FOUS30 KWBC 070804 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 404 AM EDT Mon Apr 7 2025 Day 1 Valid 12Z Mon Apr 07 2025 - 12Z Tue Apr 08 2025 ...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF SOUTHERN ALABAMA AND THE WESTERN FLORIDA PANHANDLE... A cold front moves along from the border of southernmost AL/FL Panhandle eastward into the central FL Peninsula, picking up the pace with time. In the wake of the excessive rainfall/flash flooding episode near the FL Panhandle border with southernmost AL, and due to convection filling in behind the surface front and ahead of its 850 hPa position, pulled the Marginal Risk westward and introduced a Slight Risk area to account for the recent convective evolution. Precipitable water values near 1.75" will lie in the area, while ML/MU CAPE of 500-1500 J/kg advects in from the Gulf. Low- level inflow and effective bulk shear remain sufficient for convective organization. The main hindrance from a flash flood perspective is the progressive nature of the front as time marches on, particularly after midday. Considered a Slight Risk for areas farther east near the Apalachicola River in FL which could see an outflow boundary reach the region and stall while convectively active, waiting for the cold front to catch up before picking up the pace. However, QPF amongst the global and mesoscale guidance showed low chances for 3"+, so left the risk farther east as Marginal, which was coordinated with the TAE/Tallahassee FL forecast office. Roth Day 2 Valid 12Z Tue Apr 08 2025 - 12Z Wed Apr 09 2025 ...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS IN SOUTHERN FLORIDA... Deep southwest flow is expected ahead of an advancing cold front across the FL Peninsula. Precipitable water values of 1.75-2" are forecast to reside here, and ML CAPE should maximize in the 2000-3000 J/kg range per NAM guidance. Low-level inflow and effective bulk shear are sufficient for convective organization. Whether or not a flash flood risk fully materializes depends upon whether or not an East Coast seabreeze front can develop and focus convection, which could anchor convection in the large urban area of South FL as it is unlikely to progress inland within this synoptic pattern. In this sort of atmosphere, hourly rain totals to 2.5" and overall totals to 5" are possible. The 00z HREF does have some non- zero probabilities of 5"+ totals across sections of the northern Keys, while the 3"+ probabilities are more prominent along the Gold Coast. Considering the urban environment, ingredients available, and mesoscale guidance signal, added a Marginal Risk to South FL and the Upper Keys as a precaution as isolated to widely scattered flash flooding appears possible. Roth Day 3 Valid 12Z Wed Apr 09 2025 - 12Z Thu Apr 10 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ...Southern Illinois... Conceptually, there is a non-zero threat of heavy rainfall in and near southern IL Wednesday evening as precipitable water values rise near to above 1" within a region with 1000-500 hPa thickness near 5550 meters, implying a completely saturated troposphere. MU CAPE is expected to rise above 250 J/kg per NAM guidance, which tends to be underforecast at this time range. The area will still be attempting to dry out from recent heavy rainfall/ saturated soils. However, there is only about a six hour window for heavy rain concerns to materialize near the parent cyclone's associated frontal boundary before it moves through. There is the potential for hourly rain totals to maximize near 1.5". The guidance is this time range QPF-wise is underwhelming, so no risk area was depicted. However, this may change as we move closer in time into the high resolution guidance window. Roth 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