Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 01 2023 13:58:37 AWUS01 KWNH 011358 FFGMPD AZZ000-UTZ000-NVZ000-CAZ000-011800- Mesoscale Precipitation Discussion 1017 NWS Weather Prediction Center College Park MD 957 AM EDT Fri Sep 01 2023 Areas affected...Southeast CA...Southern NV... Southwest UT...Adj Northwest AZ... Concerning...Heavy rainfall...Flash flooding possible Valid 011400Z - 011800Z SUMMARY... Additional storm development on the instability and moisture gradient set up from southeast CA into southwest UT will result in continued heavy rains up to 1.5 inches per hour, which will be capable of localized flash flooding into the late morning. DISCUSSION... A weakening MCS and associated low-level circulation over northwestern Arizona is advecting anomalous moisture northward into the lower Colorado River Valley. This surge of moisture/potentially unstable air is well defined with a tight western gradient from the Peninsular Range of S CA across Riverside, central San Bernadino county into W Clark county into White Pine county, NV. This gradient also aligns with increased 850-700 deep layer confluence between southwesterly flow along and ahead of the digging larger scale synoptic trof centered near N CA and southern low-level flow out of the Gulf of California. While there is some capping near/under the weakening cirrus canopy from the dying MCS, the edge/periphery near this gradient has some higher instability values for greater convective development over the next few hours. These storms are oriented along that moisture and instability boundary and deep layer steering for the storms to be slow-moving with some possible training in proximity to urban locations near Las Vegas, NV.=20 As the morning progresses, expect continued weakening on the large scale of the rainfall shield across southern UT, but even lighter rains up to .25-.33" can remain a problem for the slot canyon regions and it is not completely out of possibility some of the storms across SE CA/S NV may track into SW UT. As the cloud shield erodes, daytime heating may allow for some increasing large-scale instability and may result in additional upstream development and is expected to change though this afternoon, but placement remains quite uncertain given the cloud cover and an update additional MPD may be required. In the near term, flash flooding is most likely over the next few hours in urban areas particularly around the Las Vegas metro as well into the slot canyons of southern/southwest UT, and is considered possible.=20 Wegman/Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9ZdypnoDxoESTAxTV-t_d7EElEJg_oUpniqR8DHWC6EtQ0ZIiQn1WNxuHOErIRyWr-lT= oviILLYhTjpB8ZlLbf-BuLc$ for graphic product... ATTN...WFO...FGZ...SLC...VEF... ATTN...RFC...CBRFC...CNRFC...NWC... LAT...LON 38821171 37261139 36411263 35591457 34761634=20 35841687 37851486 38701358=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) .