diameter hail or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of two inch diameter hail or larger within 25 miles of a point.
From the SPC:
Severe thunderstorms are expected today especially across the lower Mississippi Valley and central Gulf Coast states, but some strong to severe thunderstorms may occur as far north as the Tennessee Valley and Ohio Valley.
…Portions of LA/MS/AL to FL Panhandle… A southern-stream shortwave trough (and related mid/high-level speed max) will continue to amplify and spread generally east-southeastward today toward the central Gulf Coast States. Strengthening low/mid-level southwesterly winds will support the continued northeastward transport of low/middle 60s F surface dewpoints across additional portions of MS/AL.
Showers/thunderstorms are already increasing within the modestly moist early-day warm sector across southern/eastern LA into MS. Many of these storms should become increasingly surface based into late morning/early afternoon as additional moistening and destabilization occurs. 12Z observed soundings from Shreveport (SHV) and Lake Charles (LCH) sample severe-favorable thermodynamic profiles with very steep mid-level lapse near or excess of 8.0 C/km, aside from 35-45 kt of effective shear.
Steadily increasing deep-tropospheric winds and lengthening hodographs, in conjunction with cool mid-level temperatures (roughly -14C to -17C at 500 mb) and steepening lapse rates, appears likely to support supercells capable of large hail, along with some tornado/damaging wind risk, especially from mid/late morning into the afternoon. Storms may merge over time and grow upscale with at least a modestly increased damaging wind risk into AL and the FL Panhandle this afternoon, although the eastward progression of the presumed convective line may eventually outrun the greater low-level moistening/destabilization.
For additional details on the expected early-day evolution of storms, please reference Mesoscale Discussion 144.
…Tennessee Valley/Ohio Valley/Midwest…
Ahead of a cold front, moist advection will continue to occur in concert with 50+ knot low-level southwesterly winds. Mostly linear bands of strong to locally severe convection are ongoing early this morning from east-central AR into western TN. These storms should develop eastward across additional portions of TN and northern portions of MS/AL. While these storms are likely to develop east of the primary moist/instability axis, a modestly increasing potential for damaging winds, some hail and brief tornado risk can be expected during the day eastward into at least middle TN and northern portions of MS/AL.
Farther north into the Ohio Valley and Midwest, current thinking is that extensive ongoing precipitation south of the Ohio River and related cloud cover will tend to hinder appreciable destabilization. While weak buoyancy/strong vertical shear could support some stronger/potentially severe low-topped storms, the overall severe risk should remain limited.
Analysis of F5 DATA forecast soundings from the RAP model this morning, tends to suggest that the strongest severe weather, and tornado threat may hang back slightly further west. In fact, upon analysis of indexes and indices, of both the RAP and SPC SREF model, I am not sure as to why the slight risk was extended so far north, but I am sure there is good reason SPC has done this.
Based on forecast soundings of EHI, STP, SWEAT INDEX, and LIFTED INDICES, the RAP model 12Z run tends to suggest the following outlined areas may be where the best chance for supercell development to occur. The first outline covers from current, to 2:00 p.m. EST. The second outline from after 2:00 p.m. through 5:00 p.m. EST. These supercells, especially stronger cells displaying rotation, will have the capability of producing large damaging hail, damaging straight line thunderstorm winds, and tornadoes.
RAP SUPERCELL BEST PROBABILITY
The following outlined areas are suggested as to where the best probability of isolated tornadoes may occur. Based on various parameters, some isolated tornadoes could possibly be strong and long lived (long track), mainly over the areas of MS/AL, with the slight probability of some tornado activity lingering over the extreme west portion of LA.
The first outline covers from current, to 2:00 p.m. EST. The second outline from after 2:00 p.m. through 5:00 p.m. EST.
RAP BEST TORNADO PROBABILITY
At the time of issuing this synopsis, a TORNADO WATCH was in effect, and a TORNADO WARNING had already been issued earlier this morning for a portion of LA:
EARLIER TORNADO WARNING:
Residents within the ENHANCED and SLIGHT risk areas should monitor NOAA Weather Radio, local news outlets, and local NWS statements regarding today’s severe weather threat.
IF A TORNADO WARNING IS ISSUED FOR YOUR AREA…SEEK SHELTER IMMEDIATELY.
TORNADO SAFETY RULES WITH INSTRUCTION ON HOW TO TAKE COVER
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Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS