Flash Flood Guidance
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Issued by NWS
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858 AWUS01 KWNH 210255 FFGMPD COZ000-NMZ000-AZZ000-UTZ000-210845- Mesoscale Precipitation Discussion 0476 NWS Weather Prediction Center College Park MD 1055 PM EDT Thu Jun 20 2024 Areas affected...Four Corners of UT, CO, NM, AZ... Concerning...Heavy rainfall...Flash flooding possible Valid 210255Z - 210845Z SUMMARY...Increased convective activity with near record low level moisture flux pose potential for efficient rainfall producing thunderstorms across complex terrain with spots of 1.5-2.5" totals resulting in possible localized scattered incidents of flash flooding. DISCUSSION...GOES-E WV suite and 00z RAOB analysis denote two subtle shortwaves moving north-northeastward along the western edge of the larger scale ridge nosing across the Southern Plains. The lead wave is crossing western CO with a favorable anticyclonic arch of cirrus with transverse banding across WY demarcating solid divergence aloft and favorable sloped ascent pattern across the central Rockies. The second wave is starting to lift north through the eastern San Francisco Plateau of northeast AZ. This shortwave is providing solid DPVA and isallobaric increased wind response of 850-500mb flow. CIRA ALPW denotes strong moisture flux into an axis of enhanced moisture across Western NM into a deeper overlapped axis from west-central AZ to the four-corners with 1.25-1" total PWat values with the axis. CIRA ALPW 850-700mb flux percentiles are at the maximum range/percentile for this time of year indicating the anomalous nature to the rainfall potential. RADAR and GOES-E EIR along with GLM lightning loops suggest a few convergence zones along and downstream of the shortwave; a SW to NE axis from N Cibola/SE McKinley to Los Alamos appears to be feeding upon best orthogonal convergence from the responding low level flow. A few cells appear to be anchored near along favored terrain delaying forward propagation and likely to result in increased rainfall totals. Given the deep moisture of .75" through rugged terrain and strong flux and axis of slowly eroding instability up to 1000 J/kg of MUCAPE should support rates of 1.0-1.25"/hr and spots of 2" are possible (perhaps higher if terrain locked). Further west into the Plateau, stronger thunderstorms appear to be aligned parallel and downstream of the DPVA lifting northeastward, suggesting short-term training/repeating could be a problem...so with similar 1"+/hr rates and 1-2 hours duration spots of 2-2.5" totals may be possible with risk area slowly drifting northeastward into CO providing some instability advection into SW CO through the overnight period. As such, scattered incidents of flash flooding are considered possible. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ABQ...FGZ...GJT...PUB... ATTN...RFC...CBRFC...WGRFC...NWC... LAT...LON 38480814 38390642 36870546 35760584 35080772 34650893 35151028 35821066 36441056 37170991 37980922