SPC Aug 12, 2017 1630 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 12 Aug 12:42

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1133 AM CDT Sat Aug 12 2017 Valid 121630Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN/CENTRAL PLAINS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHEAST STATES... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE SOUTHERN PLAINS... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN/CENTRAL PLAINS... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHEAST/MID-ATLANTIC STATES... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE SOUTHERN PLAINS TO ARK-LA-TEX... ...SUMMARY... Scattered severe storms are expected across parts of the Great Plains and Northeast, mainly this afternoon and evening. The most intense storms should occur over western portions of South Dakota and Nebraska and eastern Colorado, with very large hail possible in these areas. ...Northern/Central Plains... A shortwave trough over eastern MT and ND at late morning will continue southeastward toward parts of the Upper Midwest through tonight, with a southern-peripheral belt of moderately strong mid-level westerlies overspreading the north-central Plains. Ahead of the lee trough/dryline, surface dew points in the middle 50s to lower 60s should reside with uninhibited insolation. Amid steep 700-500 mb lapse rates of 7-8 C/km, a corridor of 1000-2000 J/kg MLCAPE will develop from the central High Plains through western SD. Scattered storms will form near the shortwave impulse and south along the lee trough extending southward into far western NE and eastern CO. At least a few supercells are likely, capable of very large hail, locally severe wind gusts, and a brief tornado. As low-level southerlies increase during the evening, a couple of southeastward-moving clusters should form with the primary hazard shifting to severe wind and some hail. This activity will eventually weaken overnight given a rather stable air mass to the east over the lower Plains. ...Northeast/Mid-Atlantic States... A shortwave trough centered over southern Ontario will continue eastward today. Moderate diabatic heating of lower to middle 60s surface dew points ahead of the front should yield MLCAPE from 500-1500 J/kg. Although low-level winds should be weak, 35-45 kt mid-level southwesterly winds and nearly unidirectional winds with height will support moderately elongated, straight-line hodographs. As isolated to widely scattered storms form mid-afternoon, splitting cells should foster a risk for both severe hail and damaging wind gusts. ...Southern Plains toward Ark-La-Tex... Scattered showers/thunderstorms are prevalent across much of OK and northwest TX late this morning ahead of an eastward-moving MCV across the TX south Plains. Much of this precipitation/cloud cover will continue to reinforce a west/east frontal corridor, with the greatest diurnal destabilization expected across north TX where MLCAPE may exceed 2000 J/kg. Some rejuvenation of ongoing clusters could occur this afternoon in general vicinity of the Red River, while MCS redevelopment could also occur later this evening. Although some questions exist regarding the overall magnitude/extent of today's severe risk given the existing cloud cover and precipitation, will maintain a categorical Slight Risk at this time, mainly for localized damaging wind potential later this afternoon and evening. ..Guyer/Mosier.. 08/12/2017 Read more



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