Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Sep 03 2024 05:35:29 ACUS01 KWNS 030535 SWODY1 SPC AC 030533 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1233 AM CDT Tue Sep 03 2024 Valid 031200Z - 041200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO THIS EVENING ACROSS PARTS OF CENTRAL IDAHO...MUCH OF SOUTHERN MONTANA...WYOMING...MUCH OF NORTHERN UTAH AND ADJACENT NORTHWESTERN COLORADO...INTO PARTS OF THE WESTERN DAKOTAS... ....SUMMARY... Thunderstorms developing across the northern Rockies and adjacent portions of the Great Basin by this afternoon may produce scattered strong to locally severe wind gusts, before spreading eastward toward the northern Great Plains into this evening. ....Synopsis... Downstream of split mid/upper flow across the eastern Pacific, Alaska and Canadian Yukon vicinity, the stronger westerlies remain confined to the higher latitudes, with weaker zonal flow prevailing across the northern tier of the U.S., on the northern periphery of weak/suppressed subtropical ridging. Seasonably moist boundary-layer air has generally become confined to the southern tier of the U.S., to the south of notable surface ridging. Little change appears likely through this period, though the center of the ridge may shift from the lower Great Lakes/upper Ohio Valley into the northern Mid Atlantic. It does appear that the westerlies may undergo some amplification across the northeastern Pacific into Canada later today through tonight, including building mid-level ridging offshore of the Pacific Northwest and British Columbia coast and digging mid-level troughing to the lee of the Canadian Rockies. As this occurs, a remnant mid-level trough over the interior northwestern U.S. is forecast to slowly shift into and across the northern Rockies. ....Northern Intermountain Region and Rockies... Models indicate that the mid-level trough will weaken while shifting eastward today, but it still appears that mid-level forcing for ascent and cooling will remain sufficient to support continuing convective development, including considerable thunderstorm activity this afternoon and evening across the higher terrain. Near the mid-level cold core, destabilization, including mixed-layer CAPE on the order of 500-1000 J/kg, might support a few thunderstorms capable of producing marginally severe hail across the mountains of southwestern Montana. Otherwise, more modest CAPE, based above a warm and deeply mixed boundary layer, may still become supportive of locally strong to severe downburst winds across the higher terrain of western Wyoming and northern Utah, into the Great Salt Lake Desert. Eastward into the northern high plains, severe weather potential, and the extent to which destabilization is able to maintain thunderstorm development, remains more uncertain. However, some model output, perhaps most notably the past few runs of the NAM, has been suggestive that convective development near/north of the Absaroka Range and Big Horn Basin vicinity may generate sufficient consolidating outflow to support a substantive east-southeastward propagating surface cold pool to the lee of the higher terrain. Although 03/00Z NAM forecast soundings, for example, are not particularly indicative that vigorous thunderstorm development will be maintained, they suggest that 35-50 kt winds may accompany a surging gust front, in this run across southeastern Montana and adjacent northeastern Wyoming by late evening and into western South Dakota overnight. ...Kerr/Moore.. 09/03/2024 $$ = = = 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) .