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Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
921 ACUS02 KWNS 261731 SWODY2 SPC AC 261730 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Fri Jul 26 2024 Valid 271200Z - 281200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL/EASTERN ND INTO FAR NORTHWEST MN... ...SUMMARY... Scattered severe thunderstorms are likely across portions of the northern Plains vicinity on Saturday. ...Synopsis... Upper troughing is expected to extend from the northern/central Canadian Prairie Provinces southwestward into northern/central CA early Saturday morning. Two primary shortwave troughs will be embedded within this troughing, one over the northern/central Canadian Prairies and the other over northern CA. Both shortwaves are expected to progresses east-northeastward throughout the day while losing amplitude. Eastward progress of this systems will be slowed by the Rex block downstream, with the southern cyclone initially over northeast OK/southeast KS and the northern anticyclone over Lake Michigan. This Rex block is forecast to break down under the influence of the western troughing, with the upper low drifting northeastward into southern MO and the upper ridge shifting eastward over the Lower Great Lakes by early Sunday. Surface pattern is forecast to feature an eastern CONUS ridge, initially centered over the Lower Great Lakes but extending southward into the Southeast. This ridging is expected to remain largely in place, while lee surface troughing sharpens across the High Plains and a cold front associated with the Canadian Prairie shortwave trough moves into the northern Plains. Thunderstorm development is anticipated along the cold front across ND Saturday evening. Storm development is also anticipated farther southwest across the central Rockies, with the resulting storms then tracking eastward into the central High Plains. ...Northern Plains.. Showers and thunderstorms will likely be ongoing early Saturday morning from the eastern Dakotas int northwest MN, remnant from overnight development across the western/central Dakotas. This activity will likely be weak, but cloud cover and associated outflow could act to provide the surface boundaries needed to provide the impetus for additional storms during the afternoon/evening. Large-scale forcing will be weak, but low-level convergence and ample low-level moisture could still result in thunderstorm initiation. Given the steep low-level lapse rates and high cloud bases, damaging gust will be the primary threat. Even so, some hail is possible with the early, more cellular storms. A tornado or two is possible as well if the boundary is sharp, with surface winds backing in its vicinity. Mesoscale factors will play a large role in determining the storm coverage and associated severe potential, which merits keeping low severe probabilities with this outlook given the forecast range. Farther east, thunderstorm development appears likely along the southeastward-progressing cold front expected to move across the western Dakotas during the late afternoon. Ample low-level moisture will support airmass destabilization despite strong mixing, and robust updrafts are likely within the initial development. Hail is possible early, with a quick transition to outflow-dominant structures anticipated. Highest coverage is expected across ND, which corresponds to the greatest severe thunderstorm potential as well. Storm longevity will be limited by the onset of nocturnal cooling, which should lead to relatively quick low-level airmass stabilization. ...Northern Great Basin into the central Rockies and central High Plains... A belt of enhanced mid-level flow is forecast to stretch from the base of the northern/central CA shortwave trough mentioned in the synopsis into the northern Plains. The CA shortwave is expected to progress northeastward throughout the period, with a subtle, convectively enhanced lead shortwave trough likely proceeding it across the central Rockies. Large-scale ascent attendant to these shortwaves coupled with increased mid-level moisture and deep boundary-layer mixing will support thunderstorms across much of the region, beginning over the higher terrain and then eventually spreading into the High Plains. Gusty outflow winds could accompany of any of the stronger, more persistent storms. Coverage of these strong storms may be high enough to merit greater severe probabilities in later outlooks. ..Mosier.. 07/26/2024 $$