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Friday, May 28, 2021

SPC May 28, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1259 AM CDT Fri May 28 2021 Valid 281200Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE SOUTHERN HIGH PLAINS AND MID ATLANTIC... ...SUMMARY... Widely scattered severe thunderstorms with large hail, gusty winds, and perhaps a tornado are possible this afternoon and evening in southwest Texas and southeast New Mexico. Widely scattered strong to severe thunderstorms associated with wind damage are also possible over parts of the Mid-Atlantic. ...Synopsis... A mid-level trough and associated surface low will move across the Ohio Valley and Mid Atlantic states this afternoon and evening as a cold front sags across the southeast states. At least scattered strong thunderstorms with some severe potential are expected ahead of the surface low across the Mid Atlantic, with more widely scattered storms expected down along the length of the cold front into the Southeast. Farther west, a mid-level trough will traverse the Northern Rockies as surface lee-troughing prevails across the northern High Plains, prompting isolated to scattered strong thunderstorm development by afternoon peak heating. Ridging aloft is expected through the day across the southern High Plains. However, the combination of upslope flow of a rich low-level airmass across the higher terrain, and differential heating along a draped cold front and convection-induced outflow boundaries, will support the development of scattered to numerous strong storms during the afternoon, with some organized severe possible. ...Southern High Plains... By mid to late afternoon, thunderstorms are expected to initiate off of the higher terrain of the Sacramento Mountains across eastern New Mexico, as well as along a northwest to southeast oriented outflow boundary/draped cold front region across southwest Texas. While relatively cooler, more stable conditions are expected east of the boundary, a very unstable airmass is expected immediately westward. Near 70 F surface dewpoints will be overspread by 8-9 C/km mid-level lapse rates, fostering up to 4000 J/kg MLCAPE in spots. Given modest surface-700 mb directional shear, along with appreciable speed shear above 600 mb, up to 50 kts of effective bulk shear may be achieved to the immediate lee of the higher terrain and in proximity to the aforementioned boundary, where locally higher (i.e. up to 150 m2/s2) effective SRH will reside. As such, discrete/semi-discrete supercells are expected, with large hail (some stones reaching above 2 inches in diameter) and occasional damaging gusts being the primary threats. However, any discrete supercell that can anchor to the boundary for an appreciable period of time may pose a tornado threat given the juxtaposition of very strong instability and locally higher effective SRH. The placement of the higher severe probabilities is highly dependent on the position of the boundary and may change in future outlooks. ...Mid Atlantic Region into the Southeast... Storms will develop/intensify ahead of the surface low and along/south of a warm front across portions of the Mid Atlantic, as well as along the cold front as the boundary layer destabilizes. While occasionally strong thunderstorms may immediately precede the cold front across the Southeast, greater shear and deep-layer ascent are expected across the Mid Atlantic, where a Slight risk has been maintained. Here, upper 60s F to 70 F surface dewpoints and up to 6 C/km mid-level lapse rates will contribute to 1000+ J/kg MLCAPE by afternoon peak heating. 40+ kts of effective bulk shear is also expected given moderate mid-level flow overspreading the region. Multicellular clusters capable of damaging gusts and occasional marginally severe hail are likely during the late afternoon/early evening hours. The strongest storms in close proximity to the warm front may also support a brief tornado given backed low-level winds and associated locally stronger low-level shear. ...Northeast Wyoming into Southeast Montana... Surface lee-troughing will support upslope flow along the lee of the Rockies, advecting up to 45 F surface dewpoints by afternoon. 8+ C/km low-level lapse rates along with the aforementioned low-level moisture advection will support up to 1000 J/kg MLCAPE into the early evening hours, when a belt of 40+ kts of 500 mb flow and effective bulk shear overspreads the region. As such, storms developing off of the higher terrain may become organized, with some of the stronger storms posing an isolated damaging gust/large hail threat given the steep lapse rates. ..Squitieri/Darrow.. 05/28/2021 Read more LIVE: spc.noaa.gov
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