Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 02 2023 17:13:28 AWUS01 KWNH 021713 FFGMPD AZZ000-UTZ000-NVZ000-CAZ000-022300- Mesoscale Precipitation Discussion 1025 NWS Weather Prediction Center College Park MD 113 PM EDT Sat Sep 02 2023 Areas affected...Southern NV...Southeast CA...Northwest AZ...Southwest UT... Concerning...Heavy rainfall...Flash flooding likely Valid 021715Z - 022300Z SUMMARY...Thunderstorm activity will increase over next few hours. Intense, efficient rainfall production with possible sub-hourly totals up to 1.25" with limited infiltration suggest widely scattered instances of flash flooding. Favorable flow environment may even allow for a few repeating cells/streets with localized totals up to 2".=20 DISCUSSION...While main surge of anomalous moisture/flux shifted through the region yesterday, there still remains a favorable thermodynamic airmass in place with continued high Theta-E air reinforcing through the Lower Colorado Valley into S NV. The region remains along the eastern periphery/influence of larger scale synoptic trof over California as seen in GOES-W WV suite.=20 It is those height-falls/pressure anomalies drawing low level return flow westward more than normal in monsoonal flow, with surface Tds into the mid to upper 50s as far west as BIH to NW of TPH to W of EKO, supporting a tight moisture gradient. Combined with enhanced 700mb flow and fairly unidirectional steering flow. While this mid-level flow weakens a bit further east. The WV suite also depicts a compact and potent shortwave is lifting out of eastern Pacific crossing SW AZ. This will provide DPVA for increased vertical ascent over the next few hours as the surface starts to heat under fairly unobscured skies (numerous cu streets and eroding valley stratus. Given Tds into the 70s across the Lower Colorado, total moisture values of 1.5+ are accessible to favorable development areas (ridge lines, etc) ahead of the shortwave. Even with limited SBCAPE, a few cells have already developed in E Mojave county lifting north. Still, overall coverage and vertical development is expected over the next few hours peaking toward the 20-21z time frame, given CAPEs likely reaching toward 1500-2000 J/kg. In a fairly deep layer south-southwesterly to southwesterly flow, convergence is likely going to be limited and multiple narrower streets of thunderstorms are likely to be the mode for development, still the amount of moisture and storm scale flux should support very intense rates with 1-1.25" falling in sub-hourly (15-30min) time frames.=20 Orientation of the streets may allow for some repeating tracks, especially with upstream redevelopment probable along favored terrain and continuously strong 850-700mb upstream flow. As such, spots of 2" are possible, only compounding high runoff, given limited infiltration in desert/rock soil types. The potential for training should be greater further west and along the western edge of the lifting shortwave near the aforementioned dewpoint/moisture gradient and stronger 700mb flow. While incidents of flash flooding are likely to be smaller in coverage and perhaps lower in magnitude that prior days, it is considered likely through 22z. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!50tvpqN8akzDCShpux6OQez_gbe-JZ1BCn-0nAkcWgToqBxEnVhoav4pPAg8AjCMjV7u= TzAPaEGEghLNo_QUjpGVuPQ$ for graphic product... ATTN...WFO...FGZ...LKN...SLC...VEF... ATTN...RFC...CBRFC...CNRFC...NWC... LAT...LON 39401216 38941110 37331112 35861130 34811147=20 34251184 34391293 34461421 34471536 34671621=20 35221700 36441725 37991670 39111601 39281511=20 39161424 38401406 38301319=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) .