SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0155 PM CST Fri Jan 29 2021 Valid 292000Z - 301200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Weak thunderstorm development remains possible across parts of the Southwest into Great Basin late this afternoon and evening, with weak thunderstorms also possible across parts of the south central Great Plains overnight. ...20Z Outlook Update... Some adjustments to the categorical (10 percent probability) thunderstorm line have been made to account for the progression of the synoptic features, and latest trends concerning ongoing destabilization. Large-scale mid-level troughing, including a significant smaller-scale impulse just now in the process of advancing inland of the southern California coast, may be accelerating east-northeastward a bit farther north than generally indicated by prior model output. Beneath a lead smaller-scale impulse, weak boundary-layer destabilization is occurring, northward across portions of southern/eastern Nevada. This is contributing to deepening convective development, in an environment where thermodynamic profiles may become marginally conducive to lightning for a few hours late this afternoon. Otherwise, as the more significant trailing impulse progresses inland, it appears that the onset of mid-level warming may contribute to diminishing risk for thunderstorms near southern California coastal areas as early as 22-23Z. The extent of the risk for thunderstorms eastward across the lower Colorado Valley into Arizona is becoming more unclear due to at least some offset of the diurnal heating cycle with the arrival of the stronger mid-level cooling/forcing for ascent. However, at least isolated thunderstorm development still appears possible by this evening. Farther east, precipitation associated with moistening and large-scale ascent above an elevated mixed-layer, is stabilizing mid-level lapse rates across parts of the Texas South Plains/Panhandle vicinity. However, the onset of mid-level cooling and strengthening lower/mid tropospheric forcing for ascent may contribute to weak thunderstorm development toward the 03-06Z time frame, before spreading northeastward overnight. ..Kerr.. 01/29/2021 .PREV DISCUSSION... /ISSUED 1030 AM CST Fri Jan 29 2021/ ...Southern California into Arizona... Upper trough moving into southern CA this morning will continue into AZ this evening. Ascent and steep mid-level lapse rates accompanying the primary vorticity maximum are spreading into southern CA, where isolated thunderstorms should persist this afternoon. The risk for a few thunderstorms will spread into AZ as lapse rates steepen by late afternoon into the evening. ...Southern Plains region... Steep lapse rates (7.5-8 C/km) in the 700-500 mb layer are in place across the Southern Plains. Though low-level moisture is limited, a plume of mid-upper level subtropical moisture is spreading northeast ahead of the southwestern U.S. upper trough. A few lightning flashes remain possible today with shallow mid-level convection developing in this plume. The primary corridor of thunderstorm development is expected late tonight from the Texas Panhandle and northwest Texas through western and central OK. Deeper forcing for ascent within a strengthening warm advection regime and approach of the shortwave trough will promote destabilization in the 700-300 mb layer, and scattered thunderstorms will likely develop, primarily after 08Z.
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