SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0253 PM CDT Sun May 23 2021 Valid 232000Z - 241200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL INTO NORTHERN HIGH PLAINS... ...SUMMARY... Scattered to numerous severe thunderstorms are still expected across a large portion of the High Plains this afternoon into evening. The most likely corridor for a few tornadoes, large hail, and significant severe wind is across northeast Colorado and western portions of South Dakota/Nebraska. ...20Z Update... No major changes have been made to the current Day 1 Outlook. Strong to occasionally severe storms have already developed along the CO Front Range, and additional thunderstorm development and intensification is still expected across much of the High Plains into the early evening hours. Storms will start off as initially discrete, with the potential to produce large hail (some significant) and perhaps a few tornadoes, especially from northeast CO northeastward, amidst backed, strengthening low-level flow. However, a relatively quick transition to linear convective modes will transpire, with damaging gusts becoming the primary concern from ND to the Trans Pecos region in southwest TX. While convection has struggled to organize thus far across portions of southern New England into the Mid Atlantic, surface temperatures have warmed into the 80s to near 90F, with 18Z RAP forecast soundings depicting a dry sub-cloud layer. As such, potential remains for a damaging gust into the early evening hours. ..Squitieri/Gleason.. 05/23/2021 .PREV DISCUSSION... /ISSUED 1136 AM CDT Sun May 23 2021/ ...Near Colorado Front Range/North-Central High Plains... On the southeast periphery of the prominent upper trough centered over the Great Basin/Intermountain West, a shortwave trough/speed max is readily apparent in water vapor imagery over the Four Corners area late this morning, and are likely to reach the north-central High Plains by around peak heating. Surface cyclogenesis will continue across the Nebraska Panhandle toward the Black Hills in vicinity of a northward-shifting warm front, while secondary surface cyclogenesis will also occur across southeast/east-central Colorado. A relatively moist air mass extends west-northwestward toward the Front Range/Black Hills with upper 50s/lower 60s F surface dewpoints. Moderately steep mid-level lapse rates of 7-7.5 C/km should support an increasingly expansive plume of moderate buoyancy with MLCAPE of 1000-2000 J/kg by peak heating. As pronounced mid-level height falls overspread the region this afternoon into evening and lingering cloud cover/inhibition quickly erode, thunderstorms will rapidly develop by early to mid-afternoon within a strengthening deep-layer shear regime. Supercells will be favored within the first couple hours of initiation, but a transition into one or more northeastward-moving QLCS are expected especially across westerns portions of South Dakota/Nebraska. Large hail will be likely mainly early, with severe wind gusts becoming the primary hazard as the aforementioned upscale growth occurs. A somewhat more focused tornado potential via a somewhat longer duration of discrete supercellular mode may exist across northeast/east-central Colorado into adjacent southwest Nebraska, although tornado potential will exist farther north in vicinity of the warm front even with a more mixed/transitional convective mode. ...Southern High Plains... Isolated to scattered thunderstorms are expected to develop this afternoon near the dryline, including near the Raton Mesa southward to the Trans-Pecos of far west Texas. A mix of supercells and multicell structures will be most favored in the Raton Mesa vicinity along the glancing periphery of the ejecting trough. Large hail, severe wind gusts, and a tornado or two are possible. ...Northeast States... Convective coverage will likely remain sparse owing to modest convergence along a predominately west/east-oriented cold front, which will be pushing south across the region this afternoon. Despite weak mid-level lapse rates, surface temperatures warming into the 80s amid upper 50s to low 60s dew points should support weak buoyancy with MLCAPE of 250-750 J/kg. Along the periphery of a mid-level speed max ejecting across northern Maine, adequate and nearly unidirectional deep-layer shear will exist for a few cells capable of producing locally damaging winds. Read more LIVE: spc.noaa.gov
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