SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1118 AM CST Sun Dec 28 2025 Valid 291200Z - 301200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Aside from parts of the lower Rio Grande Valley, the risk for thunderstorms appears negligible across much of the U.S. Monday through Monday night. ...Discussion... Within one branch of westerlies emanating from the northern mid-latitude Pacific, models indicate that broad mid-level ridging will be maintained across British Columbia and the Pacific Northwest through the Canadian/northern U.S. Rockies and adjacent Prairies/Great Plains through this period. Downstream troughing may undergo further amplification as a surface cold intrusion progresses south/southeastward through the Gulf Basin. However, the primary embedded short wave perturbation is forecast to rapidly pivot east and northeast of the lower Great Lakes and Ohio Valley toward the Canadian Maritimes and northwestern Atlantic Monday through Monday night. While the center of an associated broad, slowly deepening and occluding surface cyclone shifts east-northeast of Lake Huron/Georgian Bay through southern Quebec, it appears a secondary surface low may develop across northern New England into the lower St. Lawrence Valley. In its wake, the trailing cold front is forecast to rapidly advance east/southeast of the Appalachians, and well offshore of much of the Atlantic Seaboard by 12Z Tuesday. ....Lower Great Lakes into New England... NAM and Rapid Refresh forecast soundings indicate that lower/mid-tropospheric warming and moistening, preceding the secondary surface frontal wave development, will contribute to weak elevated destabilization across portions of eastern New York state through New England during the day Monday. This may contribute to deeper convective development embedded within an evolving broader precipitation shield. The extent to which this could become capable of producing lightning remains a bit unclear, but probabilities for weak thunderstorms still seem best characterized as less than 10 percent. ...Lower Rio Grande Valley... NAM and Rapid Refresh forecast soundings, and other model output, suggest that widely scattered weak thunderstorm activity is possible along or just behind the cold front as it advances across Deep South Texas late tonight. Timing of the frontal passage and associated convection through the lower Rio Grande around Brownsville remains uncertain, but low thunderstorm probabilities may linger an hour or two beyond 12Z Monday. ..Kerr.. 12/28/2025
