Extended Forecast Discussion NWS Weather Prediction Center College Park MD 248 PM EDT Fri Apr 4 2025 Valid 12Z Mon Apr 07 2025 - 12Z Fri Apr 11 2025 ...General Overview... It remains good news that major improvement is coming to the areas that are getting hammered by extremely heavy rainfall and severe weather Friday and into this weekend. An amplifying upper level trough over the Great Lakes and Ohio Valley region will accelerate a cold frontal passage, with the wavy boundary exiting the East Coast on Monday. There is however a threat for plowable snow/ice over the northern tier of the Northeast through Monday as a supporting and amplified upper trough and wavy lead fronts work through. Otherwise, drier and much cooler conditions will arrive behind it and likely remain through much of next week. Meanwhile across the western half of the country, a couple of shortwaves will pass through the northwestern states with some organized precipitation overtop a mean ridge position. This upper level ridge is expected to build over the Great Basin then Rockies later next week, to be sandwiched between a downstream trough across the east- central U.S. and an amplifying trough off the West Coast. ...Guidance/Predictability Assessment... Latest model guidance indicates good overall agreement across the Continental U.S. and vicinity for early next week and a multi- deterministic model blend works well as a starting point for this time frame. By midweek, recent GFS and to a lesser extent GEFS runs through the 06 UTC cycle become faster and stronger with the upper pattern and low pressure system developing across the Plains, and this continues going into the end of next week as well. Examination of AIFS machine learning guidance from the ECMWF and teleconnections with positive/negative 500mb height anomalies over the North Pacific and North Atlantic support the idea of a slower trough evolution and progression across the Eastern U.S. for the second half of next week. This falls more in line with the ECMWF/ECENS/CMC/Canadian ensemble mean solutions and the WPC forecast follows this preferred approach, in contrast to the faster GFS runs. However, the 12 UTC GFS has trended more amplified and slower. There is also growing model spread with shortwave energy approaching the Pacific Northwest late in the period, so an ensemble mean approach also works well for this region by Thursday into next Friday. Given uncertainties, opted to shift the WPC forecast blend to at least 70% ECMWF/Canadian ensemble means and NBM over/near the lower 48. This plan maintains good WPC product continuity over our nation. ...Weather/Hazards Highlights... The heavy rainfall potential decreases quite a bit to begin next week in comparison to what is expected this weekend. However, there will still be an axis of deep moisture over the coastal plain to coastal areas of the Southeast states ahead of the cold front, with areal 1-2+ inch totals possible from northern Florida and southern Georgia to the Hampton Roads area of southeast Virginia, mainly between 12Z Monday and 00Z Tuesday, where a Marginal Risk of excessive rainfall remains in effect for the Day 4 ERO period. With the exception of the central and southern Florida Peninsula, the threat of heavy rainfall should be over by Tuesday across the remainder of the country with no risk areas needed. If future models trend higher with QPF over South Florida during this time, it is possible a Marginal Risk area may eventually be needed there. The WPC Hazards Outlook added a threat for plowable early April snow/ice across the northern tier of the Northeast as enhanced locally by terrain through Monday with approach of an amplified upper trough and with lead surface fronts and wrapping moisture. Elsewhere across the country, rain and mountain snow makes a return to western Washington and Oregon courtesy of onshore flow and a couple of shortwave trough passages by early next week, but this does not look like a major event at this time. Light precipitation crosses the Northern Plains and Midwest into mid-late next week, and the next good chance of rainfall may reach into the Eastern U.S. by next Friday as an uncertain surface low may develop. In terms of temperatures, much cooler conditions are coming for the Eastern U.S. after the strong cold front exits the East Coast Sunday night/Monday morning. Afternoon highs are likely to be on the order of 15 to perhaps 25 degrees below early April averages on Tuesday from the Ohio Valley to the eastern Great Lakes, compliments of the upper low overhead. Readings return closer to average by late in the week for the East Coast states. Meanwhile, a warm pattern is expected for the Western U.S. through the week with both daytime highs and overnight lows about 10-20 degrees above average, with the greatest anomalies over the Great Basin. Hamrick/Schichtel 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