####018005794#### ACUS01 KWNS 021247 SWODY1 SPC AC 021246 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 AM CDT Thu May 02 2024 Valid 021300Z - 031200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF NORTHWEST...NORTH-CENTRAL AND CENTRAL TEXAS... ...SUMMARY... Strong to severe thunderstorms will be possible today from parts of the Upper Midwest to the southern Plains. The greatest potential appears to be over parts of northwest, north-central and central Texas, where large to very large hail, severe gusts and a couple tornadoes are possible. ...Synopsis... In mid/upper levels, a complex cyclone -- now over southern SK and eastern MT -- is forecast to move slowly and erratically eastward stride the international border, orbited by several shortwaves/ vorticity lobes. The most influential of those perturbations is apparent in moisture-channel imagery over eastern WY to northwestern CO. This feature is forecast to strengthen and pivot to the central/eastern Dakotas by 00Z, then across MN to northern WI and western Lake Superior around 2Z tomorrow. Meanwhile, broad west- southwest to southwest flow in mid/upper levels -- with mainly convectively augmented/modified embedded perturbations -- will cover the central/southern Plains States. MCVs are evident over western IA, central OK and southeast TX. These should move across the Mississippi Valley this afternoon/evening, toward the Upper Great Lakes, Ohio Valley and Tennessee Valley, respectively. At the surface, 11Z analysis showed a low near STJ, with cold front across northeastern to south-central KS, the northern/western TX Panhandle, and north-central NM. A dryline was drawn over the Llano Estacado near the TX/NM line, southward into the western Big Bend region. By 00Z, the low should reach western WI, with cold front over northern IL, central MO, southeastern KS, central/southwestern OK, to a weak low over west-central TX. The eastward-mixing dryline will be overtaken by the cold front from north-south, with a 00Z position from the southern low southward near DRT. By 12Z, the cold front should reach the northeastern IN/northwestern OH region, extending southwestward to near a PAH-LIT-DAL line, then as a stationary to warm front west-northwestward to central NM. ...Southern Plains to western Gulf Coast... A large area of precip and embedded areas of thunderstorms is moving eastward across eastern OK, northeast/east TX, and western LA, anchored by some strong thunderstorm clusters in the southeast TX/southwestern LA area. Isolated, marginally severe hail and/or gusts may occur for a few more hours. Behind that activity, an outflow boundary extends across south- central TX, the Hill Country and Concho Valley regions, to the Permian Basin. Northward-directed warm/moist advection and theta-e recovery will occur today over west-central/northwest TX east of the dryline, before being intercepted by the cold front over the northwest TX/southwestern OK region this afternoon. Farther northeast over most of OK, severe potential will be more isolated and conditional near the front, given the presence of partially modified MCS-outflow air instead of a relatively undisturbed Gulf boundary layer. Isolated to scattered thunderstorms are expected to develop near the dryline and along the front this afternoon, with the most favorable parameter space, greatest low-level convergence, and densest convective concentration for severe potential being in and near the "slight" area. The northern rim of the residual outflow boundary will diffuse and move into this region as well, providing a potential low-level vorticity source that may help to offset some flow weaknesses aloft in terms of supporting supercell organization. 30-40 kt effective-shear magnitudes are possible. Forecast soundings reasonably indicate modest low-level flow supporting nearly straight hodographs with both left- and right-moving cells possible. Strong lapse rates -- generally 7.5 to 8 deg C from surface through 400 mb -- and mid/upper 60s F dewpoints, will support a plume of 3000-4500 J/kg MLCAPE over much of northwest, west-central and south-central/ southwest TX ahead of the dryline. Large to very large hail is the greatest concern, though storm-scale processes and boundary interactions may favor a tornado threat as well. Upscale aggregation of some of this convection is possible, increasing the severe-gust potential for at least a few hours into this evening and tonight. ...Midwest... A band of initial convection is crossing portions of IA and northwestern MO, ahead of the surface cold front. As this activity moves eastward into weakly destabilizing parts of IL/WI/northern MO through the day, some intensification may occur, resulting in isolated damaging gusts and marginally severe hail from the strongest segments. Behind this activity and along/ahead of the cold front, modest destabilization (from warm advection and limited insolation) will occur, supporting isolated to widely scattered afternoon thunderstorm development along the front, and additional risk of gusts/hail near severe limits. Favorable deep shear (effective-shear magnitudes around 40-50 kt) will spread over the area. However, limited instability is expected, with modest deep- layer lapse rates and trajectories from convectively processed source regions, keeping MLCAPE generally in the 500-1000 J/kg range in a narrow prefrontal corridor. Activity should weaken in the evening as it moves into a more-stable airmass. ..Edwards/Leitman.. 05/02/2024 $$