SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0202 AM CDT Sat Sep 27 2025 Valid 291200Z - 301200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk for severe thunderstorms appears negligible across the U.S. Monday through Monday night. ...Discussion... Amplification within the westerlies appears likely to continue to translate eastward through this period, with mid-level ridging building across much of interior Canada and adjacent portions of the northern U.S. and downstream troughing slowly digging across the northwestern Atlantic through Canadian Maritimes and northern New England. Upstream, large-scale troughing across the mid-latitude eastern Pacific into western North America may begin to lose amplitude, as a couple of embedded short waves progress northeastward inland of coastal areas. However, it appears that deeper troughing will be reinforced offshore of the British Columbia/Pacific Northwest coast by a much more vigorous digging short wave trough, which models indicate will support renewed significant cyclogenesis across the northeastern Pacific. In the southern mid- to subtropical latitudes preceding this regime, troughing within generally weak flow is forecast to slowly shift east/northeast of the southern Rockies into the Great Plains Monday through Monday night. However, it appears that a downstream mid-level high will be maintained across the Midwest, and models indicate little general movement to weak mid-level troughing across the Southeast. A pair of tropical cyclones are likely to continue slowly migrating north-northwestward across parts of the subtropical western Atlantic, including one north of the Bahamas toward the Carolina coast. ...Carolina coastal vicinity... The timing of the approach of Potential Tropical Cyclone Nine remains uncertain, with increasing impacts along coastal areas most probable late Monday night or later. However, as it approaches coastal areas, the latest NAM output, among other guidance, suggests that cool advection aided by strengthening north to northeasterly near surface flow may contribute to a better-defined baroclinic zone near the Carolina coast, perhaps reinforced to the cool side of the boundary by evaporation of precipitation spreading downstream of the cyclone. Even if enlarged, clockwise curved low-level hodographs do evolve along coastal areas late in the period, the potential for the inland advection of a sufficiently moist and buoyant boundary layer to support a risk for tornadoes still appears negligible at this time. ..Kerr.. 09/27/2025
