SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0220 AM CST Tue Feb 23 2021 Valid 251200Z - 261200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk for severe thunderstorms appears negligible across the U.S., Thursday through Thursday night. ...Discussion... Models indicate that a large, blocking ridge, centered at mid-levels over the southern mid-latitude eastern Pacific (between 140-160 W), may reach peak prominence during this period. It appears likely to remain in phase with large-scale ridging within the westerlies, which may continue to build north of the Aleutians and through the Gulf of Alaska. Intensifying mid-level flow on the northeastern periphery of this feature will take on an increasing northwesterly component near the British Columbia coast into the northern U.S. intermountain region, with a broad area of stronger mid-level height falls on the leading edge of this regime. In response to these developments, models indicate that a vigorous short wave impulse, initially near the southern Rockies, within the southern branch of split westerlies, will accelerate east-northeastward across the southern Great Plains and Ozark Plateau vicinity by 12Z Friday. However, this will be preceded east of the Rockies by the development of fairly expansive cold surface ridging across much of the Great Plains through the Ohio and Tennessee Valleys. And models indicate that any associated wave development, along the front demarcating the leading edge of this air mass across southeast Texas through the lower Mississippi Valley, will be weak. A continuing southerly return flow in advance of this wave may support a weak to modest influx of moisture off the northwestern Gulf of Mexico. In the wake of the wave, it appears that the shallow leading edge of the cold air will nose south of the Texas Rio Grande River vicinity, and into the western Gulf of Mexico, by the end of the period. ...Gulf States... Models suggest that stronger mid/upper forcing for ascent will be focused above/well to the cool side of the initially stalling low-level frontal zone. This is expected to overspread parts of north central and northeast Texas late Thursday afternoon, before developing east-northeastward into the vicinity of the southern Appalachians by late Thursday night, with warm layers aloft capping moisture return to the south. Associated destabilization is forecast to remain weak, but sufficient to contribute to thermodynamic profiles supportive of thunderstorm development. This may coincide with a strengthening west-southwesterly jet to 40-50 kt in the 850-700 mb layer, but with the core of this feature also focused above a substantive surface-based stable layer, the risk for severe weather appears negligible (particularly given the weak CAPE evident in the forecast soundings). ...Columbia Plateau vicinity... Large-scale ascent and strong mid-level cooling (500 mb temps to -30 to -35 C) accompanying the vigorous digging short wave may contribute to thermodynamic profiles supportive of convection capable of producing lightning, mainly Thursday afternoon. ..Kerr.. 02/23/2021
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