Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 23 2023 18:32:28 AWUS01 KWNH 231832 FFGMPD MTZ000-WYZ000-232330- Mesoscale Precipitation Discussion 0571 NWS Weather Prediction Center College Park MD 231 PM EDT Fri Jun 23 2023 Areas affected...northern Wyoming, southern Montana Concerning...Heavy rainfall...Flash flooding possible Valid 231830Z - 232330Z Summary...Showers and thunderstorms will gradually expand in coverage through this aftn with rain rates increasing to 1"/hr or more. Some training of these rain rates could produce 2-3" of rain possibly resulting in instances of flash flooding. Discussion...The GOES-W WV satellite imagery this aftn indicates an intensifying closed mid-level low centered over northwest UT with shortwaves rotating cyclonically to the north. These shortwaves are driving locally enhanced ascent to produce intensifying showers and thunderstorms, with a WPC analyzed surface boundary helping to organize this convection. Downstream of this upper low, 500mb winds via the SPC RAP analysis indicate increasing divergence, driving impressive deep layer ascent into WY and MT. This intense ascent is impinging into an area of favorable thermodynamics characterized by GPS measured PWs of 0.6 to 0.8 inches, around the 90th percentile according to the SPC sounding climatology, and SBCAPE of 1500-2000 J/kg. This is supporting radar-estimated rain rates of around 1"/hr from KRIW WSR-88D. As the upper low continues to deepen and shift slowly northeast, forcing for ascent should improve and become intense from northern WY into eastern ID and much of MT. Shortwaves rotating around this feature will drive periods of locally enhanced ascent to organize waves of convection, and as PWs increase to above 1" on easterly 850mb 20kt winds, the intensity and coverage of thunderstorms is likely to rapidly increase. This is modeled well by the simulated reflectivity in much of the available high-res guidance, which is reflected by HREF probabilities reaching 70% for 1"/hr rates (20% for 2"/hr), and HRRR 15-min rainfall reaching above 0.75 inches. Although storm motions should remain progressive to the north on 20kt 0-6km mean winds, aligned Corfidi vectors indicates the potential for training or repeating rounds of heavy rainfall which could result in more than 3 inches of rain in some areas. Adding to the flash flood risk this aftn is saturated antecedent soils from 14-day rainfall that is widely above 300% of normal leading to USGS streamflow anomalies that are around the 90th percentile and FFG as low as 0.75"3/hrs. These antecedent conditions suggest any heavy rain could quickly become runoff resulting in instances of flash flooding, especially within any more sensitive terrain features. This event is just beginning this aftn, and it is likely that future MPDs will be needed for portions of this same area as the flash flood threat increases tonight. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-Sj3e8mUMOZVlMl2zeTppSGO_dx5ZYzmc84-C576P_sF9C5fuBePnXCpR9ivVbLSpHbt= _1m5Jke5ZXKaH0FRfdtJ1Ys$ for graphic product... ATTN...WFO...BYZ...RIW...TFX...UNR... ATTN...RFC...MBRFC...NWRFC...NWC... LAT...LON 46350768 46060624 45760548 45260471 44820470=20 44610519 44320580 44010677 43600791 43310850=20 43440922 43800953 44270996 44361021 44501069=20 44711105 45001123 45351113 45771045 45941013=20 46310909=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) .