Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 09 2023 16:55:49 AWUS01 KWNH 091655 FFGMPD MTZ000-092300- Mesoscale Precipitation Discussion 0449 NWS Weather Prediction Center College Park MD 1255 PM EDT Fri Jun 09 2023 Areas affected...Southern & Central MT Concerning...Heavy rainfall...Flash flooding likely Valid 091700Z - 092300Z SUMMARY...Widespread thunderstorms this afternoon may produce rainfall rates >1.5"/hr in areas with overly saturated soils. Flash flooding is likely to occur in parts of southern and central MT this afternoon. DISCUSSION...The jet stream pattern remains mired in upper troughing over the Great Basin and a strong ridge over the Canadian Prairies. Low pressure over the Intermountain West and building high pressure in south-central Canada is responsible for a prolonged stretch of southerly low-mid level moisture advection into the northern Rockies and High Plains. 12Z upper air soundings show an abundance of atmospheric moisture present, while NAEFS at 18Z features PWs at or above the 99th climatological percentile in east-central MT. There are also breaks in the cloud cover over southeast MT, northern MT, and northern WY, helping to increase instability parameters over the next few hours. Storms will form initially along a surface trough draped over southern MT, but their is also a cold front approaching from the north that will help out in producing strong thunderstorms later this afternoon. The environment is likely to contain 500-1,000 J/kg of MLCAPE and PWs between 1.0-1.3". HRRR area averaged soundings around 19Z in southeast MT show an atmospheric column featuring RH low-mid level values of 80-85%, dew points near 60, and mean cloud layer less <10 knots. Warm cloud layer depths are also on the order of 8,000-9,000' deep, which combined with the >80% RH present support efficient warm rain processes. Plus, LCL-EL cloud layer wind speeds are less than 10 knots and in some cases could be closer to 5 knots. The latest 12Z HREF shows a notable 50-80% probability area for 6-hr QPF > 10-yr ARI in central and eastern MT, which are higher than HREF guidance depicted for yesterday's stormy setup. The anomalous moisture content, supportive instability, and slow storm motions alone support rainfall rates not just >1"/hr, but could approach 2"/hr in the most intense cells. These would support a flash flood threat not even taking into account antecedent soil moisture conditions. That being said, soils remain exceptionally saturated and sensitive in central MT where the past 14-days worth of rainfall have ranged between 4-8" above normal in some areas according to AHPS. Soils are not as sensitive in southeast MT, but the atmospheric parameters mentioned would still produce hourly rainfall rates that could surpass 1-3hr FFGs. Flash flooding is likely in parts of Big Sky country this afternoon, especially in areas where soils are most sensitive and in poor drainage areas. Mullinax ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-G5nqzhfgXjI9l6Rw716lrm9dU6urjdLXBuzJo7mfmmaLMrinQ0Mpyt2x0wPrxb9T_C3= IOrwtHAWUnUo78nECaxSAB4$ for graphic product... ATTN...WFO...BYZ...GGW...TFX... ATTN...RFC...MBRFC...NWC... LAT...LON 48891055 48780808 47710565 46650426 45830415=20 45160464 45320615 45790789 46180953 46751068=20 47761109=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) .