Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Aug 21 2024 05:54:20 ACUS01 KWNS 210554 SWODY1 SPC AC 210552 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1252 AM CDT Wed Aug 21 2024 Valid 211200Z - 221200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF EASTERN MONTANA AND WESTERN NORTH DAKOTA.... ....SUMMARY... Scattered thunderstorms, some with severe hail and damaging gusts, are expected to develop today over parts of far eastern Montana and western North Dakota. ....Synopsis... A mid-level shortwave trough over north-central California early this morning will move across the Great Basin and emerge across eastern Montana this afternoon. This shortwave trough will be the focus for a severe weather threat this afternoon/evening across eastern Montana and western North Dakota. Farther east, a mid-level trough centered over the Plains will start to break down during the day today. As this occurs, surface troughing is forecast to develop from the northern Plains to the central High Plains. Scattered strong to potentially severe storms are expected along the extent of this surface trough from western South Dakota to eastern Colorado. ....Eastern Montana and western North Dakota... Significant heating is forecast across eastern Montana this afternoon with temperatures forecast to warm into the mid to upper 90s (depending on the degree of mixing). This will result in moderate instability and a mostly uncapped atmosphere by mid to late afternoon. DCVA ahead of the approaching mid-level trough will result in sufficient deep-layer ascent for thunderstorm development by mid to late afternoon. These storms will likely be supercellular in nature as mid-level flow strengthens to near 50 knots while the associated mid-level jet streak overspreads the region. The long-straight hodograph may also support some splitting storms. Large hail (up to golf ball size) and severe wind gusts of 60 to 80 mph will be the primary threats associated with this activity. ....Western South Dakota to eastern Colorado... Scattered thunderstorm activity is expected within a broad surface trough from western South Dakota to eastern Colorado where moderate to strong instability will be in place by mid-afternoon. Mid-level flow will be mostly weak across this region (15 to 20 knots) which will limit the overall shear magnitude. However, moderate southeasterly flow ahead of this surface trough, coupled with the westerly mid-level flow may result in adequate shear for storm organization and perhaps a few slow-moving supercells. The deeply mixed boundary layer across this zone will support a threat for severe wind gusts with isolated hail as a lesser threat (predominantly associated with any more robust supercell development which may occur). A few regions within the marginal risk may have a greater threat (southwest South Dakota/northern Nebraska and northeast Colorado), but it is not clear at this time whether coverage/intensity will be sufficient for a slight risk. ....Southeast Arizona... A surge of monsoon moisture across southern Arizona will result in moderate (1500-2000 J/kg MLCAPE) instability and scattered to widespread thunderstorm development this afternoon. Storm organization will likely be somewhat weak given the weak shear (~15 knots). However, the moderate instability in a deeply mixed boundary layer will support an isolated severe-wind threat. In addition, the widespread nature of the convection will likely result in numerous outflow boundary collisions which may locally enhance updraft intensity and support a few stronger cells. ...Bentley.. 08/21/2024 $$ = = = 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) .