Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Feb 19 2024 19:51:07 ACUS01 KWNS 191950 SWODY1 SPC AC 191949 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0149 PM CST Mon Feb 19 2024 Valid 192000Z - 201200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO EVENING ACROSS INTERIOR NORTHERN CALIFORNIA... ....SUMMARY... A couple of strong storms may impact parts of the Sacramento Valley by late this afternoon, and perhaps pose at least some risk for producing a tornado or two. ....20Z Update... There has been some adjustment to the outlook, mainly to account for the progression of the synoptic/sub-synoptic features and ongoing trends concerning instability. The occluding offshore cyclone (roughly centered near or northeast of 40N/130W at 19Z) is in the process of gradually weakening. Stronger mid-level height falls are also weakening, and spreading northeast/east of the southern Cascades and northern Sierra Nevada. However, flow appears to remain moderately strong and southerly (near or above 40 kt) around 850 mb across much of the Sacramento Valley, and this is contributing sizable clockwise-curved low-level hodographs, as insolation contributes to at least weak boundary-layer destabilization beneath modestly cold mid-level temperatures. It is not clear that forcing for ascent will support more than one or two boundary-layer based storms over the Sacramento Valley late this afternoon and evening, but the environment still appears conditionally conducive to a low-topped supercell with the potential to produce a brief tornado or two. ...Kerr.. 02/19/2024 ..PREV DISCUSSION... /ISSUED 1021 AM CST Mon Feb 19 2024/ ....Synopsis... A pronounced mid-level trough and associated surface low continue to impinge on the West Coast, supporting a continued northward transport of moisture over California into southern portions of the Pacific Northwest. 12Z observed soundings for sites along the California coast already show cooler mid-level temperatures overspreading inland, suggesting that marginal buoyancy should already be present across central into northern CA. With time, insolation will support locally higher amounts of buoyancy amid a highly sheared environment to support low-topped but organized thunderstorms capable of producing severe hazards over portions of central into northern CA this afternoon. ....Portions of central into northern CA... Low-level warm-air advection has encouraged surface temperatures to warm into the mid 50s F across southern portions of the Sacramento Valley prior to diurnal heating. By afternoon, 52-54 F surface dewpoints beneath 7.5+ C/km mid-level lapse rates will boost tall but thin SBCAPE to the 500-750 J/kg range. The BBX VAD currently depicts a sizable, curved low-level hodograph, with over 300 m2/s2 of 0-3 km SRH, and these favorable low-level shear trends are expected to persist through the day as the surface low continues to meander just offshore. Modifying RAP forecast soundings suggest that surface dewpoints need to rise at least into the 53-54F range to support efficient ingesting of SRH for tornadogenesis. It is unclear how widespread 53-54 F dewpoints will become by afternoon, with the tornado threat more conditional on these dewpoints being realized. Nonetheless, a couple of low-topped supercells are possible this afternoon, likely accompanied by at least a marginal severe hail/wind threat. $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .