Flash Flood Guidance
Issued by NWS
Issued by NWS
053 AWUS01 KWNH 161925 FFGMPD MNZ000-NDZ000-170123- Mesoscale Precipitation Discussion 1023 NWS Weather Prediction Center College Park MD 324 PM EDT Mon Sep 16 2024 Areas affected...near the northern ND/MN border Concerning...Heavy rainfall...Flash flooding possible Valid 161923Z - 170123Z Summary...Showers and thunderstorms are expected to expand in coverage and shift more towards a front as an upper-level cyclone moves by the area and CIN reduces. Hourly rain totals to 2.5" with local totals to 4" are possible. Discussion...A northeast-moving upper low in western ND along with surface heating to leading to reduced CIN across portions of ND near a stationary front, which was earlier reinforced with convective outflow. Precipitable water values of 1.5" lie near the boundary. Effective bulk shear of ~40 kts exists. ML CAPE of 500-2000 J/kg exists, and is increasing. Temperatures at 700 hPa are 6-9C. The expectation is for some convective expansion with time, as ML CAPE increases beyond 2500 J/kg in the warm sector. When CIN reduces to zero, there is a question of whether the instability shifts northward to the convection or if new convection forms closer to the returning boundary. The MPD area takes both into account. Also, the degree of effective bulk shear argues for mesocyclones, which can be effective heavy rain producers. At some point, the activity will try to forward propagate, which veering 850 hPa winds strongly suggest, but the returning front should limit southward propagation, favoring a vector more to the east with time. While there is a signal for heavy rainfall in the recent mesoscale guidance, there is a bit of spread, so uncertainty is greater than normal. The ingredients suggest hourly totals to 2.5" and local totals up to 4". Since it`s falling over areas that received similar rainfall over the past 24 hours, depressing flash flood guidance values, flash flooding is considered possible, with the more significant impact in urban areas. Roth ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...BIS...FGF... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 49929486 49489441 48689448 48109673 47879792 47649882 47939969 48360027 49389767