Aggregator | disasterassistance.gov

SPC Aug 7, 2019 0730 UTC Day 3 Severe Thunderstorm Outlook

5 years 11 months ago

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0234 AM CDT Wed Aug 07 2019 Valid 091200Z - 101200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTHERN AND CENTRAL PLAINS...AND ACROSS PARTS OF OR INTO SOUTHEAST WA AND NORTHWEST ID... ...SUMMARY... Strong to severe thunderstorms are possible across portions of the northern and central Plains Friday afternoon and evening. Additional strong storms are possible across parts of the Pacific Northwest. ...Northern and Central Plains... The upper ridge will meander eastward over the Plains on Friday. A couple of shortwave impulses will float through the ridge in northwesterly deep-layer flow. The first ejects eastward from the northern Rockies as an upstream upper trough begins to move inland over the Pacific Northwest. This impulse will aid in weak surface cyclogenesis over the western Dakotas. Strengthening low-level south/southeasterly flow will transport low to mid 60s surface dewpoints northwestward into far eastern MT/WY/CO and across parts of the Dakotas/NE/KS. Strong heating will lead to moderate/strong destabilization by early afternoon with steep midlevel lapse rates in place beneath the upper ridge. Forecast soundings suggest shear profiles capable of supporting rating updrafts and large hail will be possible with initial storms from eastern MT/WY toward western ND/SD. Some tornado threat cannot be ruled out in the vicinity of the surface low where backed low level flow will maximize SRH coincident with mean mixing ratios approaching 14 g/kg. A 40 kt south/southwesterly low level jet is then forecast to increase during the evening and overnight hours, which could lead to upscale growth and increase in damaging wind potential across parts of SD. Given several periods of convection in days leading up to Friday and model differences in exact location of surface features, will introduce Marginal severe probs at this time, though upgrades in subsequent outlooks are possible. Further south, convection will develop over the higher terrain in CO. As convection moves off of higher terrain, high-based cells could produce hail and possibly strong gusts. However, the threat appears more conditional southward across eastern CO into parts of southeast WY and NE where capping may be stronger. Additionally, forecast soundings show weak midlevel flow, which could hinder storm organization/longevity of intense updrafts. ...Pacific Northwest... Thunderstorms will develop during the afternoon ahead of an upper shortwave trough moving onshore and a surface cold front moving inland during the evening. Modest boundary layer moisture with dewpoints in the upper 40s to low 50s and strong heating will result in MLCAPE values as high as 1500 J/kg with inverted-v thermodynamic profiles beneath the cloud bases. Strong southwesterly deep layer flow and effective shear values greater than 40 kt will lead to fast moving storms capable of strong downburst winds. Additionally, steep midlevel lapse rates could result in marginally severe hail. ..Leitman.. 08/07/2019 Read more