063 FXUS02 KWBC 010658 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM 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... Models and ensembles continue to show a blocky pattern becoming established over the Lower 48 by around the start of the period early Sunday and continuing over most areas into next Thursday. The dominant features will be two upper lows, one that likely drifts from California to the central High Plains and the other over or near the Ohio Valley early in week and then possibly lifting out thereafter. These systems will produce some significant rain and high elevation snow over the West plus heavy rain over parts of the Plains, and farther east another area of rain that should be heaviest over portions of the Mid-Atlantic/Northeast. The majority of guidance shows an East Pacific upper ridge tracking across western/central Canada, ultimately leading to some eastern Canada into Northeast U.S. troughing that could help to eject the eastern upper low. Then the leading edge of an upstream trough should reach the Northwest by midweek or so, along with a leading cold front. ...Guidance/Predictability Assessment... 18Z and 00Z GFS trends have now greatly improved overall guidance agreement for the upper low over or near the Ohio Valley early next week. There are still some typical position differences to be worked out, but current clustering finally offers good overall forecast confidence after a number of days of wildly divergent and inconsistent solutions over the East that were more reminiscent of model behavior from 20 years ago. Meanwhile guidance consensus looks fairly stable for the Southwest upper low, but some individual solutions have starting showing a little more variability with individual vort lobes, especially from the southern edge of a remaining northern stream trough. A composite of the 18Z GFS and 12Z ECMWF/CMC/UKMET offered a good starting point for Sunday-Monday. A couple issues arise by Tuesday-Thursday. Recent GFS runs and to some degree the GEFS have been showing much flatter flow across southern Canada in contrast to a ridge that crosses the far northern tier U.S. and western- central parts of southern Canada in most other dynamical and machine learning (ML) guidance. The majority pattern leads to some eastern Canada into Northeast U.S. trough amplification by next Thursday. This troughing could encourage the departure of the initial Ohio Valley upper low (which displays increasing north-south spread in the guidance along with spread for its departure speed). Flatter flow in the GFS leads to slower upper low timing. Within the non-GFS cluster there are meaningful differences for the character of eastern Canada trough amplification, favoring increasing ensemble mean input to complement remaining operational runs. To reflect preferences for this time frame, the forecast blend removed the GFS while increasing total 12Z ECens/CMCens weight to 60 percent and splitting ECMWF input equally between the 12Z and 00Z/30 runs. ...Weather/Hazards Highlights... Confidence continues to increase with the forecast of an Ohio Valley upper low and wavy East Coast front early next week, supporting some areas of moderate to locally heavy rainfall. The Days 4-5 Excessive Rainfall Outlooks covering early Sunday into early Tuesday depict a Marginal Risk area over parts of the northern Mid-Atlantic and Northeast where the persistent pattern should direct the best moisture. Overall guidance signals suggest Day 5/Sunday could have the higher rainfall totals over northern Mid-Atlantic urban areas and thus requiring closer monitoring going forward. Rainfall leading into and during the period will initially be beneficial given the drought conditions over some areas, but could trend less favorable with time if sufficiently heavy on a localized basis. Additional rain should fall over the Northeast through or beyond midweek, with decreasing confidence in specifics given spread of the upper low and how northern stream flow may interact. The upper low drifting across the Southwest/Four Corners and a leading frontal boundary will initially produce a broad area of rain and high elevation snow across the Interior West and Rockies plus support increasing heavy rain potential over the southern half of the Plains Monday onward. Guidance maintains some signal for enhanced rainfall over the sensitive terrain over and near the eastern half of New Mexico on Day 4/Sunday, so that ERO maintains continuity with a Marginal Risk area. Continued eastward drift of the upper low and leading wavy surface front by Day 5/Monday should generate heavier rainfall over the southern High Plains at that time. The best model clustering and first-guess guidance recommend a Slight Risk area emphasizing northwestern Texas and far eastern New Mexico with a little added extent to the north. The surrounding Marginal Risk area extends somewhat northward along the eastern slopes of the Rockies. Expect southern Plains heavy rain potential to continue through midweek. During the Days 4-5 period there are some indications for enhanced rainfall over other areas of the Interior West/Rockies/High Plains but with not enough consensus to suggest a risk area at this time. The northern High Plains in particular will see well above normal temperatures on Sunday, with some plus 15-25F 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 10-20F 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 10-15F 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. This is the final forecast of my career. It has been an honor and a source of great satisfaction to work in NOAA/NWS for the past 30+ years while witnessing the tremendous advances in weather forecasting over that time. Now it's on to a retirement that hopefully offers as much excitement as the weather. Best wishes to all, and to all happy forecasting! 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 $$