SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1125 PM CST Mon Jan 11 2021 Valid 121200Z - 131200Z ...NO THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk for thunderstorms appears negligible across the U.S. today through tonight. ...Synopsis... It appears that a perturbation within the persistent strong mid-latitude Pacific jet will undergo considerable amplification (near 160 W latitude) during this period. As it does, downstream ridging is forecast to build within the mid-latitude westerlies, and across the subtropical eastern Pacific. On the northeastern periphery of this ridging, models indicate that a vigorous short wave perturbation will accelerate east-northeastward toward the Pacific Northwest coast today, before turning eastward, inland near the international border area tonight. This may be accompanied by a developing surface frontal wave into coastal areas northwest of Puget Sound by this evening, and more prominent surface cyclogenesis to the lee of the Canadian Rockies by 12Z Wednesday. A plume of moisture (emanating from the lower latitude western Pacific) on its southern periphery will probably be shunted southward ahead of the cold front, becoming focused across northern California by the end of the period. Downstream, relatively dry and stable conditions are expected to generally prevail across much of the remainder of the U.S., with confluent mid-level flow contributing to the maintenance of cold surface ridging across much of the Gulf Coast states and northwestern Gulf of Mexico. Models suggest that the frontal zone marking the leading edge of this air mass will stall across southern portions of the Florida Peninsula and the southern Gulf of Mexico, along and south of which seasonably high moisture content likely will remain confined. ...South Florida/Keys... Although there may be some further boundary-layer moistening along/ahead of the initially southward advancing cold front, showers associated with moistening and forcing for ascent aloft probably will tend to stabilize lapse rates and minimized boundary-layer destabilization. While a brief, weak thunderstorm or two might not be entirely out of the question, it is not yet clear that probabilities meet the minimum 10 percent threshold. ...Parts of south central Texas into lower Mississippi Valley... Within remnant mid-level troughing gradually emerging from the northern Mexican Plateau and adjacent southwest Texas, a compact embedded mid-level low is forecast to track near/south of the Hill Country toward the lower Mississippi Valley today through tonight. Although this is well to the cool side of the surface frontal zone, forecast soundings indicate that, near the base of steeper mid-level lapse rates beneath the mid-level cold core, elevated moisture return may contribute to weak CAPE supportive of scattered high-based convection. Much of this is currently forecast to remain above the freezing level, and probabilities for weak thunderstorms are being maintained at less than 10 percent. However, sporadic lightning with convection may not be entirely out of the question along the track of the low. ...Pacific Northwest... Strong mid-level cooling may not spread inland across northwestern Washington until after 13/06Z this evening, and the extent to which thermodynamic profiles become conducive to convection capable of producing lightning remains unclear, based on latest forecast soundings. While sporadic lightning appears possible, mainly near the international border to the west of the Cascades, probabilities still appear less than 10 percent. ..Kerr.. 01/12/2021
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