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Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
303 FOUS30 KWBC 020101 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 901 PM EDT Mon Jul 1 2024 Day 1 Valid 01Z Tue Jul 02 2024 - 12Z Tue Jul 02 2024 ...A MODERATE RISK OF EXCESSIVE RAINFALL IS IN EFFECT FOR PORTIONS OF EASTERN NEBRASKA TO SOUTHWESTERN IOWA... ...Central/Northern Plains to Upper Midwest... Convection has been growing upscale and will continue to do so into the evening across the northern half of the Plains. The most concerning area for flash flooding will be across parts of Nebraska to Iowa, where the nocturnal LLJ of 50 knots will be maximized in a moist environment fed by both Gulf moisture and Pacific moisture rounding the mid-upper ridge, near a warm front. HRRR runs are explicitly showing 1.5-2"/hour rates, which would exceed the FFG, and other (albeit older) CAMs show higher total QPF. HREF probabilities for exceeding 3 and 6 hr FFG are greater than 50 percent in some areas. Since the 18Z HREF is getting to be older available model data at this point, focused the upgraded/embedded Moderate Risk a bit on the southern side, where recent HRRR runs are focusing the best potential for some training/backbuilding. Refer to MPD 537 for more information on this area. Additional convection farther north through the night could cause additional flash flooding risks and the Slight Risk is maintained there in parts of the Dakotas to Minnesota. ...Southeast... A cold front slowly working its way south near the South Carolina/Georgia coast is pooling moisture along it for some ongoing convection. The risk level overall has dropped since this afternoon, prompting removal of the Moderate Risk but maintained a Slight for slow-moving storms. The Savannah, Georgia area is likely the most vulnerable to additional localized flooding concerns. ...Southwest... Monsoonal moisture with PWs over the 95th percentile/2-3 standard deviations above normal in the Four Corners states is causing ongoing convection that has prompted several Flash Flood Warnings. Storms will persist further into the evening and a Marginal Risk remains in place. Tate Day 2 Valid 12Z Tue Jul 02 2024 - 12Z Wed Jul 03 2024 ...A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE UPPER MIDWEST TO CENTRAL GREAT PLAINS... 20z Update: Still on track for a heavy rainfall event over portions of MO, IA, WI and IL Tuesday afternoon into the overnight hours. Plenty of synoptic forcing with a mid level trough and right entrance of an upper jet moving across the region. Organized convective development is likely, and with PWs over 2", heavy rainfall rates are expected. There does appear to be some training/backbuilding potential, with low level flow parallel and nearly equal to the deep layer flow resulting in weak Corfidi Vectors. Do anticipate some cold pool forward propagation off to the southeast with time, which may end up limiting the duration of heaviest rain. Although that cold pool could run out of momentum somewhere over northern MO, which may enhance the flash flood risk. We did give some consideration to a MDT risk upgrade, but opted to remain at a higher end Slight risk. Uncertainty on the extent of convective training, model spread, and the fact that this region is not as saturated as areas further north...all led to maintaining the high end Slight and not upgrading at this time. We will continue to monitor high res model trends. Chenard ...Previous Discussion... ...Upper Midwest through Central Great Plains... A reinforcing shortwave trough rounding the upper trough that will be over the Dakotas Tuesday morning crosses the Neb/SD border through the day. Right entrance jet streak dynamics warrants maintenance of ongoing activity over the central Plains, IA, and central WI that then drifts south/southeast through the day that spreads No big changes were made with this update. Concerns remain from the KC metro and northeast over an expansive area to western IL and up through much of WI as gulf-sourced moisture (PWs 2 to 2.5 sigma above normal) with deep layer SW flow allowing training thunderstorm concerns. A Moderate Risk may be needed somewhere between KC and Madison WI, but for now consider this a higher end Slight Risk. ...Southeast... A Marginal Risk is maintained over the Florida Panhandle and southern GA. This will be a continuation of the convection from Monday night ahead of a slow moving cold front. Rainfall still expected to be lower than on Monday, but the plentiful Gulf moisture allows for the potential for very high rainfall rates. ...Southwest... Again maintained a Marginal over eastern AZ/western NM with a suppressed Monsoonal flow day as troughing to the north shunts the ridge axis farther east to the lower Miss Valley. Elevated moisture is limited to the southern portions of those states and remnant stratus from Monday night activity may further suppress Tuesday activity. Jackson Day 3 Valid 12Z Wed Jul 03 2024 - 12Z Thu Jul 04 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE CENTRAL PLAINS AND MID-MISSISSIPPI VALLEY... 20z Update: Only minor changes made with this update. Still on track for a heavy rainfall threat over portions of eastern KS into much of MO and into southern IL. A stalling front and PWs over 2" should set the stage for potential flash flood issues. Forcing is a bit weaker to start the period, which raises some questions to the coverage and organization of convection. By Wednesday night we should see better forcing approach from the west and a potential uptick in low level moisture transport into the boundary. The ingredients appear to be in place for upscale convective growth Wednesday night over this corridor with some training potential. Thus this is a solid higher end Slight risk with at least isolated to scattered flash flooding appearing probable. However still some questions as to the coverage and magnitude of this event, and current model QPFs are not really supportive of any higher risk at this time. So will maintain a Slight and continue to monitor. Chenard ...Previous Discussion... ...Midwest to Great Plains... A cold front from a passing trough over the northern tier of states stalls over KS/MO by Wednesday morning, providing continued focus for heavy thunderstorm development from eastern KS through southern IL where a Slight Risk is maintained. The frontal zone extends east over the rest of the Midwest to the eastern Great Lakes where a Marginal Risk is maintained with some areas of the Northeast trimmed with the 00Z QPF consensus being farther west. Over the northern Plains, the next trough axis enters the northern High Plains Wednesday night with activity over the Dakotas warranting a Marginal Risk. ...Southwest... A trough axis from the next reinforcing wave allows anomalous moisture over AZ/NM to spread northeast to the southern High Plains on Wednesday which warrants maintenance of the Marginal Risk with some trimming based on the 00Z consensus. Jackson Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt