SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1125 AM CST Wed Jan 27 2021 Valid 281200Z - 291200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Thunderstorms are possible across parts of coastal and interior central California, mainly Thursday night, but the risk for severe weather appears negligible. ...Synopsis... Models indicate that the amplified regime across the eastern Pacific will undergo transition during this period, with initially sharp mid/upper ridging (between 140-160 W longitude) becoming suppressed by the first in a series of digging short wave impulses. As this occurs, fairly deep, elongated downstream troughing is forecast to gradually progress inland across the Pacific coast. It appears that this will include at least one vigorous short wave impulse, which is forecast to dig into its base, accompanied by a sizable mid-level cold core with 500 mb temperatures at or below -30C. A modest surface cyclone and associated reinforcing low-level cold intrusion may also develop southward along the California coast, into areas near and southwest of Monterey by late Thursday night. Farther east, broad mid/upper ridging likely will be maintained across the Rockies into the Mississippi Valley, with perhaps some further amplification across the Great Plains. To the southeast of a blocking high near/northeast of Hudson Bay, it appears that a deep mid-level low will be forced southeastward toward the lower Great Lakes region. This will prevent eastward development of the upstream ridging, and contribute to the evolution of large-scale troughing across the Atlantic Seaboard into the western Atlantic. Strong cyclogenesis is forecast to proceed over the western Atlantic, in association with a preceding vigorous short wave impulse digging off the southern Mid Atlantic coast by the beginning of the period. In its wake, a cold front will advance southeast of the Florida Peninsula, with the leading edge of associated lower/mid tropospheric drying advancing through the Bahamas, Caribbean and southwestern Gulf of Mexico. While a southerly return flow, emanating from the southwestern Gulf of Mexico, may develop north-northwestward into the Rio Grande Valley and parts of the southern Great Plains, this will be elevated above a cool/cold, stable boundary layer. Beneath relatively warm and capping layers aloft, forecast soundings suggest that this is unlikely to yield destabilization supportive of thunderstorm activity. ...California... An initial frontal precipitation band, spreading south and east of the Monterey vicinity at 12Z Thursday, may be preceded by strong southerly flow around the 850 mb level on the order of 40-50+ kt. This may contribute to large, clockwise curved low-level hodographs across coastal areas into southern portions of the San Joaquin Valley early in the day, before the low-level jet weakens. However, forecast soundings within this regime indicate thermodynamic profiles with little potential for lightning, and lingering stable layers near the surface which is expected to preclude a severe weather risk. In the post-frontal regime, strong mid-level cooling, associated with the digging mid-level cold core, is expected to contribute to weak destabilization along and inland of the central California coast late Thursday through Thursday night. Latest forecast soundings suggest that thermodynamic profiles will probably become supportive of scattered convection, occasionally capable of producing lightning. ..Kerr.. 01/27/2021
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