Severe Storm Outlook Narrative (AC)
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Issued by NWS
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153 ACUS01 KWNS 202002 SWODY1 SPC AC 202001 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0301 PM CDT Thu Jun 20 2024 Valid 202000Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTH-CENTRAL HIGH PLAINS AND NORTHEAST/NEW ENGLAND...THE FOUR CORNERS...AND SOUTHERN LOWER MICHIGAN... ...SUMMARY... Storms may produce scattered damaging wind gusts over parts of the Northeast and New England mainly this afternoon. Scattered severe storms are also expected over parts of the north-central High Plains, the Four Corners, and southern Lower Michigan. ...20z outlook update discussion... The only changes made to the outlook are described below. Otherwise, no change was made to the previous outlook and forecast reasoning appears on track. ...Southern Lower Michigan... Surface boundary has become draped west to east across southern Lower MI with a reservoir of lower 70s deg F surface dewpoints immediately in the vicinity of the front. Surface streamline analysis indicates weak surface convergence and preferential storm development is expected along the boundary through the early evening. Strong to severe gusts (50-65 mph) capable of wind damage will be the primary hazard with the stronger water-laden downdrafts. The ongoing thunderstorm activity will likely slowly migrate east-southeast into southeast Lower MI towards early evening. ...Four Corners... The northwest periphery of seasonably high moisture will continue to support additional storm development through the early to mid evening across this region. The development of steep 0-3 km lapse rates and a wind profile promoting organized single cells/multicells and perhaps transient supercells, will foster a risk for severe gusts (60-75 mph) through the early to mid evening with the stronger microbursts. ...Northeast Colorado... Have expanded the Slight-Risk equivalent severe probabilities farther south-southwest to east of the Front Range north/northeast of Denver. Storms will move east of the higher terrain of the Front Range and potentially pose a risk for wind/hail with the stronger storms. ..Smith.. 06/20/2024 .PREV DISCUSSION... /ISSUED 1112 AM CDT Thu Jun 20 2024/ ...Eastern NY and New England... Visible satellite imagery shows strong daytime heating occurring across all of New England and parts of NY/PA. A well-defined MCV currently over eastern Lake Ontario will track eastward into this warm and very humid air mass (dewpoints in the low 70s), where afternoon MLCAPE values will exceed 2000 J/kg. Scattered to numerous thunderstorms are expected, with storms spreading eastward through the afternoon towards the coast of southern ME/NH/MA. Winds aloft are not particularly strong, suggest early activity may be rather disorganized. However, eventual congealing of outflow will likely result in locally damaging wind gusts. Hail will also be possible in the strongest cells. Please refer to MCD #1340 for further details. ...Central High Plains... Latest surface analysis shows south-southeasterly low-level winds across the NE Panhandle and southeast WY, where dewpoints are in the 50s and lower 60s. This will help maintain a moist/unstable air mass in the area, yielding afternoon MLCAPE values of around 1500 J/kg. Scattered thunderstorms are expected to form over southeast WY by 20z, where sufficient deep-layer shear and steep lapse rates will favor supercell structures capable of very large hail and perhaps a tornado. Storms will track eastward into the NE Panhandle and southern SD through the evening, with an increasing risk of damaging winds (possibly exceeding 65kt). ...Western CO... Moderately strong southwesterly low/mid-level flow is present today across western CO, where full heating and diurnal destabilization will occur. Morning models continue to show scattered or greater thunderstorms coverage this afternoon, in a deeply mixed environment. Several fast-moving high-based thunderstorms are expected, with a risk of locally severe winds in the stronger cores. $$