Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
174 ACUS02 KWNS 040541 SWODY2 SPC AC 040540 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1240 AM CDT Sat May 04 2024 Valid 051200Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN PLAINS INTO THE ARKLATEX AND LOWER MISSISSIPPI VALLEY...AND PORTIONS OF OHIO INTO WESTERN PENNSYLVANIA... ...SUMMARY... Isolated strong to severe thunderstorms may occur Sunday across parts of the southern Plains into the ArkLaTex and lower Mississippi Valley, and separately over portions of Ohio into western Pennsylvania. ...Synopsis... A pronounced/deep closed upper low over CA/NV will move eastward over the western states on Sunday, eventually transitioning into an open wave as it overspreads the northern/central Rockies by early Monday morning. A weak southern-stream shortwave trough is forecast to move northeastward from the southern Plains to the ArkLaTex and lower MS Valley through the day. Another upper trough over Ontario is expected to advance into Quebec, with the southern portion of this feature glancing the lower Great Lakes and vicinity. Surface lee cyclogenesis will occur across the northern High Plains ahead of the western CONUS upper trough/low. Rich low-level moisture should advance northward across the southern/central Plains through the period, although convection over TX may temporarily slow this process. ...Southern Plains into the ArkLaTex/Lower Mississippi Valley... Multiple thunderstorm clusters will probably be ongoing across parts of west into central TX at the start of the period Sunday morning. An isolated threat for damaging winds and hail may persist with this activity as it spreads eastward towards the middle/upper TX Coast through early Sunday afternoon. A gradual uptick in convective coverage and intensity may occur as modest destabilization occurs ahead of ongoing thunderstorms. Strong deep-layer shear should support continued convective organization, with small bowing clusters possible. Isolated strong to severe thunderstorms may also occur across parts of the ArkLaTex into the lower MS Valley as a weak shortwave trough moves across these regions through Sunday afternoon. However, effective bulk shear should remain weaker over these areas. Based on the likelihood and probable placement of morning convection across central TX, have expanded the Marginal Risk a bit southward/eastward, while also trimming much of north TX and south-central OK out of severe probabilities. ...Ohio into Western Pennsylvania... Modest destabilization should occur ahead of a weak front advancing east-southeastward across the OH Valley on Sunday. Isolated to scattered thunderstorms should develop by Sunday afternoon along or just ahead of this boundary, as weak large-scale ascent associated with an upper trough over Ontario/Quebec overspreads this region. Deep-layer shear of 20-30 kt should support marginal updraft organization. Occasional strong to damaging winds may occur with any small clusters that can consolidate and spread east-southeastward across parts of OH into western PA and vicinity Sunday afternoon and early evening. This activity should gradually weaken through the evening across PA as it encounters a less unstable airmass. ...Northern High Plains... Low-level moisture is expected to remain very shallow/meager across the northern High Plains through the period. Even so, daytime heating and steep mid-level lapse rates may still support weak instability developing through Sunday afternoon along/east of the sharpening surface lee trough. While isolated high-based convection that develops across this region could produce locally strong/gusty winds, the overall severe threat appears too limited to include low severe probabilities at this time. ..Gleason.. 05/04/2024 $$