Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 23 2024 19:48:34 ACUS01 KWNS 231948 SWODY1 SPC AC 231946 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0246 PM CDT Fri Aug 23 2024 Valid 232000Z - 241200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF WESTERN MONTANA... ....SUMMARY... Strong to severe storms with severe wind gusts and some hail are possible across Montana, the Intermountain West and central Rockies, southeast Arizona to extreme southwestern New Mexico, and parts of the High Plains. ....20z Update... The primary adjustment for this update was an expansion of the Slight risk/15% wind probability southward to include more of western MT. Slowly intensifying convection across eastern ID is expected to remain relatively benign for the near-term (see MCD #1976 for additional details regarding short-term trends), but may pose a more robust severe wind threat later this afternoon/evening as convection spreads north into a deeply mixed environment across western MT. The last several HRRR solutions have captured recent convective and environmental trends well and consistently suggest the best potential for severe wind will be associated with this activity as it spreads north. The adjustment to the Slight risk area should better reflect this potential. Elsewhere, the forecast remains on track per the previous discussion (below). See MCD #1977 for the latest details regarding the severe threat across southern Arizona. ...Moore.. 08/23/2024 ..PREV DISCUSSION... /ISSUED 1127 AM CDT Fri Aug 23 2024/ ....Intermountain West to northern Rockies... The lead portion of an upper trough centered along the coastal Pacific Northwest will shift north-northeastward over the northern Intermountain region in tandem with the exit region of a strengthening mid/upper-level jet. Scattered thunderstorms are expected in this regime preceding the Pacific Coast trough, with initial development over the higher terrain ahead of the surface cold front. Isolated severe gusts and marginally severe hail will be possible, with the potential for a more focused corridor of stronger wind gusts across northwest/north-central Montana late this afternoon through early evening. Additional thunderstorms should form this afternoon across east/northeast Oregon, northern/eastern Idaho, to western Wyoming, and southeastward into Utah/western Colorado, as eastern fringes of large-scale ascent preceding the Pacific Northwest trough and embedded shortwaves overlie destabilizing, elevated terrain. Throughout the corridor, sufficient deep-layer shear (30-45 kt) should exist for organized multicells and small bowing/outflow-driven clusters, and perhaps a few supercells, with some hail and severe-caliber wind gusts possible. ....High Plains... Isolated to widely scattered thunderstorms are expected to form over the central/northern Rockies, as well as near the lee trough over eastern Montana this afternoon, with another favored corridor across the central High Plains including northeast Colorado/western Nebraska. Activity should move east-northeastward across the adjoining High Plains. This convection will encounter a diurnally destabilizing, well-mixed boundary layer with steep low-level lapse rates, supporting isolated severe wind gusts. Isolated large hail also will be possible. Strongly difluent mid/upper-level flow will exist over most of this corridor, between the Pacific Northwest cyclone and the southern Plains anticyclone, with speeds generally increasing northwestward and low-level moisture greater southward across the central High Plains. Still, sufficient moisture should persist near the Montana lee trough, along with enough veering with height over the entire area to yield enough deep shear (30+ kt effective-shear magnitudes) for organized convection. ....Southeast Arizona/far southwest New Mexico... Widely scattered to scattered thunderstorms are expected to develop this afternoon with a relatively moist air mass and ample insolation. Increasing mid-level southerlies around the western rim of the anticyclone should enable 20-30 kt effective-shear magnitudes, and enough northward storm motion to augment already strong downbursts from the most intense cells locally. An instance or two of marginally severe hail could also occur. $$ = = = 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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .