Area Forecast Discussion
Issued by NWS Topeka, KS
Issued by NWS Topeka, KS
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419 FXUS63 KTOP 211925 AFDTOP Area Forecast Discussion National Weather Service Topeka KS 225 PM CDT Sat Sep 21 2024 .KEY MESSAGES... - Widespread rain and T-storms tonight with some severe risk this evening and heavy rains overnight. - Much cooler weather arrives on Sunday and lasts into next week. && .DISCUSSION... Issued at 157 PM CDT Sat Sep 21 2024 A large scale upper low was located across northeast AZ this afternoon while another upper wave was located across the ND/MN region. The northern stream upper wave has pushed a cold front into northwest KS this afternoon. At 19Z the sfc map showed low pressure around CNK with a sfc trough extending southwest toward Medicine Lodge and the cold front approaching Hays. Dewpoints were in the upper 60s to around 70 in the warm sector while PWATs were approaching 2" which would be near record values for the date across northeast KS. Latest mesoanalysis shows MLCAPE of 1500-2500j/kg with around 100 CINH remaining along with effective shear of 25-35kts. Forcing ahead of the upper system is already supporting t-storm development across the OK Panhandle and that area of lift/convection is expected to move ENE toward the area later this afternoon/evening. Another area to watch is along the actual front across north central KS into southern NE where additional storms should develop later this afternoon into this evening. This area of storms could impact parts of the area as well with some risk for hail/wind at least for several hours this evening. The overall scenario should see increasing storm development from the southwest ahead of the upper low in the mixed unstable but perhaps still capped atmosphere from the southwest along with additional storm development along the front this evening. Both areas of convection should eventually yield a larger area of rain and t-storms as the upper low approaches and the LLJ increases this evening. Heavy rains will occur and areas of 1-2" should be common tonight with some receiving 2-3" or more depending on how the convective area evolves especially this evening through midnight. Cannot rule out some flash flood risk in urban areas if training sets up however given how exceptionally dry it has been the creek/river flood risk remains low. After midnight the models suggest that the LLJ/winds in the 925-850 mb layer should veer and focus the better low level convergence to our east and MUCAPE values are forecast to drop to below 1000j/kg. This should result in more rain and embedded thunder after midnight into Sunday morning as the upper low gradually emerges and weakens. Expect a much cooler Sunday with remnant showers and the cooler weather will stick around into at least early next week with below avg highs in the 60s and 70s expected. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1144 AM CDT Sat Sep 21 2024 VFR conditions will persist until after 00Z when thunderstorms will develop along a cold front mainly to the northwest of the TAF sites and move across the area through 6Z. Exact coverage and location of the storms remains somewhat in question so have inserted VCTS in that time frame. As the night wears on rainfall coverage should increase with occasional rain and sct tsra expected overnight through at least 12z. As winds shift to the north and the cold front passes expect CIGS to drop into the IFR category toward 12z Sunday. && .TOP WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Omitt AVIATION...Omitt