SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1259 AM CDT Sun May 23 2021 Valid 231200Z - 241200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER WESTERN SOUTH DAKOTA AND NORTHWEST NEBRASKA... ...SUMMARY... Severe thunderstorms capable of severe gusts, large hail and a few tornadoes are possible across portions of the central and northern Great Plains Sunday afternoon and evening. The most likely area for damaging winds and a few tornadoes is over western South Dakota and northwest Nebraska. ...Synopsis... Upper-level low pressure centered over the western U.S. will lift north/northeast Sunday, allowing a belt of stronger mid-level southerly flow to develop across the central/northern high Plains. An expansive ridge aloft centered generally along the MS River will shift east, while a fast-moving upper-level trough moves southeast over the northeast U.S./Canadian Maritime Provinces during the day. By 00z Monday, a surface cold front should extend west from near Long Island, NY, becoming a warm front over the northern Plains and to a low pressure area over western SD. A cold front will extend south from the low across eastern portions of CO/NM. ...Northeast CO/Western NE northward to Dakotas... As a surface low becomes better defined over western SD during the afternoon, strong southeasterly low-level winds will transport lower 60s surface dew points as far north as the ND/SD border. In the presence of mid-level lapse rates of near 7 deg C/km, MLCAPE should range from 1000-2000 J/kg. As strong height falls (60-90 m) overspread the High Plains, thunderstorms should develop rapidly by early/mid afternoon over northeast CO/far eastern WY. Supercells will be favored initially, with a quick transition into a northeast-moving linear convective system expected. Instances of large hail will be possible mainly early, with damaging winds becoming the primary hazard as upscale growth occurs. Short-range model guidance show impressive cold pool generation supporting an Enhanced categorical risk across western SD/northwest NE, with some adjustment possible in later outlooks as confidence increases in the northward movement/position of the warm front. The potential for a few tornadoes will exist with any storm in proximity to the surface low and warm front, where locally enhanced low-level SRH (200-300 M2/S2) will exist. Embedded QLCS circulations are also possible as the line matures during the late afternoon/evening. ...Central/southern High Plains... Widely scattered storms are expected to develop during the afternoon in the vicinity of a dryline over southeastern CO/eastern NM, and move into western KS/West TX and TX/OK Panhandles through early evening. Moderate instability and 25-35 kts of shear will support a mix of supercell and multicell structures initially with a risk for large hail and damaging gusts. A couple clusters or line segments may eventually evolve with damaging winds becoming more prevalent through the evening. ...Northeast U.S.... Low to mid 60s surface dewpoints will exist ahead of the cold front and, despite mid-level lapse rates averaging around 6 deg C/km, diurnal heating should contribute to MLCAPE of 500-locally 1000 J/kg. Isolated thunderstorm development is expected with the cold front, and moderate/strong and nearly unidirectional deep-layer flow will be sufficient for organized storms capable of strong/severe gusts as higher momentum aloft is lowered to the surface in the strongest downdrafts. ..Bunting/Wendt.. 05/23/2021 Read more LIVE: spc.noaa.gov
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