Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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863 ACUS01 KWNS 212000 SWODY1 SPC AC 211959 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Fri Jun 21 2024 Valid 212000Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY...THE FOUR CORNERS REGION...AND SOUTHERN NEW ENGLAND... ...SUMMARY... Scattered strong to severe storms are expected from parts the upper Mississippi Valley into the northern High Plains, and into the Four Corners vicinity. A few strong storms may occur from parts of the Lower Great Lakes to southern New England. ...Discussion... Only two notable changes were made to the previous convective outlook. Otherwise the previous forecast thinking remains on track. 1) Have increased severe-wind probabilities to 15 percent and a categorical Slight Risk over southern portions of New England. Despite modest deep-layer westerly flow, steep 0-3 km lapse rates (7.5 to 8.5 deg C/km) and around 2 inches PW have yielded an environment that will favor multicells sporadically capable of strong to locally severe gusts (50-65 mph) and wind damage. A linear cluster near the NY/MA/CT border will likely push eastward over the next 2-4 hours and reach the CT/RI coast, and this area has been highlighted with recently issued Severe Thunderstorm Watch #444. 2) Included southwest NE in Slight-Risk equivalent severe wind probabilities based on the latest satellite/observational trends. Storms that potentially develop over the next few hours within southwest NE may yield a severe-wind hazard given the steep lapse rate environment. ..Smith.. 06/21/2024 .PREV DISCUSSION... /ISSUED 1052 AM CDT Fri Jun 21 2024/ ...Four Corners into WY... Water vapor imagery shows a well-defined upper trough over NV, with an associated 40+kt mid-level speed max tracking from northern AZ into UT/CO. Beneath this strengthening wind field and large-scale ascent, considerable low-level moisture is present today with dewpoints in the 50s across much eastern UT/western CO and southwest WY. Pockets of strong daytime heating will lead to scattered afternoon thunderstorms. Vertical shear profiles will promote supercell storm structures capable of hail and damaging winds for several hours this afternoon and evening. ...MT/WY... Several weak shortwave troughs are noted this morning moving east-northeastward across the northern Rockies. These features, combined with persistent easterly low-level winds across central/eastern MT will result in scattered afternoon thunderstorm development. Relatively isolated supercells are expected over MT, with more convective coverage farther south into eastern WY and western SD/NE. Storms will be capable of large hail and damaging winds, along with the possibility of a tornado or two (mainly over parts of MT). ...Central Plains... A well-defined surface boundary extends across northern NE into southern MN. Considerable heating to the south of this boundary, along with strengthening southerly low-level winds/convergence by late afternoon, will result in scattered thunderstorms in vicinity of the front. Sufficient flow aloft and ample CAPE will promote a risk of a few severe storms capable of damaging winds and hail. ...Lower MI... Pockets of strong heating will lead to scattered afternoon thunderstorms over parts of central and southern Lower MI. This area is along the southern fringe of stronger westerlies, with 25-30 knots of flow at 500mb. This might be sufficient for a few strong storms capable of gusty winds and hail. ...NY/PA/Southern New England... Hot and humid conditions are expected today across much of PA/NY and southern New England, with dewpoints in the 70s and temperatures well into the 80s and 90s. Mid level lapse rates are rather weak, so MLCAPE values will be <2000 J/kg. Given relatively weak winds aloft, thunderstorm organization is expected to be marginal. Nevertheless, a few strong storms capable of locally gusty/damaging winds are possible through the afternoon. Please refer to MCD #1352 for further details. $$