Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jun 05 2023 12:52:05 ACUS01 KWNS 051252 SWODY1 SPC AC 051250 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0750 AM CDT Mon Jun 05 2023 Valid 051300Z - 061200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE SOUTHERN APPALACHIANS...SOUTH TEXAS...WESTERN MONTANA...AND PARTS OF EASTERN AND NORTHERN CALIFORNIA... ....SUMMARY... Isolated strong to severe thunderstorms may occur today across portions of the southern Appalachians, south Texas, western Montana, and parts of eastern and northern California. Both occasional damaging winds and hail appear possible. ....Synopsis... On synoptic and larger scales, a blocky mid/upper-level pattern will continue through the period, surrounding a broad anticyclone now centered over southern MB. This feature will remain strong and quasistationary, but may shrink some on the north side, in response to shortwave activity over western and eastern Canada. A 500-mb trough will persist from a small cyclone now over ID southeastward through a Colorado col, and into an area of cyclonic flow containing several vorticity maxima across central/south TX and the western/central Gulf. A well-defined cyclone initially over the Atlantic -- east of Cape Cod and south of ME -- will pivot slowly northeastward toward the southern coast of NS through the period. A synoptic trough will extend from that cyclone's center southwestward across the Carolinas and diffusely connecting to the other trough over the Gulf. The eastern portion of a weak shortwave trough -- evident in moisture-channel imagery over the Lower Great Lakes -- will dig southeastward in backside cyclonic flow, reaching the NC/VA border region and lower/middle Ohio Valley by 00Z, before splitting and weakening. Meanwhile, west of the messy omega block, The ID cyclone will devolve to a shortwave trough today and move northward to the northern Rockies. A broad, cut-off cyclone initially centered near 33N124W -- or about 275 nm west-southwest of LAX -- will pivot east-northeastward today, reaching the coast around the VBG/Point Conception area by about 06Z. This feature should move little thereafter, through at least a large part of day 2. At the surface, two Atlantic cold fronts were drawn at 11Z that become slow-moving to quasistationary inland: 1. From the northern low across northeastern NC, then across southwestern VA and southern KY, and 2. From well east-northeast of DAB across north-central FL and near the Gulf coast of AL/MS to the middle TX Coastal Plain and LRD area. Otherwise, the pattern east of the Rockies remains rather muddled, with subtle boundaries, outflow remnants, and generally weak winds. Though very isolated damaging gusts or marginal hail cannot be ruled out of a large swath of the southeastern and south-central CONUS, the best-organized areas of marginal severe potential appear to be over south TX and parts of the southern Appalachians region. ....South TX... Isolated to scattered thunderstorms are possible all afternoon and into evening, mainly along and south of the remnant front/outflow boundary, with locally strong-severe gusts/hail possible. Composited radar imagery indicates an MCV roughly between CLL-VCT, which should move slowly southeastward to Gulf coastal waters today. With the EML and related capping being quite weak over this area, sustained heating should allow convective temperature to be reached by midday to early afternoon, with residual boundaries helping to focus lift near the broader-scale mid/upper trough. Mid-60 to near 70 F surface dewpoints and strong heating should contribute to peak/preconvective MLCAPE in the 2000-3000 J/kg range, amid modest lower-tropospheric flow and a somewhat enhanced channel of midtropospheric northwesterlies southwest of the MCV, and upper/anvil-level flow around 50-60 kt. This will support areas of 35-45-kt effective-shear magnitudes, in support of some storm organization. ....Southern Appalachians/Piedmont and vicinity... Widely scattered to scattered thunderstorms should develop over higher terrain this afternoon near and south of the front and move southeastward into a deeper, diurnally mixed/destabilized boundary layer. Isolated damaging to marginally severe gusts and large hail are possible. Although poleward of the southern front, residual moisture will be sufficient to support development amid sustained insolation of elevated terrain, and related weak capping. Forecast soundings show MLCAPE in the 1000-2000 J/kg range, atop steep low-level lapse rates, with weak winds/shear in the boundary layer. However, being on the southwestern rim of 30-40-kt midtropospheric northwesterlies associated with the Atlantic cyclone, 35-45-kt effective-shear magnitudes will support a blend of organized multicells and transient supercell modes. Activity should weaken substantially after sunset as the boundary layer stabilizes. Deep shear, large-scale support, and overall convective coverage each should generally lessen with westward and southward extent across the South from this outlook area. However, brief/isolated afternoon pulse gusts/hail near severe limits will be possible between here and the TX outlook area. ....Western MT... The approach of the remnant 500-mb low/shortwave trough will spread large-scale lift over the region, overlying diurnal heating of a marginally but sufficiently moist boundary layer to support scattered thunderstorm development. Weak MLCINH and lower-elevation surface dewpoints generally in the mid 40s to lower 50s F, along with steep low-level lapse rates and deepening/mixing of the boundary layer -- will support MLCAPE ranging from around 300-800 J/kg in the mountains to near 1000 J/kg around the northern I-15 corridor. Weak low-level flow/shear is forecast, beneath nearly unidirectional deep-layer winds, elongating low/middle-level hodographs. The best-organized cells could offer isolated severe gusts and/or marginal hail. ....Eastern/northern CA... Widely scattered thunderstorms are possible this afternoon, developing over higher terrain of the Sierras and moving northwestward, with the potential for isolated severe hail/gusts. Favorable moisture is apparent over the region, with surface dewpoints expected to remain mostly in the 50s (near 50 F at lower elevations, even through the diurnal heating/mixing period. The latter process will remove MLCINH preferentially early over the higher terrain, but with very steep low/middle-level lapse rates forecast, keep enough moisture to support pockets of 500-1000 J/kg MLCAPE near the outlook axis. Veering and strengthening of flow with height is expected in the form of a dominant low-level easterly flow component (locally modified orographically), surmounted by mid/upper-level southeasterlies around the northeast rim of the Pacific cyclone. While effective-shear magnitudes still will be modest (up to about 35 kt), a few organized cells may produce strong-severe gusts or hail. ...Edwards/Smith.. 06/05/2023 $$ = = = 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) .