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(T. F. “Storm” Walsh III)
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There is a MARGINAL risk FROM EXTREME NORTHEAST TX TO WESTERN IN…
Scattered severe thunderstorms are expected during the second half of the period from the Arkansas/Missouri vicinity into portions of the lower Ohio Valley area.
Analysis of the SPC outlook text indicates a fast moving shortwave trough is expected to eject across the southern Rockies, and into the KS/OK area by Monday evening (00Z or 7:00 p.m EST). This will setup a veering LLJ (Low Level Jet). SPC indicates strong capping to be in place through late afternoon, and by early evening, large scale forcing for ascent is forecast to enhance lapse rates, allowing for supercell development by mid evening. Should these thunderstorms become surface based, and surface based updrafts develop, this could allow for development of a few tornadoes.
Based on forecast sounding solutions from F5 DATA software, there is quite a discrepancy in the GFS and NAM-WRF solutions. I believe the forecast indices may be a little on the aggressive side with the NAM at the moment, and will re-evaluate soundings tomorrow, against the RAP model output, and SPC SREF solution. However, given the premise of a capping environment for most of the day, with the probability of it eroding, or “busting”, there IS always that probability the current forecast soundings may be close. For right now, with that in mind, the NAM-WRF suggests the strongest, and most probable severe weather threat, and isolated tornado threat, may occur over Arkansas. This may occur after late evening, and well into early morning hours. The following are the current forecast SWEAT values and STP values
SWEAT INDEX (SEVERE WEATHER THREAT):
<272 Thunderstorms unlikely
273-299 Non-severe thunderstorms are possible
300-400 Thunderstorms will approach severe limits
401-600 Increased risk of severe storms or isolated tornadoes
601-800 Tornadoes almost always occur
The significant tornado parameter (effective layer) is another composite index. Like the supercell composite, it contains several ingredients. The soup that makes up the significant tornado parameter includes effective bulk wind difference, effective storm-relative helicity, 100mb mean parcel CAPE (MLCAPE), and 100mb mean parcel height (MILCL). Values greater than 1 have been associated with a majority of tornadoes that have been rated significant/strong (which is a rating of EF2 or greater). Non-tornadic supercells, on the other hand, are often associated with significant tornado parameters of less than 1.
The SPC has indicate a SLIGHT risk of Severe Thunderstorms ACROSS THE MID MISSISSIPPI/OHIO/TENNESSEE VALLEYS AND VICINITY…
There is a MARGINAL risk SURROUNDING THE SLIGHT RISK AREA…
Showers and scattered thunderstorms are forecast to affect the mid Mississippi, Ohio, and Tennessee Valley areas, and later spreading eastward across the Appalachians. Isolated strong/locally severe storms will be possible mainly west of the mountains.
I am holding off on analysis of forecast soundings for day 3, until Tues. morning, given the discrepancies in current model solutions. I will try to have an update on this on Tues. as the day 1 outlook. From the day 3 text:
Mid MS/OH/TN Valleys and vicinity… A complex scenario remains evident for Day 3/Tuesday, with model differences still evident and corresponding low confidence with respect to forecast details of convective mode/intensity/evolution ahead of the advancing cold front.
Barring any unforeseen circumstances, I should have updates on both days.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS