SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1153 PM CST Tue Dec 23 2025 Valid 241200Z - 251200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS COASTAL CALIFORNIA AND THE CENTRAL VALLEY... ...SUMMARY... Thunderstorms with marginally severe wind gusts, small hail and potentially a brief tornado will be possible from Wednesday into Wednesday night along parts of the California coast, and inland across the San Joaquin Valley. ... Synopsis ... A high-amplitude midlevel pattern will persist on Wednesday, characterized by a deep trough across the eastern Pacific and a building ridge across the Plains. This pattern will maintain a broad belt of intense cyclonic flow across California into the Interior West. Throughout the day, an initial shortwave trough will continue lifting northeast from the eastern Pacific into the Pacific Northwest, while the attendant surface low lifts more northward along the coast toward Washington. Late on Wednesday a second, more potent trough will approach central and northern California -- primarily after dark. This setup will facilitate a prolonged period rain and embedded thunderstorms across California and portions of the Interior West into Thursday. ... California Coast ... Strong ascent and strengthening onshore flow will aid in modest destabilization Wednesday morning ahead of a surface cold front. An ongoing band of convection is expected across the central and southern coastal areas associated with the strongly forced ascent along the advancing cold front. Given the presence of a strong low-level jet (locally exceeding 50 knots at 1 km AGL), there is a risk that these strong winds will mix to the surface within the strongest convection resulting in damaging wind gusts. Forecast soundings across the area do maintain some low-level curvature ahead of the convective line, such that any convective element able to interact with true surface-based buoyancy would have the potential for a brief tornado. In the wake of the morning convection, a secondary surface low will intensify during the afternoon and overnight as it approaches the northern California coast. This will likely trigger another round or two of broken, low-topped convection along a second cold front. Despite weaker instability than with the morning convection, the strength of the wind fields would suggest an ongoing risk for isolated wind damage as this convection moves inland. ... Central Valley ... Cold midlevel temperatures and increasing height falls will overspread surface dewpoints in the 40s to perhaps low 50s. Although buoyancy will remain modest (MUCAPE at or below 500 J/kg), the presence of a powerful midlevel jet in excess of 100 knots will support long hodographs. This combination of modest instability and large/long hodographs may support a threat for semi-organized convection, including some potential for supercells. The strongest storms will be capable of producing damaging gusts, hail, and a brief tornado before the convection shifts east into the higher terrain and weakens. ..Marsh/Squitieri.. 12/24/2025
