SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1130 PM CST Tue Dec 15 2020 Valid 171200Z - 181200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Aside from parts of the Sierra Nevada Thursday morning, the risk for thunderstorm activity appears negligible across the U.S. the remainder of Thursday through Thursday night. ...Synopsis... Much of North America will remain under the general influence of belts of westerlies branching downstream of a strong mid/upper jet across the western and central, southern mid-latitude Pacific. Models indicate that these will remain largely zonal through this period, but with a number of modestly amplified and progressive short wave troughs. In association with one of these features, a significant surface cyclone is expected to be in the process of migrating east-north of the northern Mid Atlantic coast early Thursday, with a trailing cold front advancing through the remainder of the southeastern Gulf of Mexico and Florida Peninsula during the day. In their wake, cool surface ridging likely will prevail across much of the Gulf of Mexico, with only modest boundary layer moistening over the southwestern Gulf. Thus, despite strengthening southerly low-level flow forecast through the Great Plains, coincident with deepening surface troughing to the lee of the Rockies, there appears negligible potential for appreciable low-level moistening and destabilization. ...Parts of the northern Sierra Nevada... Preceded by an influx of moisture, within a narrow plume emanating from the southern mid-latitude/subtropical Pacific, a vigorous short wave impulse is forecast to dig inland of the northern California coast by 12Z Thursday. It appears that this will be accompanied by an 80-90 kt cyclonic mid-level jet (around 500 mb), with strong cooling and forcing for ascent in its left exit region spreading southeast of the San Francisco Bay area into portions of the northern Sierra Nevada Thursday morning. This may contribute to sufficient destabilization to support low probabilities for convection capable of producing lightning, particularly where aided by orographic lift across the Sierra Nevada. ...Southern Florida... Although weak boundary-layer CAPE may develop ahead of the southeastward advancing cold front, particularly across southeast coastal areas, weak low-level convergence and warm layers aloft (especially near/above 500 mb) appear to preclude an appreciable risk for thunderstorm Thursday. ..Kerr.. 12/16/2020
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