WeatherWheeler35 Posted May 20 Share Posted May 20 SPC AC 201948 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0248 PM CDT Sat May 20 2023 Valid 202000Z - 211200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTHWEST...THE RIO GRANDE VALLEY AND THE DEEP SOUTH... ...SUMMARY... Isolated and marginally severe thunderstorms are possible through this evening across parts of the Deep South, the Northwest, and the Rio Grande Valley. ...20z Update... Only minor adjustments have been made to the Marginal risk (level 1 of 5) across Deep South Texas and MS/AL. These changes are based on currently location of ongoing convection and the position of the surface cold front. Otherwise, the previous forecast is on track. For more details, see the 1630z Day 1 discussion below. ..Leitman.. 05/20/2023 .PREV DISCUSSION... /ISSUED 1126 AM CDT Sat May 20 2023/ ...Deep South... A low-amplitude shortwave trough over the Mid-MS Valley will move southeast towards the southern Appalachians, and will be preceded by an MCV currently centered on middle TN. Abundant cloud coverage across northern portions of AL/GA will limit boundary-layer destabilization to the immediate southeast of lingering stratiform rain attendant to the MCV. Amid poor mid-level lapse rates (5-5.5 C/km between 700-500 mb) sampled by the 12Z BMX/BNA soundings, the lack of more robust boundary-layer heating will likely mitigate appreciable severe potential with north/east extent. With more robust insolation underway farther south-southwest and richer boundary-layer moisture, a plume of moderate MLCAPE from 1500-2000 J/kg is anticipated across southern MS to central AL. This should support convective development trailing southwestward along/ahead of a southeast-moving cold front in the next few hours. With a predominant westerly deep-layer wind profile, effective bulk shear should be limited to around 20-25 kts where buoyancy is greater. Given the poor mid-level lapse rates upstream, hail sizes will probably remain small to marginally severe. A threat for isolated damaging winds should be the main hazard with multicell clusters that spread east-southeast and largely weaken after sunset. ...OR/WA... Somewhat greater convective coverage is anticipated relative to yesterday during the late afternoon and evening within a modest south-southwesterly deep-layer flow regime. The most likely corridor for scattered storm development is off the higher terrain in southern OR east of the Cascades, with more isolated activity possible across central WA. Where adequate effective bulk shear is present, largely close to the Cascades, marginally severe hail will be possible. Otherwise, isolated strong gusts will be possible in eastern OR given deeper mixed thermodynamic profiles with eastern extent. ...Southwest NM vicinity... A minor upper low persists near the northwest Sonora/southeast AZ border area and will drift north-northeast today. With low 50s surface dew points having spread west of the Rio Grande following a recent cold front intrusion, a pocket of weak buoyancy should develop with MLCAPE of 500-1000 J/kg. Effective bulk shear will likely remain weak, from only 20-25 kts as stronger speed shear is confined to the very upper portion of the buoyancy profile. Small to marginally severe hail and a few locally strong gusts cannot be ruled out. ...Deep South TX... A few strong storms remain possible later this afternoon as a cold front continues to move slowly southward. Buoyancy should remain moderate owing to broken cloud coverage ahead of the front. 0-6 km winds will remain unremarkable with moderate southwesterlies above that. In addition, mid-level lapse rates peaked this morning and are consistently progged to weaken through the day. Small to marginally severe hail and a few locally strong gusts cannot be ruled out. CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z Quote Link to comment Share on other sites More sharing options...
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