SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1252 AM CDT Sun Jul 24 2022 Valid 241200Z - 251200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON AND EVENING ACROSS PARTS OF THE LOWER GREAT LAKES REGION INTO ST. LAWRENCE VALLEY... ...SUMMARY... Severe thunderstorms are expected to develop across the lower Great Lakes vicinity into St. Lawrence Valley by late this afternoon, accompanied by the potential to produce a couple of tornadoes, in addition to damaging wind gusts. ...Synopsis... Lower/mid tropospheric ridging appears likely to remain prominent from the subtropical western Atlantic through much of the southern tier of the U.S., with mid-level ridging also amplifying within the westerlies offshore of the British Columbia coast. Downstream of the building ridge, at least a couple of short wave troughs are forecast to dig to the lee of the Canadian and northern U.S. Rockies. Farther east, more prominent mid-level troughing, including a developing low, appears likely to continue to evolve to the south of Hudson Bay, across Ontario into Quebec and adjacent portions of the Great Lakes region into the Northeast. Within the evolving larger-scale cyclonic flow regime, models indicate that a convectively generated or enhanced lower/mid tropospheric jet streak will propagate into and across the lower Great Lakes region through St. Lawrence Valley by early evening, to the south of a deepening surface cyclone across western Quebec. A cold front trailing the cyclone appears likely to advance to the lee of the lower Great Lakes by late this evening, and through much of the middle Mississippi Valley and central Great Plains by late tonight. ...Ohio Valley/lower Great Lakes into northern New England... Remnant convective cloud cover and at least some precipitation may overspread much of the region during the day, initially inhibiting or slowing boundary-layer destabilization. However, in the wake of this activity, and generally aligned with the southwesterly to westerly jet streak (probably including 40-50+ kt speeds in the 850-700 mb layer), a corridor of substantive boundary-layer destabilization seems likely across the lower Great Lakes vicinity into St. Lawrence Valley, in response to low-level moistening and insolation. This may include mixed-layer CAPE on the order of 1000-2000+ J/kg, with higher values west-southwestward ahead of the front into a weakening flow regime across parts of the Ohio Valley by late this afternoon. In response to the destabilization, and forcing for ascent ahead of the larger-scale mid-level troughing, thunderstorms may initiate along and ahead of the lake breezes, where strong deep-layer shear and sizable, clockwise-curved low-level hodographs may become conducive to isolated supercells with the potential to produce tornadoes. Other storms are expected to form closer to the front across parts of southeastern Ontario (and into the Ohio Valley), with activity as whole tending to growing upscale, with the primary severe hazard transitioning to mainly potentially damaging wind gusts, before weakening by late evening while spreading east-southeastward. ...Montana into Colorado Rockies and adjacent plains... In the wake of the cold front to the lee of the Rockies, models indicate that moistening easterly/southeasterly near surface flow and daytime heating may contribute to areas of modest boundary-layer CAPE by late this afternoon, as lower/mid-tropospheric lapse rates steepen. Beneath modest west-northwesterly mid-level flow, particularly ahead of short wave digging across parts of the northern Rockies, this may become conducive to organizing convection posing at least some risk for severe wind and hail. ..Kerr/Weinman.. 07/24/2022
