FOUS30 KWBC 291900 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sun Mar 29 2026 Day 1 Valid 16Z Sun Mar 29 2026 - 12Z Mon Mar 30 2026 ...16Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 2 Valid 12Z Mon Mar 30 2026 - 12Z Tue Mar 31 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ...19Z Update... No changes were needed due to sufficiently similar model guidance in the 12Z runs. Wegman ...Previous Discussion... An uptick in convective activity is expected Monday night into Tuesday morning across portions of MI into western PA/NY. There is a strong surge of moisture and instability, and thus locally heavy rainfall is possible. Overall it seems like the better chance of localized flash flooding is after 12z Tuesday as the duration of rain makes hydrologic conditions more sensitive by then. So we will hold off on introducing any day 2 risk area and let the day 3 Marginal cover the threat. But we will continue to monitor trends as the event gets more in range of the high res models today. Chenard Day 3 Valid 12Z Tue Mar 31 2026 - 12Z Wed Apr 01 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE GREAT LAKES INTO NORTHERN NEW ENGLAND... ...19Z Update... Forecasted rainfall across portions of the Marginal Risk area, especially east of the lower Great Lakes into New England, have increased with the latest 12Z guidance. Impressive moisture advection characterized by IVT values exceeding 750 kg/ms in spots will move northeast along a slow-moving front across the Great Lakes. This will allow near record amounts of atmospheric moisture for this time of year, with PWATs exceeding 1.25 inches at times to move into the Marginal Risk area. Instability will increase towards the south and west, but drier antecedent soil conditions and weaker forcing should cancel out those supporting meteorological factors along the Mississippi River and the Ozarks. The Marginal Risk was left in place, with a few minor expansions into northern New Hampshire and the Chicago area. The greatest concerns within the Marginal are across upstate New York, where advancing instability will meet with the best forcing. Ultimately the instability staying shy of 1,000 J/kg MUCAPE should sufficiently prevent more widely scattered instances of flash flooding (i.e. a Slight Risk) by limiting rainfall rates. The area will need to continue to be monitored as the event moves into the CAMs range. Wegman ...Previous Discussion... A stationary front positioned over NY will likely be a focus for scattered convection to start the period Tuesday morning. The front is not forecast to move much during the day, likely supporting periodic rounds of scattered showers and thunderstorms. An area of low pressure riding along the front should increase forcing and convergence by Tuesday evening, resulting in an uptick in rainfall coverage. Moisture parameters are impressive with this system...PWs are forecast to be near late March to early April max values, and IVT increases above the climatological 90th percentile. Instability is more marginal, and will likely reduce max rainfall rate potential and act as a limiting factor for flash flooding. However, there is some instability forecast in the morning, and by evening the increasing forcing/convergence could help offset decreasing instability. Thus while not widespread, some localized hourly rainfall around 1" seems plausible. Model consensus rainfall magnitudes are generally in the 1-2" range, although with multiple rounds likely, there is a potential for more localized swaths getting into the 2-4" range. These higher amounts are most likely over portions of far northeast OH, far northwest PA and into southwest NY...near the stationary front and within a corridor where instability has a better chance of persisting. A bit farther northeast into upstate NY and VT, some snow melt contribution could also aid in minor runoff concerns. Farther southwest over IN and OH instability is higher supporting greater rainfall rates, but duration should be shorter with a quicker frontal progression. Soil and streamflow conditions are more conducive for flood impacts over portions of OH and IN, but dry out with southwest extent into IL and MO. Thus while convection will extend into these latter areas as well, for now we will stop the Marginal risk near the IL/IN border. Overall the primary threat is for localized flooding in areas where training, or multiple convective rounds, occur near the stationary front...or where higher short duration rates intersect sensitive urban areas. Chenard 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