Extended Forecast Discussion NWS Weather Prediction Center College Park MD 232 PM EDT Sun Apr 6 2025 Valid 12Z Wed Apr 09 2025 - 12Z Sun Apr 13 2025 ...General Overview... It remains well evident in guidance that a large upper trough that will be in place across the Northeast U.S. early in the week is forecast to lift out of the region by Thursday. An amplifying shortwave trough originating from south- central Canada is expected to amplify as it drops southeast across the Ohio Valley, and thus support a surface low from the Midwest to the Mid-Atlantic coast to close out the work week and emerging off the coast next Saturday. Meanwhile, an upper level ridge builds across the Intermountain West and Rockies Thursday into Friday, and then shifts eastward to the Plains by next weekend. With the ridge departing the West, an upper trough approaches from the Pacific Northwest and supports a slow moving frontal boundary across the Intermountain West. ...Guidance/Predictability Assessment... The WPC medium range guidance suite was primarily derived from a composite blend of seemingly reasonable and best clustered guidance from the 00 UTC ECMWF/UKMET/Canadian models and WPC continuity valid for Wednesday into Friday morning. Forecast spread increases heading into next weekend and a composite of the overall compatible GEFS/ECMWF/Canadian means and WPC continuity offers a good forecast basis while tending to mitigate much of numerous smaller scale system details as consistent with individual system predictability. Latest 12 UTC guidance seems in line, including some reasonably favorable trends from the GFS. ...Weather/Hazards Highlights... The weather pattern continues to look uneventful in terms of heavy rainfall prospects for the middle of the week, with no risk areas currently needed for the excessive rainfall outlooks for both days 4 and 5. Having said that, a swath of mainly light to moderate rainfall is expected from the Midwest to the Ohio Valley, and perhaps a second area of rainfall developing across the Tennessee River Valley on Thursday as the surface low and front moves through. Even though forecast rainfall totals are not expected to be heavy, the ground will likely still be quite saturated for many of those areas after the prolific rainfall lately, so that is something that will continue to be monitored. Colder high pressure held over the Northeast interior in advance of the system may allow for some terrain focusing snow chances. A surface low to deepening coastal low may begin to develop near the Mid- Atlantic Coast by Friday night and result in higher rain chances and breezy conditions from Virginia to New England into next weekend. Given flow amplitude and trends, the system offers potential for enhanced rain up the coast and to be a maritime hazard to monitor. Elsewhere across the country, periods of moderate rain and mountain snow return to western Washington and Oregon courtesy of onshore flow and a couple of shortwave trough passages mid to late week, but these don't look like major events at this time. Light snow then reaches the higher elevations of the northern Rockies by next weekend as the moisture moves inland. In terms of temperatures, the coldest day of the forecast period is expected on Wednesday with high temperatures running about 10-20 degrees below average. A moderating trend commences by the end of the week as the upper trough lifts out of the Northeast states. Looking ahead to next weekend, lows should be near average while daytime highs remain slightly below average. Meanwhile, a warm pattern is expected for the Western U.S. through the end of the week with both daytime highs and overnight lows about 10-20 degrees above average, with the greatest anomalies over the Great Basin. These milder conditions then reach the central and northern Plains by next weekend as the ridge shifts eastward. 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