SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1055 PM CST Tue Jan 12 2021 Valid 131200Z - 141200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Showers, occasionally accompanied by lightning, are possible in a corridor across the eastern Gulf Coast states into the Carolinas today through tonight. ...Synopsis... Strong cyclogenesis appears underway across the mid-latitude Pacific (near/west of 160 W longitude), with substantial further development forecast. Through 12Z Thursday, the center of the evolving broad, deep and occluding cyclone is forecast to slowly migrate across the northeastern Pacific, toward the Gulf of Alaska. Coinciding with this development, considerable amplification of downstream mid/upper flow appears likely, with pronounced ridging developing along an axis from the subtropical eastern Pacific northward through Canadian Pacific coastal areas. To the east of the mid-level ridging, models indicate that a vigorous short wave trough will dig across and to the lee of the northern Rockies. It appears that this will be accompanied by deepening surface troughing across the eastern Great Plains into upper Mississippi Valley, to the south of a deep surface cyclone migrating across the Canadian Prairies. This likely will extend as far south as the southern Great Plains, but lingering surface ridging across the northwestern Gulf of Mexico will preclude a return flow of Gulf moisture. Seasonably moist boundary-layer air will remain confined to the south of a quasi-stationary frontal zone, generally south of the Florida Peninsula and Keys into the southern Gulf of Mexico. In response to the upstream developments, a short wave trough and embedded mid-level low, emerging from the southern Great Plains, are forecast to accelerate east-northeast of the lower Mississippi Valley today, across and east of the south Atlantic Seaboard. It appears that this will contribute to a developing frontal wave off the Carolina coast, and potential for vigorous thunderstorm development along a trailing cold front. This could initiate close to southeastern Florida coastal areas, but offshore. Much of the nation will remain generally stable with negligible risk for thunderstorms. However, there does appear at least low probabilities for convection capable of producing lightning in a narrow corridor across the eastern Gulf Coast states into the Carolinas. ...Southeast... Although well to the cool side of the surface frontal zone, 13/00Z soundings do indicate the presence of relatively steep mid-level lapse rates across much of the region, in advance of the mid-level low emerging from the southern Great Plains. With the approach of the low, forecast soundings indicate elevated moisture return near the base of this layer (around the 700 mb level) will contribute to weak CAPE supportive of convective development. Aided by forcing for ascent in the exit region of an associated mid-level jet, which may continue to slowly strengthen as it propagates eastward through the period, it appears that thermodynamic profiles may become at least occasionally supportive of lightning with some of this activity. This is expected to remain confined to a narrow corridor near the 700 mb thermal gradient, across parts of the eastern Gulf Coast states into the Carolinas by tonight. ..Kerr.. 01/13/2021
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