1PM Day 3 Convective Outlook for Saturday, March 7. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM TX TO LOWER MS VALLEY AND THE UPPER OH VALLEY TO LOWER GREAT LAKES
SUMMARY
Isolated to scattered severe thunderstorms are possible from Saturday morning into the evening across a broad swath of the southern Great Plains to the Lower Great Lakes. Isolated very large hail may occur in parts of Texas.
Synopsis
An upper trough consisting of multiple embedded shortwave impulses will move east from the Upper Midwest to the Great Lakes. A closed low over the Lower CO Valley will further retrograde to west of Baja CA. A surface cyclone over eastern Upper MI at 12Z Saturday will deepen as it rapidly progresses into QC. A full-latitude cold front will arc southwestward, crossing the eastern Great Lakes and Midwest on Saturday. The trailing portion will slow its southern movement over TX and likely be modulated by convective outflows.
TX to the Lower MS Valley
Primary changes are to add a CIG1 area for very large hail potential in TX, and shift/expand the cat 2-SLGT risk north-northeast per latest guidance.
While TX will largely remain within a flat to low-amplitude mid-level ridge between the aforementioned troughs/lows well to its north and west, seasonably rich low-level moisture atop an undercutting cold front should support regenerative convection through much of the period. With the west-southwesterly mid-level flow regime, steep mid-level lapse rates will be maintained over the pre-convective warm sector. Low-level flow will become increasingly weak and diffluent, yielding a favorable deep-layer wind profile for hail growth. Primary uncertainty is the degree of surface-based development towards late afternoon/early evening along the composite front/outflow. Current indications are that CIG2-type giant hail potential might evolve with more discrete/isolated convection in the south-central TX vicinity. For now, will incrementally add a CIG1 and defer to later outlooks for a possible categorical upgrade.
Farther east-northeast across the Lower MS Valley, clusters may be consolidating into line segments by mid-late morning Saturday. These may yield an increase in mainly damaging wind and brief tornado potential as the warm/moist sector destabilizes downstream. An extensive swath of widespread convection is anticipated during the afternoon. But this should become increasingly aligned with the deep-layer shear vector. In conjunction with decreasing low-level hodograph curvature, setup may only favor sporadic damaging winds before storm intensities wane after sunset.
OH Valley to the Lower Great Lakes
No adjustment has been made to the level 2-SLGT risk area. At least scattered convection should be ongoing upstream over parts of the Midwest and Mid-South along/ahead of the aforementioned cold front. This activity may not entirely decay, with renewed storm development possible along the large-scale outflow that will probably remain displaced appreciably east of the front. Where adequate insolation can occur amid steep mid-level lapse rates, an uptick in storm intensity should occur midday into the afternoon. Overall amplitudes still seem to favor non-significant severe, but a scattering of damaging winds, a couple tornadoes, and isolated marginally severe hail all appear plausible. These threats should wane after sunset and with eastern extent towards the Appalachians.