Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Aug 07 2023 20:30:09 AWUS01 KWNH 072030 FFGMPD MTZ000-IDZ000-ORZ000-WAZ000-080200- Mesoscale Precipitation Discussion 0883 NWS Weather Prediction Center College Park MD 429 PM EDT Mon Aug 07 2023 Areas affected...Southeast WA...Northeast OR...Central ID...West to Southwest MT... Concerning...Heavy rainfall...Flash flooding possible Valid 072030Z - 080200Z SUMMARY...Slow Moving/Merging cells along deformation zone pose localized 1-2" totals through evening. Widely Scattered to Scattered instances of flash flooding are possible, particularly over steeper terrain. DISCUSSION...GOES-W WV suite depicts a drying arc along the upwind edge of the mid-level trof axis with nose of the 70-80kt 300mb jet streak having recently rounded the base into SE OR and the Western ID Snake River Plain. Older shortwave center over central WA is transferring energy to the shortwave at the cyclonic rotor of the aforementioned jet. This is providing very strong left exit and anticyclonic diffluence aloft across SE WA into central ID to provide solid broad scale ascent. Full insolation across much of the area has allowed for solid instability to build across this area, though dense cirrus within the jet has enhanced a differential heating boundary bisecting OR from W to East and across the Snake River Plain of W ID, the deeper return moisture through the Columbian Plateau could not filter eastward to enhance deeper layer moisture though 700mb RH remains above 70% and CIRA LPW shows older lingering moisture axsi across the region with .25-.4 through much of the area in both the 850-700 and 700-500 layer (only exception was a bit of low level drying in the SE Sawtooth and SW MT ranges, but with surface Tds of upper 40s to lower 50s, there should be ample moisture for above average rainfall rates. The key will be moisture advection, and as the older 700mb low in WA weakens, and transfers southeast across NE OR into ID, flow should accelerate toward 15-20kts at cloud base increasing convergence expanding convective coverage across the shear axis between the circulations and across the older weak 700mb low in west-central MT. This should delay cell motions with potential for outflows to collide after first/second up/downdraft cycles. As such, rain rates up to 1"/hr are possible and with mergers/collisions some spots of 1-2" totals are possible across the area of concern, particularly where divergence/outflow aloft can maintain updraft a bit longer than typical pulse convection.=20 Combined with recent spotty heavy rainfall over the past few days, similar widely scattered to scattered instances of flash flooding are considered possible through late evening with timing from west to east timed with best DPVA/left exit to nose of 3H jet streak. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_FVYWk4uo3i_otX-J6Srk6H4PByZXTvqKtLy3DIcZ8t9M38S2H8eJwCWQ29UYKb26hDJ= brDa189PqV6lYhJRy0XIOMI$ for graphic product... ATTN...WFO...BOI...MSO...OTX...PDT...PIH...TFX... ATTN...RFC...MBRFC...NWRFC...NWC... LAT...LON 48671667 48421608 48021560 47251420 46841277=20 46591150 45961118 44821124 44041179 43661416=20 43461592 43461774 43851908 44721888 45441812=20 45731824 46681848 47181919 47751932 48401835=20 48661758=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) .