Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon May 01 2023 12:30:43 ACUS01 KWNS 011230 SWODY1 SPC AC 011229 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0729 AM CDT Mon May 01 2023 Valid 011300Z - 021200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF NORTHWESTERN NEVADA AND EASTERN OREGON... ....SUMMARY... Isolated severe thunderstorm gusts may affect parts of a corridor from northwestern Nevada to eastern Oregon, late this afternoon into evening. ....Synopsis... A highly amplified pattern has developed in mid/upper levels, with mean troughs over the eastern CONUS and near the West Coast, and an effectively transcontinental ridge from central MX across the U.S. Rockies to the western Arctic Coast of Canada and beyond. The large cyclone drifting eastward over the Great Lakes, and associated surface frontal passages, will keep the air mass too dry and/or stable for thunderstorms over most of the CONUS east of the Rockies, except for a regime of cold-core lapse-rate steepening aloft and residual low-level moisture in northern parts of the Northeast. The West Coast mean trough is anchored by an elongated cyclone, whose center was evident in moisture-channel imagery over the Pacific, about 125 nm west of UIL. The 500-mb low will move southward to south-southeastward through the period, reaching a position offshore, but near the latitude of the CA/OR border by 00Z, then near SFO by 12Z tomorrow. As that occurs, a strong, basal shortwave trough -- now located from coastal northwestern CA southward over the Pacific -- will pivot inland over central/ southern CA around 00Z, then eject northward and weaken considerably by 12Z. As this occurs, a gradual process of low-level cyclogenesis is forecast near the southern OR/ID border, with slow-moving cold front arching central NV to southeastern CA. ....NV-OR... Widely scattered thunderstorms may develop by mid/late afternoon over northwestern NV near the front, where both frontal and heating-related lift are influential. Activity then should move north-northwestward to northwestward, close to the orientation of the cyclonically curving mean-wind vectors, while offering strong to locally severe gusts. A deep, well-mixed layer should develop in the lower-elevation portions of the warm sector, beneath enough low-level moisture/theta-e to support 100-500 J/kg MLCAPE. Intense mid/upper-level southeasterlies will contribute to favorable deep shear, especially near and north of the surface low where low-level flow is most backed, hodographs elongate considerably, and 50-60-kt effective-shear magnitudes may be realized. The convection is expected to become elevated (inflow rooted above surface) as it encounters decreasing instability with northwestward extent across eastern/northern OR this evening, from both diabatic surface cooling and lower ambient theta-e. However, isolated/ conditional potential for downdrafts to punch strong-severe gusts through a shallow, cooling layer may persist in time somewhat beyond the loss of SBCAPE, as long as activity remains organized in favorable elevated instability. ...Edwards/Mosier.. 05/01/2023 $$ = = = 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) .