Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Aug 26 2025 20:17:25 AWUS01 KWNH 262017 FFGMPD MTZ000-IDZ000-ORZ000-270200- Mesoscale Precipitation Discussion 1010 NWS Weather Prediction Center College Park MD 416 PM EDT Tue Aug 26 2025 Areas affected...Central Idaho (Salmon River Range) Concerning...Heavy rainfall...Flash flooding possible Valid 262015Z - 270200Z SUMMARY...Increasing slow moving thunderstorms capable of 1"+/hr rates will eventually expand into a favorable collision/merger environment and support 1-2"+ totals resulting in scattered localized incidents of possible flash flooding. DISCUSSION...GOES WV suite depicts solid SE to NW short-wave ridging axis across central ID with very favorable divergence aloft as the northwestern edge of the jet streak expands westward across MT, further tightening the ridge axis as the core of the trough slides northeast into NE NV, south-central ID later tonight. While in the lowest levels, southerly moisture influx continues to filter through the Snake River Plain up into the terrain. RAP analysis suggests 850-700mb convergence axis is approaching, all the while, filtered sunlight has been increasing surface temperatures and with the increased moisture, greater instability. Currently MLCAPEs have reached 500 J/kg with limited capping; and a few of the highest peaks have seen convective development. As greater moisture and peak heating (1000 J/kg) increase toward 21-22z, expect convective vigor and coverage to expand throughout the range. At the apex of the ridge, mean steering flow will remain weak and persistent/increasing southerly upslope flow may allow for increased duration/redevelopment through the peaks before moving off. HRRR and WoFS rapid refresh suggest increasing coverage and slow motions with 15 and 5 minute rates suggestive of .5" and .2" rates, respectively, resulting in 1" exceedance probabilities to near 70-90% toward 23-00z. This is likely, as initial thunderstorms develop outflows, this will broaden moisture convergence for increased convective coverage and border updrafts with each up/down cycle. Mean cell motions of 5-10kts toward the north and northeast, countered by propagation toward the south due to inflow, suggests likelihood of cell mergers and localized instances of effectively stationary motions will allow for localized totals of 1-2". Naturally low FFG (.75-1"/hr & 1-1.5"/3hrs) may be exceeded; while soils are dry per NASA SPoRT LIS generally below 25% compared to average, the harder top layers may be a bit more hydrophobic initially and if rates are intense enough should limit inflation and further increase run-off and potential for localized flash flooding. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!74pzFHqSJ8_XIdH-Y1UL7U9_mRLu7r4pLrEUZ-SpWKC10pCONMWsddZTtjyctxdMo63a= UGrO5MZgF2ZubsoZG5zGCSU$ for graphic product... ATTN...WFO...BOI...MSO...PIH... ATTN...RFC...PTR...NWC... LAT...LON 45661480 45531416 44711333 44051275 43521308=20 43381397 43461543 43811675 44731706 45431601=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) .