Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
755 ACUS02 KWNS 261732 SWODY2 SPC AC 261730 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Wed Jun 26 2024 Valid 271200Z - 281200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN MONTANA...THE WESTERN DAKOTAS...FAR NORTHEAST WYOMING...WESTERN NEBRASKA...AND EXTREME NORTHEAST COLORADO... ...SUMMARY... Severe thunderstorms producing gusts to 80 mph, large hail greater than 2.5 inches, and a couple of tornadoes are possible across parts of eastern Montana into western portions of the northern and central Plains Thursday afternoon and evening. ...MT/ND/SD/NE vicinity... An upper ridge will initially be positioned over the northern High Plains vicinity on Thursday. The ridge will flatten and shift east through the period as an upper shortwave trough over the Pacific Northwest develops east across the northern Rockies. Strong height falls will result in a deepening surface low over eastern MT during the day. The low will develop east/southeast into the western Dakotas during the evening while an associated surface cold front shifts east across the region into the overnight hours. A surface trough/dryline will extend southward from the low across the northern/central High Plains. South/southeasterly low-level flow will transport 60s F dewpoints northward across KS/NE and into the Dakotas/eastern MT. Cooling aloft/steepening midlevel lapse rates atop this moist boundary-layer will result in a corridor of moderate to strong instability. Vertically veering wind profiles indicate supercells storm mode will be possible with initial convection developing during the afternoon. Initial storms are likely to first develop over higher terrain and near the surface low in MT, and southward along the dryline in an area of strong low-level convergence and increasing large-scale ascent. With time, a southerly low-level jet is forecast to increase during the evening. Thunderstorm clusters may grow upscale into a coupe of smaller bowing MCSs from far eastern MT/western Dakotas, and possibly across western NE. Large instability, a deeply mixed boundary layer with steep low-level lapse rates, and some dry air above 700 mb will support strong downdrafts capable of severe to significant wind gusts. Isolated to widely scattered large to very large hail (2.5+ inch diameter) also will be possible, especially with any discrete supercells. As the low-level jet increases toward evening, low-level SRH will increase and hodographs will become enlarged, especially near the surface low. A few tornadoes will be possibly, mainly in the 23-03z time frame. Severe potential will gradually wane with eastward extent overnight as capping increases across central/eastern ND/SD/NE. ...Eastern CO/KS into the southern High Plains/northwest OK... Vertical shear will be more marginal (20-30 kt effective shear magnitudes) with stronger deep-layer flow remaining displaced northward. Nevertheless, a narrow corridor for rich boundary-layer moisture and strong instability will exist along/just east of the surface dryline. Isolated/widely scattered thunderstorm activity is expected by late afternoon into the evening. Transient supercells capable of mainly strong/severe gusts and hail will be possible during the afternoon/evening. Clustering may occur during the evening over KS as the low-level jet increases, but strong capping with eastward extent will likely limit severe potential overnight. ...UT/AZ/NM/western CO/WY... A relatively moist airmass will be in place, with surface dewpoints in the upper 40s to upper 50s F common across the region. This will aid in afternoon destabilization, with MLCAPE up to 750 J/kg forecast. Vertical shear will support at least transient organized cells as the area remains on the southern fringe of stronger mid/upper westerly flow. Isolated strong to severe gusts and marginal hail will be possible with storms during the afternoon into mid-evening. ...Eastern Carolinas/Southeast vicinity... Modest upper troughing will be oriented over the Southeast on Thursday. A weak surface boundary may sag southward across the Carolinas/GA while some forecast guidance indicates an MCV may be located over AL. A very moist airmass will be in place, and strong heating will aid in a corridor of moderate to strong instability. The most likely area for a few strong to severe storms will exist over the eastern Carolinas where strongest instability will align with modest vertical shear (around 25 kt effective shear magnitudes). Damaging gusts and isolated hail to near 1 inch diameter will be possible. Further west across parts of GA and AL, vertical shear will be very weak (less than 15 kt). This should preclude organized severe potential further west, but PW values greater than 2 inches and sufficient instability could result in a couple of strong gusts. ..Leitman.. 06/26/2024 $$