Extended Forecast Discussion NWS Weather Prediction Center College Park MD 313 PM EDT Fri Mar 28 2025 Valid 12Z Mon Mar 31 2025 - 12Z Fri Apr 04 2025 ...Emerging heavy rain and severe threat for Lower Mississippi, Tennessee, and Ohio Valleys for midweek and beyond... ...Overview... A parade of systems should bring periods of active weather to much of the U.S. next week. A cold front into the East next Monday should bring widespread rain and thunderstorm chances, with some locally heavy rain across the South. Another system into the West should ultimately lead to a surface low emerging into the Plains around midweek and tracking towards the Great Lakes. Widespread moderate to heavy rain will accompany this second cold front in the east-central CONUS, while late-season snow is possible in the northern tier. The West should stay relatively cool underneath of almost persistent troughing, while the central to eastern U.S. experiences periods of normal to above normal temperatures. ...Guidance/Predictability Assessment... Model guidance is reasonably agreeable at the start of the medium range period, with a shortwave moving through the Midwest to Northeast Monday-Tuesday (though the 00Z UKMET was a slow outlier) and an upper low offshore of the Pacific Northwest. The latter will send energy eastward reaching the Plains by midweek, potentially forming a weak closed low, along with a reasonably strong surface low that shows typical timing and placement differences as it tracks from the central U.S. to the Upper Great Lakes by Thursday. Upper ridging in the East and mean troughing across the West looks to set up by later week. The troughing across the West has shown the most model differences over the past couple of days. Finally the 06Z GFS and now the newer 12Z GFS is showing more agreement with the larger ECMWF/CMC cluster of guidance by around midweek (the 00Z GFS and older GFS runs were pulling significant amounts of energy and troughing into the eastern Pacific at that time). However, the 00Z ECMWF appeared to pull a different shortwave southward along the West Coast Thursday-Friday, which really only the Pangu AI/ML model agreed with--other AI models and the CMC showed the trough axis farther east. So did not favor the 00Z EC as much during the late period. Thus the WPC forecast was based on a blend initially favoring the 00Z ECMWF with lesser proportions of the 06Z GFS and 00Z CMC early in the period. As the period progressed, lessened the proportion of deterministic models in favor of the ensemble means to half Day 6 and more Day 7 as spread increased. Notable edits to the NBM included lowering QPF in the West where the older GFS runs that were not favored seemed to be contributing heavy QPF into the blend while the EC/CMC and their means showed less. QPF increased from continuity in the east-central U.S. as models started to be more agreeable with heavy amounts for the latter half of next week. ...Weather/Hazards Highlights... A cold front moving into the East should allow for widespread rain and thunderstorms across much of the Eastern Seaboard on Monday. The best chance for locally heavy to excessive rainfall should be over parts of the Southeast where more instability will allow for heavier rain rates, so a Marginal Risk remains in place for the Day 4/Monday Excessive Rainfall Outlook. Locally heavy rain may also occur farther north from the Appalachians to Mid-Atlantic and Northeast. The Storm Prediction Center also suggests strong to severe weather is possible from the Southeast into the Mid- Atlantic as well on Monday. Expect multiple systems to bring rain and higher elevation snow to the West during the period. The best precipitation focus looks to be across Northern California on Monday, and a Marginal Risk remains in place for coastal regions into far southwest Oregon for the Day 4/Monday ERO with a weak atmospheric river. Precipitation with some higher elevation snow will spread through the Intermountain West and Rockies Monday-Tuesday, while the pattern also supports high winds focused from the central Great Basin into the central Rockies. As the upper trough in the West reloads into mid and late next week, it will support a surface low pressure system forming in the central U.S. by Wednesday with widespread thunderstorms across the east-central U.S. in its warm sector. SPC indicates another round of severe weather from the south-central U.S. into the Mid-South and Ohio Valley on Wednesday, and heavy rainfall is also a concern. The low is forecast to move northeastward Thursday-Friday but leave a wavy front behind across the Mid-South to Ohio Valley, causing likely multiple rounds of heavy rain over similar areas, enhancing flooding concerns. Additionally, some April snow is likely on the backside of the low across the northern Plains and Upper Midwest Tuesday-Wednesday and spreading into the Interior Northeast Wednesday-Thursday. Meanwhile some modest rain and snow could continue across the West throughout next week, though with rapidly increasing uncertainty in the details after early next week. The warm sector ahead of the front crossing the eastern half of the country into Monday will feature well above normal temperatures. Expect plus 10-20F anomalies for highs and up to plus 20-25F anomalies for morning lows. Near to below normal readings will progress eastward behind the eastern U.S. front, with precipitation keeping some northern Plains to Great Lakes locations 5-10F or so below normal for highs into Tuesday. Temperatures may rebound back above normal over the southern half of the Plains on Wednesday with the warming trend spreading back into the East thereafter. Periods of unsettled weather will keep the diurnal spread over the West Coast states more narrow than usual, with cool highs and near normal lows. Tate/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