SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1121 AM CST Mon Jan 25 2021 Valid 261200Z - 271200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE TUESDAY AFTERNOON OR EVENING ACROSS PARTS OF SOUTHEASTERN ALABAMA...THE WESTERN FLORIDA PANHANDLE AND SOUTHWESTERN GEORGIA... ...SUMMARY... A couple of strong thunderstorms may impact parts of the eastern Gulf Coast region late Tuesday afternoon or evening, accompanied by at least some risk for severe weather. ...Synopsis... Models indicate that there will be considerable amplification within the mid/upper flow regime across the mid-latitude Pacific through this period, including the development of sharpening ridging along an axis near 160 W longitude. To the east of this ridge axis, a vigorous digging short wave trough is forecast to contribute to deepening large-scale troughing across the eastern Pacific, and into the Pacific coast vicinity by 12Z Wednesday. It appears that this will be accompanied by a deep occluding surface cyclone, with the occluding front advancing inland across the Oregon and northern California coast late Tuesday afternoon through Tuesday night. The front may be preceded by generally modest moisture return, mostly across northern California coastal areas late Tuesday afternoon and evening, and the leading edge of the mid-level cold core associated with the short wave trough may overspread areas to the west of the Cascades late Tuesday night. However, forecast soundings remain suggestive that potential for thunderstorm activity is negligible through at least this period. Meanwhile, with the approach of the upstream perturbation, a significant short wave impulse currently digging into the Southwest is forecast to remain progressive. Models indicate that this feature will accelerate across the southern Rockies through south central portions of the Great Plains by late Tuesday night. At the same time, a downstream perturbation, becoming sheared within an increasingly confluent regime, is expected to be forced eastward/east-southeastward across southern portions of the Great Lakes region through southern New England. In response to these developments, in lower-levels, it appears that an initial surface cyclone will weaken over the upper Ohio Valley, while secondary surface cyclogenesis takes place along a warm frontal zone off the Mid Atlantic coast. As this occurs, a trailing cold front likely will advance southeast of southern Appalachians and become quasi-stationary west-southwestward across north central Gulf coastal areas by late Tuesday night. The front appears likely to stall generally near the northern periphery of subtropical ridging (centered over the Caribbean), which may maintain strength through this period, with a continuing return flow of moisture around it, along and south of the frontal zone. ...Southeast... Elevated moisture return above the frontal zone will contribute to weak destabilization and thermodynamic profiles marginally supportive of occasional weak thunderstorm activity, largely aided by forcing for ascent supported by the progressive short wave impulses. Warm mid-levels beneath the subtropical ridging, to the south of the frontal zone, seem likely to minimize thunderstorm development. However, models do suggest a window of opportunity for boundary-layer based storm development in a narrow corridor along/ahead of the surface front across parts of the western Florida Panhandle, southeastern Alabama and southwestern Georgia late Tuesday afternoon and evening. In the wake of the lead short wave impulse, and in advance of the perturbation emerging from the Southwest, models suggest that mid-levels may remain sufficiently cool, as large-scale ascent associated with low-level warm advection begins to increase, to allow for scattered thunderstorm development. In the presence of 30-50+ kt west-southwesterly flow in the 850-500 mb layer, mixed-layer CAPE on the order of 500-1000 J/kg appears possible and may contribute to strong to severe thunderstorm development capable of producing potential damaging wind gusts before diminishing Tuesday evening. ,,,Southern Rockies into adjacent portions of Great Plains... Models suggest that weak destabilization is possible across the higher terrain, and at mid-levels across adjacent portions of the high plains, beneath the mid-level cold pool associated with the impulse emerging from the Southwest. It appears that thermodynamic profiles may become at least marginally conducive to convection capable of producing lightning, but any such activity probably will be fairly sparse, with probabilities generally near the minimum threshold for a categorical thunderstorm outlook. ..Kerr.. 01/25/2021
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