Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Sun May 4 2025 Valid 12Z Wed May 07 2025 - 12Z Sun May 11 2025 ...Mid to late week heavy rainfall potential for the central Gulf Coast into the Southeast... ...Overview... A blocky pattern in the short range should finally begin to break down by Wednesday as a pair of upper lows over the East and West weaken and shift east. A stationary or slow moving frontal boundary draped across the Southeast may continue to support heavy rainfall across the region, and especially along the Gulf Coast. A shortwave dropping in from east-central Canada may briefly cut off another low over the Northeast on Friday, while the western low shifts east and eventually settles over the Southeast next weekend. This may continue the threat for showers and storms across the Southeast well into next weekend. Upper ridging over the West Coast will build into the Rockies/Central U.S. as a Pacific trough nears the West Coast next Sunday. ...Guidance/Predictability Assessment... Latest models and ensembles are in good agreement through about Friday on the overall pattern evolution during the medium range period, but still with plenty of uncertainty in the details. The models have trended towards more agreement on the second potential upper low over the Northeast, but differ in timing and placement as it exits next weekend. Also some uncertainty in the strength of additional weaker shortwave energy over eastern Canada which affects the strength of any ridging over the Northeast behind the upper low. Elsewhere, much of the guidance now shows the main core of energy from the initial West low hanging back over the Southeast, at least through next weekend, but subtle differences in the position of this would have impacts on sensible weather threats. There is some considerable timing differences with the next trough into the West by Saturday and the CMC was the outlier this cycle as it closes off a southern stream low that drifts westward into the Pacific and northern stream energy drags across the Northwest. The GFS, ECMWF, and ensemble means show more elongated troughing approaching the coast, though the ECMWF was slightly faster. The WPC progs for tonight were able to use a general model blend for Days 3-5 with enough agreement. Transitioned to 40-60 percent of the ensemble means day 6 and 7 to mitigate bigger differences in the late period forecast. ...Weather/Hazards Highlights... By Wednesday, the start of the period, the heaviest rains are likely to focus along the central Gulf Coast pooling along a frontal boundary. For the Day 4/Wednesday ERO, maintained a Slight Risk from far southeast Texas into southern Mississippi and southern Alabama, as heavy rain rates and training could cause scattered flash floods, but the potential may be limited slightly by drier antecedent conditions and higher flash flood guidance. Heavy rain could persist into Thursday along the central Gulf Coast and into parts of the Southeast, but opted for just a marginal risk right now given lingering guidance uncertainty and dry soils. Some rain and storms are likely to persist across the Southeast in general into late week and the weekend as well. Under the departing eastern upper low on Wednesday, wrapback moisture and instability on the backside of the associated surface low could lead to locally heavy rain in the sensitive terrain of the Interior Northeast. A Marginal Risk remains in place for the Wednesday (Day 4) ERO period. The upper low over the Southwest early in the period will result in below to well below normal temperatures for the Southwest and south-central Plains where daytime highs could be 15-20 degrees below normal. This should moderate with time but may still remain modestly below normal into late week for the southern Plains. Upper ridging building over the West as the upper low shifts east will allow for expanding coverage of above normal temperatures there as next week progresses, including 100 degree temperatures in the Desert Southwest. Above average temperatures will stretch into the northern tier as well, with highs reaching the 70s and 80s in the northern Plains to Upper Midwest. Slightly above normal temperatures may move into the Northeast next weekend. Santorelli Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw