Mesoscale Discussion 0508 NWS Storm Prediction Center Norman OK 0848 PM CDT Sun Apr 20 2025 Areas affected...east Arkansas...west Tennessee...far west Kentucky Concerning...Tornado Watch 156... Valid 210148Z - 210315Z The severe weather threat for Tornado Watch 156 continues. SUMMARY...Thunderstorms continue to move east across Arkansas. A tornado threat will continue through the evening before beginning to lessen toward midnight. Trends will be monitored for potential watch across far west Tennessee and Kentucky DISCUSSION...A broken line of thunderstorms, many exhibiting at least transient supercellular characteristics, will continue to move east this evening. Recent VAD wind profiles from NQA (Memphis 88D) show the low-level jet (as proxied by the 0-1 km shear value) has increased from around 15-20 knots three hours ago to nearly 35 knots at present. Additionally, the VAD profile shows considerable clockwise turning below three kilometers, with much of that in the lowest one kilometer AGL (0-1 km SRH of nearly 350 m2/s2). Presently, SPC mesoanalysis shows a significant reduction in instability across eastern Arkansas as compared to areas to the west. However, given the upstream airmass remains moist and the strength of the low-level jet, an axis of instability up to 1000 J/kg of MLCAPE should be maintained for at least another couple of hours. With time, large-scale ascent and the low-level jet across Arkansas should weaken as the main short-wave trough moves away from the area. The weakening low-level jet should result in increased difficulty maintaining low-level instability. This combined with increasing convective inhibition from the loss of diurnal heating should result in a decrease in convective intensity through the evening hours. However, storm-scale processes (e.g. mesoscyclones) will allow thunderstorms to persist for at least a couple of hours into the less favorable environment. Thus, western Tennessee and Kentucky will be monitored for the need of a tornado watch. ..Marsh.. 04/21/2025 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...PAH...MEG...JAN...LZK...SHV... LAT...LON 36449104 36788802 33889070 33069332 36449104 MOST PROBABLE PEAK TORNADO INTENSITY...85-115 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
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