SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1127 PM CST Fri Jan 08 2021 Valid 091200Z - 101200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Scattered weak thunderstorm activity is possible this afternoon through tonight across parts of the southern Rockies into central and southeastern Texas, and perhaps near northern California coastal areas. ...Synopsis... Another initially vigorous short wave impulse, emerging from a strong mid-latitude Pacific jet, appears likely to progress into amplified branching flow across the eastern Pacific into western North America during this period. As it does, models indicate that it will weaken substantially and split, with one portion accelerating north-northeastward across the British Columbia coast, and another turning eastward, inland across the southern Oregon/northern California coast. It appears that this will be accompanied by a weakening surface front preceded by a moist plume emanating from the subtropical Pacific, though richer moisture return may become cut-off before reaching the Pacific coast. Downstream, and ahead of inland advancing mid-level ridging, the fairly vigorous southern portion of a preceding perturbation is forecast to dig across the southern Rockies into the Permian Basin by late tonight. Models suggest that this will be preceded by moisture return emanating from the southwestern Gulf of Mexico. However, this initial moistening is expected to be elevated above a cool and dry low-level environment. Beneath otherwise broadly confluent mid/upper flow across and east of the Rockies, cold surface ridging is forecast to prevail across much of the U.S., in the wake of a cyclone migrating northeastward away from the Mid Atlantic coast. This will maintain generally stable conditions across most areas, with negligible risk for severe thunderstorms. ...Texas... Particularly east of the Edwards Plateau and Hill Country vicinity, forecast soundings indicate that initial moistening will largely be rooted in the 850-700 mb layer. However, beneath modestly steep mid-level lapse rates, it appears that this may contribute to thermodynamic profiles marginally sufficient for weak convection capable of producing lightning. Aided by mid-level warm advection ahead of the approaching short wave impulse, this may initiate across parts of south central Texas into the middle Texas coastal plain this evening, before spreading northward and northeastward through tonight. Farther west, mid-level cooling in the exit region of the cyclonic jet accompanying the short wave impulse may contribute to scattered weak thunderstorms across parts of the Edwards Plateau and Hill overnight. ...New Mexico... The mid-level cold core of the digging short wave trough is forecast to overspread the higher terrain of northwestern through south central New Mexico today. This may contribute to weakly unstable thermodynamic profiles at least marginally conducive to convection capable of producing lightning this afternoon. ...Pacific Northwest... Latest model output suggests that the mid-level cold core with the splitting/weakening inland advancing perturbation may not be particularly cold, with richer moisture return becoming cut off before reaching coastal areas. This seems to limit the potential for thunderstorms. However, a couple of lightning flashes might still be possible late tonight across southern Oregon/northern California coastal areas, coincident with the stronger mid-level forcing for ascent. ..Kerr.. 01/09/2021
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