Flash Flood Guidance
Issued by NWS
Issued by NWS
448 AWUS01 KWNH 090007 FFGMPD KSZ000-COZ000-090600- Mesoscale Precipitation Discussion 0410 NWS Weather Prediction Center College Park MD 806 PM EDT Sat Jun 08 2024 Areas affected...far Eastern Colorado, much of Kansas Concerning...Heavy rainfall...Flash flooding possible Valid 090004Z - 090600Z Summary...Widespread thunderstorms in eastern Colorado will likely merge into an MCS this evening and move west to east across Kansas. Rainfall rates of 2-3"/hr are likely, which could produce 2-4" of rain with locally higher amounts. Flash flooding is possible. Discussion...The regional radar mosaic this afternoon shows widespread thunderstorms moving across eastern Colorado with embedded supercells containing radar-estimated rain rates of 1.5 to 2 inches per hour. These thunderstorms are expanding in a region of ascent forced via easterly upslope flow and through low-level convergence along a stationary front. A convectively enhanced shortwave racing through the flow from the west is also contributing ascent to the area. This resulting impressive lift is occurring into robust thermodynamics to support heavy rainfall, with PWs reaching 1.3 to 1.5 inches, overlapping a ribbon of MLCAPE of 2000-3000 J/kg. The greatest instability and moisture is currently pooled over central/eastern KS, but persistent E/SE flow between 925-850mb will draw these more elevated thermodynamics to the west to support intensification and expansion of thunderstorms as they emerge from CO. As convection pushes east this evening, it will encounter bulk shear above 50 kts, supporting MCS development as storms move across Kansas. There is good model and ingredient support for this evolution, so confidence is high in this progression, and rainfall rates within this MCS will likely (40-60% chance) exceed 2"/hr, with short term rates of 3+"/hr possible. This MCS may become forward propagating as it tracks to the east, so rainfall duration may be somewhat muted. However, downstream of this MCS an increasing LLJ reaching 25-30 kts from the S/SW will efficiently merge into a convergence axis along the nose draped west to east across KS. With this LLJ resupplying ample moisture and instability into the region, additional thunderstorm development along this axis and ahead of the MCS is likely as shown by most available high res CAMs. Thunderstorms that develop along the LLJ will feature repeating rounds, and with rain rates here also likely reaching 1-2"/hr, where this convection overlaps with the MCS sweeping through later in the evening, some areas may receive 2-4" of rain with locally higher amounts. Parts of KS have received more than 200% of rainfall the past 7 days according to AHPS, and although the coverage is variable, this has reduced FFG to below 2"/3hrs in many areas. The HREF 3-hr FFG exceedance probabilities peak above 40%, highest across areas that get both LLJ thunderstorms and the MCS, but 0-10cm RSM from NASA SPoRT is only 25-35%. This could limit the FF risk at least somewhat, so it appears instances are possible, but additional MPDs may be needed to address a greater FF risk later tonight. Weiss ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...DDC...GID...GLD...ICT...PUB...TOP... ATTN...RFC...ABRFC...MBRFC...NWC... LAT...LON 39670153 39300028 38919855 38799696 38359569 38049549 37789553 37559560 37299599 37179681 37109824 37080013 37230163 37720245 38960311 39660264