SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1256 AM CDT Wed May 26 2021 Valid 261200Z - 271200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL PLAINS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE MODERATE RISK INTO THE SOUTHERN PLAINS AND ACROSS THE NORTHEASTERN US... ...SUMMARY... Severe thunderstorms will spread across the central Plains during the late afternoon and evening with a threat for large and destructive hail, very damaging winds, and tornadoes. Scattered severe is also expected across the southern High Plains and much of the northeastern US where damaging winds are the primary concern. ...Central/southern Plains... Early this morning a well-defined upper trough was located over eastern WA/OR. This feature is forecast to translate into eastern MT/WY by 27/00z with diffluent high-level flow expected to spread across the northern High Plains region during the afternoon. In response, a surface low should develop over southern WY by 18z then settle southeast along a frontal zone draped across the central Plains. Favorable low-level trajectories across KS/southern NE will force higher boundary layer moisture into the NE Panhandle prior to forecast maximum temperatures. In fact, isolated supercells will likely initiate across parts of eastern WY along the western fringe of higher-moisture content where large-scale forcing will be maximized. Latest thinking is boundary-layer heating will be most intense across southeast WY/southern NE Panhandle, south along the NM/TX border region. NAM forecast sounding for BFF at 21z exhibits around 3000 J/kg MLCAPE with surface-6km bulk shear on the order of 40kt. Environmental conditions appear very favorable for discrete supercells early in the convective cycle ahead of the surface low into northeast CO. With time, numerous supercell structures should grow upscale as they mature along/south of the aforementioned frontal zone. Very large hail will likely be noted with this early activity, and SRH values certainly suggest tornadoes will be a threat until storm mergers lead to a potentially significant MCS downstream over southern NE/northern KS. If an intense MCS does evolve, as seems possible, very damaging winds could be noted along the leading edge of this cluster as it surges east-southeast along the nose of a pronounced LLJ. Isolated severe thunderstorms will also develop south across the High Plains into west TX where strong afternoon heating will once again allow surface parcels to reach their convective temperatures by late afternoon. Modest southwesterly flow aloft will support supercells, and large hail/wind are the greatest risks along the southern dryline. ...Northeast... Moist plume characterized by PW values in excess of 1.5 inches currently extends across the lower MS/lower OH Valley into lower MI. Deep trajectories appear favorable for some of this moisture to be drawn northeast across the OH Valley into southern QC ahead of the primary front that will approach the international border by early evening. However, strong boundary-layer heating will be observed well ahead of the front where moisture content should be slightly drier, but noteworthy and sufficient for robust convection. Only minor changes have been made to earlier severe probabilities across this region and that is to extend the SLGT Risk south into VA where higher moisture content/stronger instability will be noted. Forecast soundings suggest scattered thunderstorms may develop across upstate NY, southwest across western PA into eastern OH by 16-17z as surface temperatures warm through the 70s to near 80F. This activity will then spread/develop east across the Hudson Valley into portions of New England. Farther south, surface temperatures should warm into the upper 80s across the Delmarva region and this higher buoyancy may result in a greater risk of hail from eastern PA into northern VA as thunderstorms develop a bit later during the mid afternoon. Otherwise, damaging winds will likely be the greatest risk with multicellular updrafts that intensify during the heat of the day ahead of the short-wave trough. ..Darrow/Wendt.. 05/26/2021 Read more LIVE: spc.noaa.gov
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