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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.
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF NORTH-CENTRAL AND NORTHEAST OK…SOUTHEAST KS…AND SOUTHWEST MO…
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF OK…KS…AR…MO…
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE CENTRAL GULF STATES…
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER NORTH-CENTRAL FL…
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE SOUTHERN TX PANHANDLE…
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF PA/NJ/NY…
Scattered strong to severe thunderstorms will be possible across parts of the south-central Plains into the Ozarks this afternoon and early evening, and across parts of the central Gulf Coast states late tonight into early Wednesday morning. Isolated strong storms will also be possible today across part of north Florida and in the vicinity of eastern Pennsylvania.
SPC CATEGORY SUMMARY
Analysis of the outlook this morning reveals scattered areas where a severe threat may be experienced. Based on the analysis of the SPC outlook maps, text, and forecast sounding data from the 12Z NAM-WRF run, the outlined areas in the SPC maps from the 1630Z update are of most concern. The NAM-WRF solution indicates the greatest threat for severe weather to be around 3:00 p.m.- 4:00 p.m. CDT over the south-central U.S.(OK, AR, MO) through 7:00 p.m. CDT, with s slim probability of an isolated area over AR later in the evening. The following outlines indicate where the best tornado probability may lie, based on forecast sounding data:
F5 DATA NAM-WRF 4:00 P.M. CDT
F5 DATA NAM-WRF 7:00 P.M. CDT
F5 DATA NAM-WRF 10:00 P.M. CDT
There is also noted a 2% and 5% tornado probability over portions of MS / AL. IF the NAM-WRF solution is accurate with the forecast sounding indices, this round of severe weather may occur very early on Wed. morning, within the time frame of after 3:00 a.m. CDT into 7:00 a.m. CDT. Based on the indices analyzed, the NAM-WRF projection for 4:00 a.m. CDT indicates the following outline for the best probability of experiencing tornadic activity:
F5 DATA NAM-WRF 4:00 A.M. CDT (4/5/2017)
This pretty much brings it close to the current Day 2 Outlook. Based on the forecast sounding data for the above map, indices begin to increase. Within the 5% tornado outline from SPC, I cannot rule out, possibly and isolated strong, and/or long track tornado.
For the Day 2 Outlook, based on my analysis, it could get fairly nasty. The SPC has designated a MODERATE risk of Severe Thunderstorms. The following risk areas are contained within the outlook:
…THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF AL/GA/SC AND THE FL PANHANDLE…
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE OH/TN VALLEYS TO THE SOUTHEAST…
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE OH VALLEY TO THE SOUTHEAST AND MID-ATLANTIC…
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK…
An outbreak of severe thunderstorms is likely Wednesday across much of the Southeast, continuing northward along and west of the Appalachians into the Tennessee and Ohio Valleys. This will include supercell development with a risk for tornadoes, some of which will be strong and long-lived, particularly across the Southeast. Large to very large hail and damaging straight-line winds also appear likely.
Based on my analysis of the current forecast sounding data from the NAM-WRF model, if the data is currently accurate (model is indicating some fairly high indices regarding EHI/STP, and CAPE values…which in my experience, the model has a tendency to be a little extreme in values the day before the event), I would not be surprised if SPC upgrades a small portion of the 45% / hatched area to a HIGH risk tomorrow. Based on forecast sounding indices, if they do not change, this event may have the probability of becoming a PDS (Particularly Dangerous Situation) within the SIGNIFICANT hatched area, especially within the 45% probability area. Modeling suggests the greatest indices to lie over a portion of MS, and more into AL, with the following values noted:
SBCAPE: 2000 – 3000 j/kg
MLCAPE 1000 – 2000 j/kg
Lifted Index: -6 to -8
Mid Level Lapse Rate: 7 – 7.5 C/km
EHI: 1 – 4
STP: 2 – 12
SWEAT INDEX: 400-450
The following link will explain somewhat, the meaning of the above values:
It is noted in the outlook, that convective activity may be ongoing as of 7:00 a.m. CDT over the risk areas, mainly in the south. However, based on the supplied data, things should begin to ramp up around 10:00 a.m. CDT over a portion of MS and over AL,mainly the southern third of the state. The model currently suggests that the event picks up better near 1:00 p.m. to 4:00 p.m. CDT, when the above indices would be experienced. Based on the above indices, there may be some strong, long tracked tornadoes experienced within that area of 45% with the significant hatching.
I have a pressing engagement tomorrow, but will try to post an update as soon as possible tomorrow afternoon.
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