SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0632 AM CST Tue Dec 01 2020 Valid 011300Z - 021200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are not expected through tonight. ...Synopsis/Discussion... In mid/upper levels, a highly amplified pattern will continue through the period, but with considerable geometric change. A large cyclone -- initially covering much of the eastern CONUS and centered over western PA -- is forecast to move north-northeastward through 12Z tomorrow, with its 500-mb low reaching southern QC. The associated surface occluded front extended at 11Z from the low over central NY across southern New England, to a warm-frontal triple point southeast of Long Island, with cold front arching southward and southwestward over the northern/western Bahamas. Isolated thunder may be possible for a few more hours over portions of eastern ME, where elevated MUCAPE up to about 400 J/kg (rooted near 850 mb, atop a deep stable layer) will be possible within a precip-laden/warm-advection conveyor. Farther west, a closely aligned series of shortwave troughs was evident in moisture-channel imagery over western SK, eastern MT, and the southern WY/northwestern CO area. The middle perturbation will lose definition while the northern and southern ones dig south- southeastward, forming a large cyclone over the central/southern Rockies and adjoining High Plains by the end of the period. By then, the northern trough will close into a low over eastern MT and shift southward to eastern WY, while the southern one will develop a closed low over the TX Panhandle. Being ensconced within the broader cyclonic gyre, these two lows may begin a temporary Fujiwhara interaction late in the period, continuing on day 2. Low-level warm advection will occur over the northwestern Gulf region throughout the period, but without sufficient along- trajectory marine modification to support potentially lightning- producing convection until late tonight, after 06Z. Isolated thunderstorms may move northward across parts of the middle/upper Texas Coastal Plain thereafter. ..Edwards.. 12/01/2020
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