SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Mon Jun 19 2023 Valid 201200Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL GULF COAST STATES...AND THE NORTHERN PLAINS... ...SUMMARY... Isolated to scattered severe thunderstorms appear possible across parts of the Southeast and northern Plains on Tuesday. Damaging winds and large hail should be the main threats. ...Southeast... A weak closed mid/upper-level low is forecast to be centered over KY/TN Tuesday morning. This feature should move little through the period while remaining over the Southeast. Modestly enhanced mid-level north-northwesterly flow should be in place on the southwest flank of the upper low, and to the east of upper ridging across the southern Plains. Although there are still some differences in guidance, there may be some elevated thunderstorms ongoing Tuesday morning across parts of the ArkLaTex, posing mainly an isolated hail threat. Additional intense thunderstorm development should occur Tuesday morning through early afternoon along/south of a front draped from northern LA into southern MS/AL. Where robust diurnal heating can occur, moderate to strong instability will likely develop, as a very moist low-level airmass remains in place south of the front. Modest low-level winds are forecast to veer and strengthen with height through mid/upper levels. 30-40+ kt of deep-layer shear will support organized convection, with a mix of multicells and supercells possible initially. Isolated large hail may occur with any discrete convection, but most guidance suggests that thunderstorms will quickly form into one or more small bowing clusters as they spreads generally southward across LA and coastal/southern MS/AL through Tuesday afternoon. Accordingly, damaging winds will probably be the main threat with this activity as low-level lapse rates steepen through the day. Isolated strong to severe thunderstorms may occur farther east across south GA/north FL, and much of the FL Peninsula. However, deep-layer shear should be weaker with eastward extent, which should tend to limit the magnitude of the severe threat. ...Northern Plains... An upper trough/low will extend across much of western Canada and the northwest U.S. Tuesday. A 50+ kt southwesterly mid-level jet should be present from the Great Basin to the northern Rockies and adjacent High Plains, with upper ridging located from the southern/central Plains to the Upper Midwest. A surface cold front is forecast to be in place from the Dakotas into central Canada. A narrow corridor of mid to upper 60s dewpoints should exist near this boundary. As daytime heating occurs, a small zone of moderate to strong instability should develop near the front from parts of western/central NE into central SD and central/eastern ND. Various NAM/RAP forecast soundings across this area show steep mid-level lapse rates will contribute to considerable CAPE in the hail growth zone aloft. Even though stronger mid-level winds and related deep-layer shear will likely remain displaced to the west of greater forecast instability, there should be enough overlap to allow for some updraft organization. Mainly multicells should develop and spread generally north-northeastward through Tuesday afternoon/evening, while posing a threat for severe/damaging downdraft winds and some hail. There also appears to be some potential for a supercell and/or small bowing cluster behind the front from northeastern WY and southeastern MT into the western Dakotas. Stronger mid-level flow and deep-layer shear will be present across these regions, but instability is forecast to remain modest. Based on the consensus of high-resolution guidance, have expanded the Marginal Risk for hail/wind westward into these areas to account for this possibility. ..Gleason.. 06/19/2023
