Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 03 2023 21:58:56 AWUS01 KWNH 032158 FFGMPD WYZ000-UTZ000-IDZ000-NVZ000-ORZ000-040400- Mesoscale Precipitation Discussion 1032 NWS Weather Prediction Center College Park MD 557 PM EDT Sun Sep 03 2023 Areas affected...Northern Great Basin into the Snake River Plain and western WY Concerning...Heavy rainfall...Flash flooding possible Valid 032200Z - 040400Z Summary...Showers and thunderstorms will continue to expand in coverage through this evening. These storms will at times produce rain rates of 1-2"/hr, which through training could result in axes of 2-3" of rainfall. Flash flooding is possible. Discussion...The GOES-W WV imagery this aftn clearly indicates the opening and slow eastward advection of an upper trough centered over northern NV and eastern OR. Downstream of this trough axis, mid-level divergence and broadly coupled upper jet streaks are helping to enhance deep layer synoptic ascent supporting the widespread convection. To the east, an elevated front draped SW to NE is providing a focus for additional development as southerly 850-700mb flow transports impressive moisture northward (PWs +2.5 to +3.5 sigma) and ascends isentropically atop this boundary. Additionally, subtle shortwaves embedded within the flow are helping to enhance and organize areas of convection. This pronounced ascent working into the favorable thermodynamics, especially across eastern NV where untapped instability has climbed to more than 2000 J/kg, is resulting in rainfall rates estimated by local radars as high as 1-1.5"/hr. As the upper trough continues to advect eastward this evening, the associated downstream ascent will maintain intensity while shifting gradually northeast. This acting upon the impressive thermodynamic environment should persist showers and thunderstorms well into the evening. The simulated reflectivity among the various high-res members suggests that convection will become increasingly organized during the next few hours, especially as vorticity lobes overlap the effective front, and bulk shear increases from west to east to 40-50 kts. This could result in more impressively organized clusters of thunderstorms with rain rates 1-2"/hr as reflected by HREF neighborhood probabilities, and HRRR 15-min rainfall as much as 0.5" in some cells. The mean cloud-layer winds are progged to remain quick this evening, as high as 30-40 kts to the northeast, which will be somewhat limiting to the flash flood risk. However, aligned Corfidi vectors through unidirectional low-to-mid level flow will likely result in at least short-term training, yielding HREF and RRFSE probabilities for 2" as high as 10-20%, and 20-30%, respectively. This region continues to show extremely saturated antecedent soil conditions noted by NASA SPoRT 40cm soil moisture percentiles that are generally 70-95%, suggesting rapid runoff of any of these heavy rain rates. While the soils most vulnerable to flash flooding will be in the more sensitive terrain or around recent burn scars, anywhere more significant training can occur could result in instances of flash flooding through the evening. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!67Fqun0N4q-J-QjECXMNldzWX-fwvQqL6Cop2OhEsVbdWXzLhFC-a3Cd8lUrmJJQLkih= TY55qQQcfDWkMM9ovnck7J8$ for graphic product... ATTN...WFO...BOI...LKN...PIH...REV...RIW...SLC... ATTN...RFC...CBRFC...CNRFC...MBRFC...NWRFC...NWC... LAT...LON 44371158 44371022 44130986 43500989 42431027=20 40971163 39531346 38701532 38401658 38431754=20 39081788 40481783 41721744 42521698 42571686=20 43621458=20 =3D =3D =3D 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) .