Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Aug 26 2025 22:01:25 AWUS01 KWNH 262201 FFGMPD NVZ000-CAZ000-ORZ000-270300- Mesoscale Precipitation Discussion 1012 NWS Weather Prediction Center College Park MD 600 PM EDT Tue Aug 26 2025 Areas affected...Northern Sierra Nevada Range & Far Northern California... Concerning...Heavy rainfall...Flash flooding possible Valid 262200Z - 270300Z SUMMARY...Strong convective thunderstorms capable of 1.5"/hr with potential for training across complex terrain of the Northern Sierra Nevada Range may result in localized flash flooding concerns through the late evening. DISCUSSION...GOES-W Visible and 10.3um trends show strong, cooling thunderstorms continue to expand and merge into a larger somewhat linear feature. RADAR and lightning animation, denote cells are strengthening/expanding but also propagating outward both west and east off the main ridge lines across northeast CA into far western NV. Total PWat analysis shows northern Central Valley and Great Basin are well above normal (at 1.2" ranges) with nearly localized maximum values over the last 30 years; while elevated, the northern Sierra Nevada range has similar, if slightly lower percentiles due to the lack of overall vertical depth to reach values near .7-.9" required. Still, the available moisture is highly anomalous to support highly efficient rainfall production given local surface Tds in the low 50s and with temperatures into the mid-70s, suggest CAPE values are slightly higher than analyzed at 1000-1500 J/kg. This supports rates of 1.5"/hr given weak but moist upslope convergent flow. Along the northwest periphery of the larger scale wave in the Great Basin has resulted in deeper layer steering/confluence across the northern Sierra to support a southwestward cell motions, this may allow for short-term training/repeating over the next few hours as the remaining inability is exhausted and cells further expand outward/downslope in each perpendicular to the mean flow. As such a spot or two of 2" totals remains possible in 30 to 90 minutes, given complex terrain and low FFG values (1-1.5" in 1 to 3hrs), localized flash flooding may be possible through the next few hours before instability/heating is fully exhausted. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-nr_auTAfUNqfK8xidrMCzmQkP4k__XItyVXXqq2AuFJ93DicLLDeIMBRiqJC2Mi5viQ= hia5OeDFB7a81VILZlhpcs0$ for graphic product... ATTN...WFO...MFR...REV...STO... ATTN...RFC...RSA...NWC... LAT...LON 42032213 41802136 41352043 40932002 40501969=20 40111941 39261907 38801945 38781994 39332050=20 39972096 41032182 41432229 41682250 41962248=20 =20=20=20=20=20=20=20=20=20=20=20=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .