Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Aug 07 2023 14:42:03 AWUS01 KWNH 071441 FFGMPD IDZ000-ORZ000-WAZ000-072040- Mesoscale Precipitation Discussion 0880 NWS Weather Prediction Center College Park MD 1040 AM EDT Mon Aug 07 2023 Areas affected...Portions of the Pacific Northwest Concerning...Heavy rainfall...Flash flooding possible Valid 071440Z - 072040Z SUMMARY...Scattered slow-moving clusters of heavy showers and thunderstorms may produce instances of flash flooding going through the early afternoon hours. DISCUSSION...The latest GOES-W IR satellite imagery shows a mid to upper-level low gradually digging across the Pacific Northwest which will be interacting with an anomalously moist and increasingly unstable airmass going through the day. The latest satellite trends are showing a gradual expansion of slow-moving shower and thunderstorm activity with locally cooling convective tops across areas of northeast OR through central to northeast WA. Over the next several hours heading into the afternoon, a combination of relatively steep mid-level lapse rates and diurnal heating should lead to a more pronounced destabilization of the column and should support an increase in the coverage of shower and thunderstorm activity. Increasingly divergent flow aloft ahead of the height falls will further drive ascent that will be conducive for seeing at least scattered clusters of slow-moving convection given the rather weak steering flow. Some of the greater concentration of convection heading into the afternoon hours may tend to be over southeast WA and into northeast OR near the ID border where eventually stronger instability and relatively focused low to mid-level convergence is expected to set up. The 06Z HREF guidance supports locally heavy rainfall totals over these areas and some elevated probabilities of seeing the 100-year ARI exceeded for a 6-hour period. PWs across the region are rather moist and running as high as 2 to 3 standard deviations above normal, and this coupled with the increasing instability profiles with time should favor convective cells with increasingly heavy rainfall rates. The 06Z HREF guidance shows rather high probabilities (>50%) of seeing 1+ inch/hour rainfall rates with the evolving convective cells going into the afternoon hours, and some of the strongest cells may produce 1.5 to 2 inches in an hour given the anomalous moisture pooled over the region. Some storm total amounts may locally reach 2 to 4 inches through early afternoon, and this may produce instances of flash flooding. The more sensitive burn scar areas, and urbanized locations, will be most susceptible today to runoff problems and concerns for flash flooding. Will continue to closely monitor. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5gzggI9KXVm4jMduq-fqGJLmBn664tU2e2xWrTTlheFsaFCoSjYrhzQXZTQTZzhfV7yL= KIfOgX15TO215ouoAWO3Ets$ for graphic product... ATTN...WFO...BOI...MSO...OTX...PDT... ATTN...RFC...NWRFC...NWC... LAT...LON 49051912 49011742 47841607 46101521 44821603=20 44521754 44721883 45401968 46572010 47312046=20 48052050 48682002=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) .