Flash Flood Guidance
Issued by NWS
Issued by NWS
581 AWUS01 KWNH 072309 FFGMPD MOZ000-IAZ000-KSZ000-NEZ000-080500- Mesoscale Precipitation Discussion 0405 NWS Weather Prediction Center College Park MD 708 PM EDT Fri Jun 07 2024 Areas affected...South-Central Nebraska through northeast Kansas Concerning...Heavy rainfall...Flash flooding possible Valid 072308Z - 080500Z Summary...Thunderstorms, including supercells, are expected to increase in coverage and coalesce into an MCS into this evening. Rainfall rates of 2-3"/hr will accompany the strongest convection, which could result in 2-4" of rainfall with locally higher amounts. Flash flooding is possible. Discussion...The GOES-E IR satellite imagery this evening is showing clusters of rapidly cooling cloud tops to nearly -70C associated with supercells moving across central NE. This convection is blossoming in response to ascent produced via a shortwave rotating E/SE through the mid-level flow impinging upon low-level convergence along a stationary front analyzed by WPC. South of this boundary, the environment is extremely favorable for heavy-rain producing thunderstorms characterized by a plume of PWs around 1.7 inches over KS, near the daily record according to the SPC sounding climatology, overlapping MLCAPE of 1500-2500 J/kg. There is also pronounced bulk shear noted via the SPC RAP of 50-65 kts, which has supported supercells near the Sand Hills of NE, within which MRMS rainfall has been measured at 2.5-3" within 1 hour. As the evening progresses, it is likely these cells over NE, as well as some developing in northern KS, will continue to expand southeast and merge into a more broad cluster or MCS. This is supported by a pronounced instability gradient aligned NW to SE which should support the southeast motion of thunderstorms, which will be enhanced by an increasingly robust LLJ out of the S/SW. The intensifying LLJ will not only tighten the instability gradient, but should also resupply moisture downstream of expanding convection, with SREF 850-700mb moisture flux progged to exceed 2.5 sigma this evening as the LLJ peaks around 40 kts. The high-res CAMs are struggling to match the current radar initialization, but despite that, they are all in agreement that thunderstorms should expand and congeal within the robust thermodynamics and impressive bulk shear. Rainfall rates within thunderstorms could exceed 3"/hr at times as reflected by the 15-min HRRR precip accumulation fields, and 20-25% chance of 2"/hr rates noted in the HREF. Although elevated mean winds and some forward propagation may limit the duration of these rates, short term training is possible embedded within the clusters, and the HREF neighborhood probabilities indicate a 20-30% chance of at least 3", and 10-15% for 5", focused near the KS/NE border. 0-10cm RSM from NASA SPoRT is modest across NE/KS, but is locally higher due to 7-day rainfall of 100-150% in southeast NE and northeast KS. This is where the FFG is relatively compromised, and HREF exceedance probabilities for 3-hr FFG is as high as 20-30%. This further reflects the increasing risk for isolated to scattered flash flooding through this evening. Weiss ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...DDC...EAX...GID...GLD...ICT...LBF...OAX...TOP... ATTN...RFC...ABRFC...MBRFC...NWC... LAT...LON 41920045 41819886 41529733 40839543 39799473 38609519 38349694 38469812 38979930 39950004 41050069