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Good day everyone!
The Storm Prediction Center (SPC) Norman, OK. has designated a SLIGHT risk of Severe Thunderstorms for PORTIONS OF SRN/ERN LA…MS…AL…FL PANHANDLE…SWRN GA…
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ELSEWHERE FROM SE TX TO SRN SC…
The greatest chance for Severe Weather WILL lie within the SLIGHT risk area, however based on the outlook text, I do expect the threat to shift eastward into the FL Panhandle, GA and the SC areas later this evening, with the continued threat of isolated tornadoes associated with a QLCS (Quasi Linear Convective System) type squall line.
Doppler radar this morning as of time of my analysis, indicated heavy thunderstorms already beginning to affect portions of the risk area. Based on my analysis of the outlook text, and forecast sounding parameters from the SPC SREF Computer model, F5 DATA Severe Weather software output running the RAP (or RUC [Rapid Update Cycle]) model, and upper air maps, a combination of high humidity and dewpoints into the 60 – 70F range, combined with increasing shear and SRH (Storm Relative Helicity) values in the 250 – 400 range, will provide enough thermodynamic and kinematic parameters for hail and isolated tornado activity throughout the day within the SLIGHT risk area. While the threat of tornadic activity is ongoing as of issuance of this synopsis, modeling indicates the greatest time frame for these threats should occur sometime after noon, EST, closer to late afternoon and early evening. I chose to utilize the RAP model output, even though it only extends out to 8:00 p.m. EST this evening, as it depicts the parameter coverage closest resembling the SPC outline. The following graphics indicate where the RAP places the greatest tornado risk between 5:00 p.m. and 8:00 p.m. EST
Helicity: A property of a moving fluid which represents the potential for helical flow (i.e. flow which follows the pattern of a corkscrew) to evolve. Helicity is proportional to the strength of the flow, the amount of vertical wind shear, and the amount of turning in the flow (i.e. vorticity). Atmospheric helicity is computed from the vertical wind profile in the lower part of the atmosphere (usually from the surface up to 3 km), and is measured relative to storm motion. Higher values of helicity (generally, around 150 m2/s2 or more) favor the development of mid-level rotation (i.e. mesocyclones). Extreme values can exceed 600 m2/s2.
At the time of analysis, the SPC had issued a Mesoscale discussion concerning the possibility of issuance of a TORNADO WATCH.
The following is a loop output from the RAP model, indicating the forecast STP (Significant Tornado Parameter). A STP of 1 or greater indicates a higher probability of tornadic activity. The higher on the scale, the greater the potential for significant tornado occurrence (EF2 – EF5). Given the forecast STP in both the graphic and in modeling, I am not looking for any strong tornadoes today.
Residents within the risk areas should monitor NOAA Weather Radio, and NWS Statements and Warnings. Statements and warnings can be accessed by clicking on the NWS Hazards display graphic over the area of concern. IF a TORNADO WARNING is issued for your area, SEEK SHELTER IMMEDIATELY!
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST / SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
OFFICIAL SKYWARN SPOTTER (ADVANCED)