Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Aug 03 2023 22:05:12 AWUS01 KWNH 032205 FFGMPD KSZ000-NEZ000-SDZ000-COZ000-WYZ000-040300- Mesoscale Precipitation Discussion 0850 NWS Weather Prediction Center College Park MD 604 PM EDT Thu Aug 03 2023 Areas affected...Eastern WY...Southwest SD...Western NEB...Northeast CO... Concerning...Heavy rainfall...Flash flooding possible Valid 032200Z - 040300Z SUMMARY...Increasing coverage and rainfall intensity expected across the High Plains. Sub-hourly to hourly totals of 1-2" crossing saturated soil conditions may induced scattered flash flooding instances through early overnight period. DISCUSSION...Height-falls are starting to spread eastward into the High Plains as the core of the mid-level large scale trof presses eastward out of Western WY. Persistent low level upslope flow has been fluxing increasing moisture through the Central High Plains with surface Tds into the upper 50s near the terrain increasing to the mid-60s by 102W, while CIRA LPW depicts 850-500mb values of .4 to .5" though both main layers, resulting in a north-south fairly tight gradient of 1 to 1.5" total PWats across the area of concern from west to east. Southwesterly flow out of the terrain in association with the height-falls has strengthened overall convergence to spark scattered thunderstorms along the length of the height-falls from an effective mid-level triple point vorticity center in SE MT, along E WY into NE CO, it is here across central CO that mid-level drier air is washing over helping to steeping mid to upper level lapse rates (and likely decreasing rainfall efficiency). As such, flux convergence within modestly buoyant environment with 1000-2000 J/kg of CAPE will support stronger updrafts with sufficient moisture loading to support intense rainfall rates (along with hail generation). Given deeper southwesterly flow aloft in combination with easterly inflow, forward propagation is likely to be quick supporting cell motions over 15-30kts; slower to the north in WY to SD and quicker to the south across CO into KS. HRRR and 12z ARW seem to be handling the evolution best within the Hi-Res CAM suite, but still suggest sub-hourly totals of 1-1.5" and spots of 1.5-2.5" through the early overnight period, increasing with time further east into the deeper moisture environment. This alone would not likely induce all but the most prone areas to flood; however, recent (7-14 day) well above normal rainfall per AHPS are 300-500% of normal with exception over the Black Hills and spots around and south of the Lake-Palmer Divide. As such, this has likely reduced capacity for efficient infiltration, especially at the rates expected, resulting in spots of possible flash flooding through the evening. This could be more likely further north, across NE WY/SD, where a band of thunderstorms has developed along some effective low to mid-level convergence axis or effective WAA boundary...though also aligns with that area NOT receiving heavy rainfall over the last week or two. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4Ci3IO8bK3r6VpzA1EchOT-xCgrlLuslWdKdJEZ0V_a1d0V8I8ZqVZ1wCu-pm-H3U5SE= RXr3AKI-Fe3YQExhkBrRnRQ$ for graphic product... ATTN...WFO...BOU...CYS...GLD...LBF...UNR... ATTN...RFC...ABRFC...MBRFC...NWC... LAT...LON 44960491 44910389 44730281 44260159 43430107=20 42890165 42640226 42140249 41570216 41040189=20 40430185 40000181 39400181 39010246 38960320=20 39080372 39330470 39850484 40630486 41980490=20 43120520 44170584 44800583 44900550=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) .