SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1238 AM CDT Sun Aug 15 2021 Valid 151200Z - 161200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL PLAINS...ARIZONA...AND FLORIDA... ...SUMMARY... Isolated strong to severe storms with large hail and gusty winds will be possible mainly this afternoon and evening over parts of the central Plains and Arizona. An occasional strong wind gust and perhaps a tornado may also occur along the west coast of the Florida Peninsula today, and possibly part of the Florida Panhandle tonight. ...Central Plains... A modestly enhanced north-northwesterly mid-level flow regime is forecast to remain over the central Plains today. One or more subtle shortwave troughs may move southward across the Plains through the period and encourage convective development. Some morning storms may be ongoing at the start of the period across portions of central NE and north-central KS in a low-level warm advection regime. This activity could pose an isolated threat for marginally severe hail. Otherwise, additional storms may develop later this afternoon and early evening across a broader portion of the central Plains along and east of a surface lee trough. The presence of mid 50s to low 60s surface dewpoints and steep mid-level lapse rates emanating from an EML will likely promote around 1500-2500 J/kg of MLCAPE in a relatively narrow corridor as diurnal heating occurs. Weak southerly winds at low levels are forecast to veer strongly to north-northwesterly at mid levels, with 30-35 kt of effective bulk shear supporting some storm organization. Both multicells and marginal supercell structures appear possible. Isolated large hail and severe downdraft winds may occur with any storm that can form in this regime. At this point, uncertainty regarding storm coverage remains high, as large-scale ascent appears weak/nebulous. ...Arizona... Around 15-20 kt of east-northeasterly mid-level flow should be present over parts of northern/central AZ this afternoon on the southern periphery of an upper-level high centered over CA and the western Great Basin. There is some signal in short-term guidance that isolated to scattered storms will form over the higher terrain of this region and subsequently spread slowly west-southwestward towards the lower CO River Valley through at least the early evening. NAM forecast soundings show a very well-mixed boundary layer with some deep-layer shear and moderate instability by late afternoon. Isolated marginally severe hail and strong/gusty wind may occur with these storms before they eventually weaken tonight due to increasing convective inhibition from the loss of daytime heating. ...Florida... The remnants of Fred are forecast by the NHC to regenerate into a tropical cyclone at some point later this morning. Latest forecast track and most 00Z guidance suggest the enhanced south-southeasterly low/mid-level flow in the eastern half of Fred's circulation should remain mostly off the west coast of the FL Peninsula and parts of the FL Panhandle through the period. Still, there may be some potential for a strong wind gust or two across this region within an outer rain band. A brief tornado also cannot be ruled out. ..Gleason/Marsh.. 08/15/2021 Read more LIVE: spc.noaa.gov
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