Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Aug 22 2024 23:55:28 AWUS01 KWNH 222355 FFGMPD KSZ000-NEZ000-COZ000-230530- Mesoscale Precipitation Discussion 0922 NWS Weather Prediction Center College Park MD 754 PM EDT Thu Aug 22 2024 Areas affected...High Plains of Colorado, Kansas, and Nebraska Concerning...Heavy rainfall...Flash flooding possible Valid 222353Z - 230530Z Summary...Showers and thunderstorms will expand and organize into clusters as they move into the High Plains this evening. Rainfall rates of 2"/hr or more are likely in deeper convection, resulting in axes of 2-3" of rain with locally higher amounts possible. This could result in instances of flash flooding. Discussion...The regional radar mosaic this evening depicts increasing convective coverage which has blossomed over the higher terrain and is beginning to emerge into the lower elevations of the High Plains. This activity is developing in response to a modest shortwave lifting northeast around the periphery of a mid-level ridge of high pressure, which is interacting with a stationary front over northeast CO to produce ascent. The thermodynamic environment is becoming increasingly favorable for heavy rainfall, with PWs measured by GPS of 1-1.2 inches streaming northwestward from the Central Plains and identified in LPW products, combined with MLCAPE of 1000-2000 J/kg along a sharp E-W gradient from CO into KS. This is already supporting rainfall rates estimated by KFTG WSR-88D of 1-1.5"/hr in fast moving convection. As the evening progresses, the high-res CAMs are in good agreement that thunderstorms will expand and grow upscale into clusters or potentially an MCS. This will occur in response to increased 0-6km bulk shear reaching 30-40 kts in tandem with the amplification of the LLJ towards 40 kts arcing NW into the KS/CO border. This LLJ will resupply favorable MUCAPE northward into the stationary front, providing plentiful thermodynamics for continued convection well into the early nighttime hours. Additionally, as the LLJ surges, a sharp theta-e gradient will develop where moisture transport vectors converge, providing additional focus for heavy rain development. The HREF neighborhood probabilities suggest thunderstorms will have at least a 20% chance of containing 2"/hr rainfall rates, with short duration rates of 3-4"/hr possible in the most organized convection as reflected by HRRR 15-min rainfall accumulations. Despite the general fast motion of cells as progged by 850-300mb mean winds of 15-25 kts, short term training along the front or the moisture gradient is possible, resulting in 2-3" of rain with locally higher amounts potentially approaching 5" (10-15% chance according to the HREF). Portions of NE Colorado and SW Nebraska been quite wet the past 7 days as noted via AHPS rainfall departures that are 300% of normal, causing compromised 3-hr FFG as low as 1.5". Although storms should be generally fast moving, the intense rain rates and any short term training could exceed this FFG leading to rapid runoff. This could cause instances of flash flooding through early tonight. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9wbuZx_IzaiLWp6vb5PMvluuoKv6d72j7nd75vTN0d52P3O22stY2qM1f5pwyBwZQXmA= _PQAV3wylwn6D73wPsiQU9g$ for graphic product... ATTN...WFO...BOU...CYS...DDC...GLD...LBF...PUB... ATTN...RFC...ABRFC...MBRFC...NWC... LAT...LON 41830172 41210131 40570084 39820038 39240017=20 38710038 38130103 37830174 37870228 38270273=20 38860317 39810393 41370371 41710263=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .