Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 PM EDT Thu May 1 2025 Valid 12Z Sun May 04 2025 - 12Z Thu May 08 2025 ...Blocky pattern with closed lows over the West and the East with areas of heavy rainfall potential... ...Overview... The forecast continues to call for a blocky pattern over the Lower 48 next week. The dominant features will be two closed upper lows, one over the West/Southwest and one over the East, that will both slowly drift around weakening through Wednesday/Thursday. These systems are expected to produce areas of significant rainfall over portions of the Central and Southern Plains, Northeast, and Mid- Atlantic and high elevation snows in the West. Eventually, the eastern upper low should interact with a northern stream trough that will swing across southern Canada, resulting in the low being swept up towards the Canadian Maritimes late next week. The Western low will likely remain isolated as it drifts east over the Plains and weakens on Wednesday. The remnants of the Western low may eventually combine with another trough developing over the East Coast late Thursday into Friday. By Wednesday, another trough and frontal system will approach the West Coast. ...Guidance/Predictability Assessment... Overall, model guidance is in fairly good agreement on the overall pattern. There have been some shifts in the guidance since the overnight forecast that will affect the sensible weather, the most impactful one being an eastward shift in the upper low/surface frontal system that will bring rain to the Plains Tuesday through Thursday. This eastward shift is due to a slightly more westward position of the western upper low, which will bring heavy rain further into Texas and Oklahoma than the previous forecast. There is considerably more uncertainty in the East, which will depend on how the upper low interacts with the northern stream. The 06Z GFS continued to be the outlier with a flatter and faster northern stream that interacts very little with the upper low, while all other guidance is still depicting a more amplified northern stream that absorbs the eastern low eventually. For the afternoon forecast, the amplified northern stream consensus was used, which also maintains continuity from the overnight forecast and is in line with new 12Z guidance. WPCs model blend consisted of the 06Z GFS and 00Z ECMWF/CMC/UKMET for the first two days. By Day 5 (Tuesday), the weight on the 06Z GFS was reduced and ensemble means from the GEFS and ECENS were added to the blend in increasing amounts through the end of the period. ...Weather/Hazards Highlights... Early next week, two occluded frontal systems are expected to bring moderate to locally heavy rainfall to portions of the West and East. In the West, anomalous moisture accompanying the upper low will support heightened precipitation from the Great Basin to the Central and Southern Rockies and Plains. Precipitation will be initially triggered by the surface frontal system, which will push across the Intermountain West on Sunday then become stationary over the Plains next week. Once the system stalls, moisture will continuously pool over the Plains, which will likely result in a multi-day heavy rainfall event across the Central and Southern Plains. The heaviest precipitation is forecast to fall over the Southern Plains Monday into Tuesday, then spread into the Lower Mississippi Valley Wednesday and Thursday. Portions of the Plains states will be especially vulnerable to heavy rain/flooding due to recent heavy rains and saturated soils. This activity is highlighted in the Day 4-5 Excessive Rainfall Outlooks (EROs) with a Marginal Risk area on Sunday and a Slight Risk area on Monday focused on eastern New Mexico and the Texas and Oklahoma panhandles. Under the eastern upper low, the frontal system will very slowly push east across the East Coast, resulting in a stream of onshore moisture over the Mid-Atlantic and Northeast. This pattern will result in persistent precipitation across these regions through Tuesday. Initially, rainfall could be beneficial and bring some relief to drought conditions, but repeated rounds of rainfall could produce locally heavy totals and may result in localized flooding in urban and poor drainage areas. The Day 4-5 EROs show a Marginal Risk area across these regions on both Sunday and Monday. By Wednesday, the frontal system should accelerate to the east as the upper low interacts with the northern stream, shifting precipitation farther into the Northeast. The northern High Plains in particular will see well above normal temperatures on Sunday, with some plus 15-25 degree anomalies for highs. Temperatures will steadily moderate as this area of warmth migrates eastward early next week. In contrast, the upper low tracking into the Southwest will bring much cooler temperatures to the region. Highs should be 10-20 degrees below normal on Sunday- Monday, with some record cold highs possible near the upper low's path. The Southwest will slowly trend closer to normal after midweek. Persistent clouds and rainfall should keep the southern High Plains below normal for highs as well. The Northwest will see a warmer trend next week, with some highs reaching 10-15 degrees or so above normal. Over the East, locations under and southwest of the Ohio Valley upper low should see moderately below normal highs Sunday-Monday and then some moderation. The Northeast will tend to see above normal lows. Dolan/Rausch 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