Severe Storm Outlook Narrative (AC)
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Issued by NWS
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792 ACUS01 KWNS 151631 SWODY1 SPC AC 151630 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Sat Jun 15 2024 Valid 151630Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS...AND THE MID MISSOURI VALLEY/CENTRAL PLAINS... ...SUMMARY... Scattered severe thunderstorms with damaging winds and large hail are possible from the late afternoon into the evening across the Mid-Missouri Valley, and also from eastern Montana to the western/central Dakotas. A few tornadoes could occur in eastern Nebraska and western Iowa, with isolated significant severe hail and wind possible across parts of the northern Plains. ...Northern Plains... A pronounced upper trough/low will progress eastward across the northern Rockies/High Plains and western Canada through the period. A related mid-level jet will begin to overspread the northern High Plains later this afternoon. This feature will contribute to strengthening flow aloft and increasing deep-layer shear to support organized severe thunderstorms. At the surface, a low should consolidate by early evening over eastern MT and the western Dakotas, with a cold front forecast to sweep eastward over the northern Plains this evening and overnight. Near and east of the surface low, around 1500-2500 J/kg of MLCAPE should develop through peak heating across parts of the western/central Dakotas, as a modestly moist low-level airmass continues to advect northward. Current expectations are for high-based thunderstorms to initially develop early this afternoon across parts of central MT as large-scale ascent preceding the upper trough overspreads this region. A well-mixed boundary layer combined with sufficient instability should encourage severe downdraft winds with any cluster that can form/persist with eastward extent. Isolated significant severe winds up to around 75 mph appear possible. The Slight Risk has been expanded westward some into more of central MT to account for this scenario. A somewhat separate area of convection may develop across the Bighorns of northern WY, and subsequently spread eastward across western/central SD through this evening with a threat for mainly severe/damaging winds. Any sustained supercells that can develop should pose a threat for large to very large hail given the favorable thermodynamic and kinematic environment present. This appears most probable across parts of western ND this evening, although there is still some uncertainty regarding what the dominant convective mode will be. A tornado or two may also occur across western ND and vicinity with any supercell that persists this evening as 0-1 km SRH gradually increases in tandem with a strengthening low-level jet. ...Mid Missouri Valley/Central Plains... Morning visible satellite and radar imagery show multiple MCVs across the central Plains and Mid MO Valley associated with prior convection. A shortwave trough will move eastward across these regions through the day, with modestly enhanced mid-level winds overspreading parts of NE/IA and vicinity. At the surface, a warm front will attempt to lift slowly northward over this region as well, but outflow from ongoing elevated convection in northern MO may slow its progress to some extent. This outflow boundary may also severe as an effective warm front and thunderstorm initiation zone this afternoon. Regardless, a gradually destabilizing airmass is anticipated across eastern NE through mid/late afternoon as filtered daytime heating occurs. Most guidance continues to suggest that around 2000-3000 J/kg of MLCAPE will develop in a narrow corridor along/near the warm front by 20-21Z, with steep mid-level lapse rates aiding in this development. Although deep-layer shear does not appear overly strong, it should be sufficient for a few supercells to develop initially. In addition to a threat for large hail with these supercells, a few tornadoes may also occur given the presence of a 30-35 kt southerly low-level jet and enhanced low-level SRH in the vicinity of the warm front. Some upscale growth could occur this evening, with a potentially greater severe/damaging wind threat with any small cluster that can persist into IA and perhaps southern MN. ...Southern High Plains... Isolated to scattered thunderstorms are forecast to develop this afternoon through early evening along/east of a weak surface trough/dryline across parts of the southern High Plains, including the OK/TX Panhandles southward to west TX. Weak to moderate instability and modest deep-layer shear should support some convective organization. Isolated severe wind gusts will be possible with a generally hot and well-mixed boundary layer, along with some potential for hail with the more robust cores. ..Gleason/Goss.. 06/15/2024 $$