Severe Storm Outlook Narrative (AC)
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Issued by NWS
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824 ACUS01 KWNS 040554 SWODY1 SPC AC 040553 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1253 AM CDT Thu Jul 04 2024 Valid 041200Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER MISSISSIPPI VALLEY AND FROM THE MISSOURI OZARKS INTO THE SOUTHERN PLAINS... ...SUMMARY... Severe thunderstorms will be possible across parts of the Upper Mississippi Valley, Ozarks, and southern Plains. ...Discussion... Seasonally strong upper trough is shifting east across the northern Plains early this morning. This feature is forecast to advance toward the middle MO Valley by late afternoon as 500mb, 60kt speed max translates across southeast NE into IA. Left exit region of this speed max will spread across the upper MS Valley along with a corridor of modest 12hr mid-level height falls. Latest model guidance suggests a weak surface low will develop and track along the MN/IA border into southwest WI by late evening. This corridor appears favorable for robust convective development as boundary layer warms and convective temperatures are breached, likely by midday, as readings warm through the upper 70s-80F. Forecast soundings exhibit veering wind profiles with height, and some supercell potential exists within this zone of focused ascent. Large hail and locally damaging winds are the primary concerns. Farther south, an expansive corridor of convection has evolved over the central Plains early this morning. Upscale growth may continue for the next few hours, and a long-lived MCS should propagate across eastern KS into MO by sunrise. While this complex may not be particularly severe at daybreak, a long-lived MCS, or its remnants, will advance downstream into the OH Valley as modest mid-level flow will extend along a corridor from MO into southern OH. Models are not too aggressive in steepening low-level lapse rates east of the MS River later today, but some surface heating is expected to contribute to increased buoyancy that will likely contribute to new robust updrafts developing along the MCS outflow/differential- heating zone. Will maintain MRGL risk across this region, although somewhat higher severe probabilities may be warranted, especially across KY along the southern flank of the forward-propagating MCS. Later in the day, very strong surface heating across the southern Plains will result in steep surface-3km lapse rates from northwest TX, across central into northeast OK. As the northern Plains trough shifts east, mid-level flow will begin to turn more westerly across northern OK, and 500mb speeds will increase to 25-40kt north of I-40. Convective temperatures will be breached by 22z, just ahead of the surface front, and scattered thunderstorms should easily develop along the wind shift. PWs will be very high across this region with values in excess of 2 inches. With temp/dew point spreads around 30F, there is increasing confidence that the most robust convection should generate severe downdrafts. A fairly concentrated corridor of convection should evolve downstream into the MO Ozarks by early evening. ..Darrow/Squitieri.. 07/04/2024 $$