Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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341 ACUS01 KWNS 211253 SWODY1 SPC AC 211252 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Fri Jun 21 2024 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY AND OVER THE FOUR CORNERS REGION... ...SUMMARY... Scattered strong to severe storms are expected from parts of the northern High Plains into the upper Mississippi Valley, mainly this afternoon and evening. Scattered strong/severe thunderstorms are also possible across the Four Corners vicinity. A few strong storms may occur from parts of the lower Great Lakes to southern New England. ...Northern High Plains... A shortwave trough will shift eastward from the Canadian Rockies toward Saskatchewan, with southeasterly low-level flow deep into Montana ahead of this shortwave trough. Relatively strong (40 kt) mid-level flow will develop across central Montana as the upper ridge flattens. Scattered robust convection should easily develop within a flow regime favorable for supercells. Forecast soundings, especially for central Montana, exhibit favorable deep-layer shear with strong buoyancy and relatively low cloud bases. Scattered supercells should evolve by early afternoon then propagate southeastward along the instability axis toward eastern/south-central Montana through early evening. Very large hail and gusty winds are expected along with some tornado risk. ...Middle Missouri Valley/Siouxland to Upper Mississippi Valley... Scattered thunderstorms persist this morning regionally in vicinity of the convectively modified frontal zone. A mid-level impulse over Colorado/southeast Wyoming this morning will reach the Siouxland by late afternoon and early evening, all while a south-southwesterly low-level jet markedly intensifies after sunset. Strong diurnal heating south of the boundary will ease CINH across the warm sector and scattered storms are expected to develop and intensify. Updrafts may initially develop along the cool side of the boundary but with time surface-based storms are expected. Hail, wind, and perhaps a couple tornadoes can be expected with supercells occurring near the front. ...Four Corners Region... A seasonally high PW plume will advance into the Four Corners region as a low-latitude shortwave trough over southern California/Nevada ejects over the Great Basin, strengthening mid-level flow across southern Utah into southwestern Colorado. Sustained multicells and some supercells should develop along the southern fringe of this shortwave trough, where strong shear will support organized longer-lived updrafts. Large hail and strong/gusty winds can be expected, and some tornado risk may exist as well. ...Lower Great Lakes to southern New England... Strong boundary-layer heating will once again occur across the lower Great Lakes region into portions of southern New England, with a southward-shifting front focusing scattered convection into early/mid-afternoon. Within a moderately unstable environment, localized wind damage will be the primary concern with the strongest storms his afternoon through around sunset. ..Guyer/Mosier.. 06/21/2024 $$