Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue May 30 2023 18:01:44 AWUS01 KWNH 301801 FFGMPD MTZ000-UTZ000-IDZ000-NVZ000-CAZ000-ORZ000-310000- Mesoscale Precipitation Discussion 0386 NWS Weather Prediction Center College Park MD 201 PM EDT Tue May 30 2023 Areas affected...Northern Sierra Nevada through the Northern Great Basin Concerning...Heavy rainfall...Flash flooding possible Valid 301800Z - 310000Z SUMMARY...Scattered areas of slow-moving showers and thunderstorms are expected to develop this afternoon which will be capable of producing rainfall rates of over 1 inch/hour. Isolated instances of flash flooding will be possible. DISCUSSION...The latest GOES-W visible satellite imagery is showing the development and expansion of a CU field across areas of the northern Sierra Nevada and extending northeast across much of the northern Great Basin which will soon lead to the onset of convective initiation across these areas. Strong diurnal heating is already fostering SBCAPE values of as much as 1500 J/kg with the greatest instability pooled up across areas of northern NV and into southern ID. Meanwhile, the airmass across the region is anomalously moist with PWs well over the 90th percentile of climatology as seen in the 12Z RAOB data from REV, LKN and BOI. The CIRA-ALPW data also shows moisture that is rather concentrated in the 700/500 mb layer. Thus, the thermodynamic environment will be conducive this afternoon for convection that will be capable of producing heavy rainfall rates. The main forcing mechanisms for convection include a pair of slow-moving MCVs, with one over northeast CA and another one along the OR/NV border. This energy should drift gradually off to the northeast this afternoon, but will be combine with local orographics and a few differential heating boundaries for convection to initiate and expand in coverage. More broadly there is also a weak lingering mid-level shear axis across the region which may foster at least some weak deeper layer ascent. Despite an environment conducive for just pulse cell convection, the weak steering currents over the region will yield slow cell-motions. The 12Z HREF guidance does support these cells producing rainfall rates of as much as 1 to 1.5 inches/hour, with some localized storm total amounts of 2 to 3 inches by late afternoon. Some of the area streams are running above normal, and these additional amounts today will be capable of producing isolated instances of flash flooding. Any burn scar locations will tend to be the most susceptible to runoff concerns, and especially with the high rainfall rate potential. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5sYHpVI8IDWUhJhE1HSDngdj5qShRMktBBGsT8nypE7FsAPhKcmniA53RUxHgApR2YUX= ClpxUfZa1CBo1QX6IjQfvZ8$ for graphic product... ATTN...WFO...BOI...EKA...LKN...MFR...MSO...PDT...PIH...REV... SLC...STO...TFX... ATTN...RFC...CBRFC...CNRFC...MBRFC...NWRFC...NWC... LAT...LON 45201592 45141395 44811289 44121195 43181136=20 42301182 41491464 41231701 40871834 39961945=20 39221970 39022015 39552066 40102098 40612130=20 41042195 40312294 40652311 41212318 41582267=20 42152131 42902009 43761894 44731748=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) .