FOUS30 KWBC 041558 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1058 AM EST Wed Nov 4 2026 Day 1 Valid 16Z Wed Nov 04 2026 - 12Z Thu Nov 05 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR A PORTION OF SOUTHEAST FLORIDA AS WELL AS FOR PORTIONS OF THE OHIO AND TENNESSEE VALLEYS AND SOUTHERN APPALACHIANS... 16Z Excessive Rainfall Discussion... Composite radar clearly depicted a slow-moving cold front extending north to south across the Ohio and the Tennessee Valleys with showers and some embedded thunderstorms in the warm air ahead of the front. 12Z soundings showed the pre-frontal airmass characterized by precipitable water values of 1.75+ inches feeding into the Tennessee Valley from the south with sufficient instability to support local downpours but the dry antecedent conditions should mitigate the overall flash flood threat to the point where a Marginal risk remains appropriate. In southeast Florida...the on-shore flow regime will continue to support localized downpours in and near the urban corridor into the late afternoon or early evening. Bann Previous Excessive Rainfall Discussion... ...Tennessee and Ohio Valleys and Southern Appalachians... A slow-moving cold front moving across the lower Ohio and Tennessee Valleys this morning will continue to push east into the upper valleys and southern Appalachians today. Training showers with a few embedded thunderstorms are expected to persist through the day. Those thunderstorms could produce rainfall rates of 1-1.5 inches at times, which could cause an isolated flash flooding threat. This is mostly due to the influx of abundant Gulf moisture with PWATs to 1.75 inches. Working against significant flooding are the very dry antecedent soil conditions from an entire second half of October with very little to no rain. Instability will also limit rainfall rates, as values in most of the Marginal Risk area struggle to get even to 1,000 J/kg. The Southern Appalachians could have a bit higher flash flooding risk due to the terrain influences and added upslope wringing out additional rainfall on those local areas. ...Southeast Florida... A final day of continued onshore light easterly flow with an abundance of tropical moisture will once again promote any storms having a heavy rainfall and consequent flash flooding risk today. As has been the case the past few days, the storms will form over the straits between the northwest Bahamas and Florida, then drift east towards the urban corridor between West Palm Beach and Miami. This area has been in this pattern for over a week, so the soils in this normally flood-resistant area are fully saturated. Thus, any new rainfall will immediately convert to runoff. While storm coverage is expected to be much more isolated than previous days, the potential for flash flooding development remains high enough to keep the inherited Marginal Risk ongoing with few changes. Fortunately by tomorrow, developing northerly flow will advect significantly drier air into south Florida, allowing the area to begin a much drier period. Wegman Day 2 Valid 12Z Thu Nov 05 2026 - 12Z Fri Nov 06 2026 The probability of rainfall exceeding flash flood guidance is less than five percent. Wegman Day 3 Valid 12Z Fri Nov 06 2026 - 12Z Sat Nov 07 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTHERN NEW ENGLAND... Only minor tweaks were made to the inherited Marginal Risk area for southern New England, NYC and Long Island on Friday. There remains considerable uncertainty as to where the western edge of the rain shield will be, with the best forecast looking like it will be right over NYC and the lower Hudson Valley. A wave may try to push the plume of heaviest rain west across NYC Friday afternoon, before the rain shield wraps up and pushes everything east out to sea. There's more certainty that eastern Long Island through southern New England will be stuck in the axis of heaviest rainfall for much of the period. Despite a prolonged period of dry weather going into this event, as well as limited instability generally sub-500 J/kg, PWATs around 1.5 inches, urban, and upslope enhancement should work to cancel those out. This will result in isolated instances of flash flooding in urban and poor-drainage areas. Any additional eastward shifts in the plume would remove the NYC metro from the Marginal with future updates. Wegman Day 4 and Day 5 Valid 12Z Sat Nov 07 2026 - 12Z Mon Nov 09 2026 The probability of rainfall exceeding flash flood guidance is less than five percent. Pereira 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 $$