Subj : DAY1SVR: Day 1 Convective To : All From : Mike Powell Date : Mon Feb 19 2024 08:33:00 ACUS01 KWNS 191249 SWODY1 SPC AC 191248 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0648 AM CST Mon Feb 19 2024 Valid 191300Z - 201200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF INLAND NORTHERN CALIFORNIA.... ....SUMMARY... A tornado or two may occur in the Sacramento Valley region of California today. ....Synopsis... The large-scale pattern will continue to be characterized by a longwave trough just off the West Coast, ridging over the Rockies and High Plains, and a trough over parts of the eastern CONUS and eastern Gulf. Progressive, well-developed shortwave troughs -- now apparent in moisture-channel imagery over GA and the central High Plains -- will move through the broader-scale cyclonic-flow field of the eastern longwave trough. Conditions should remain too stable in low levels to support a thunder threat over land from the Intermountain West eastward to the Atlantic Coast. Upstream, a large cyclone off northern CA and the Pacific Northwest will weaken gradually and shift northward through the period, devolving into an open wave synoptic trough. However, the broader- scale troughing will be maintained, as a strong shortwave perturbation now in the cyclone's northwestern quadrant digs southward then southeastward, approaching 130W west of southern CA and northern Baja by 12Z. These processes will maintain a fetch of southwest flow aloft across CA. A weaker shortwave trough is moving inland over north-central CA, and should cross northwestern NV today before reaching parts of ID around 00Z. ....CA... Scattered showers and isolated to widely scattered thunderstorms are expected this afternoon into early evening. Isolated supercells are possible, with a threat for a tornado or two. Mostly subsevere hail and convective winds are expected, through the largest hail and gusts may briefly reach severe limits. As noted above, the initial shortwave trough is crossing the area, preceded by a precip plume with isolated embedded thunderstorms over the central/northern Sierra and San Joaquin Valley. In the weak subsidence following that perturbation, a few hours of relatively tranquil conditions are expected. Thereafter, upper-level forcing will be nearly neutral, but with diurnal/diabatic heating contributing to low-level destabilization over the Sacramento Valley/Delta region and perhaps northernmost parts of the San Joaquin Valley, beneath favorable low/middle-level lapse rates and weakening of MLCINH. Episodic, isolated to scattered convection and a few thunderstorms are possible again this afternoon into evening, in an environment characterized by favorably veering/increasing winds with height. Orographically forced backing of surface flow in the valley likely will be slightly greater than most models indicate as well, further enlarging already favorable hodographs progged for supercells. Any quasi-linear modes also may contain LEWP/bow features with embedded mesocirculations. Effective SRH of 150-300 J/kg and 40-55-kt effective-shear magnitudes are possible. With surface dewpoints holding generally in the low/mid 50s F, the preconvective/inflow sector may attain 250-700 J/kg peak MLCAPE, based on modifications to the 12Z OAK RAOB and model soundings. A combination of nocturnal surface cooling/stabilization and outflow air should reduce severe potential after dark. Isolated storm-scale rotation also is possible with cells mainly over the Pacific marine layer off the northwestern CA coastline, with waterspout/tornado potential nonzero but too low/conditional over land for an outlook area at this time. ...Edwards/Mosier.. 02/19/2024 $$ --- SBBSecho 3.14-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/105) .