Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Thu Apr 10 2025 Valid 12Z Sun Apr 13 2025 - 12Z Thu Apr 17 2025 ...General Overview... An amplified upper level trough will be in place across the East Coast for the upcoming weekend, with a surface low moving offshore the Mid-Atlantic coast that will track in the general direction of Nova Scotia by early next week. Meanwhile, an upper ridge will be in place across the Midwest states on Sunday that will support warm conditions for this time of year. An incoming upper trough across the northern Rockies will then spur surface cyclogenesis across the central/northern Plains with a cold front crossing the Intermountain West. The cold front should then reach the Deep South by Tuesday morning with surface high pressure building in behind it. Another trough is likely to reach the Western U.S. during the middle of next week, with a potential closed low near southern California by Thursday morning. ...Guidance/Predictability Assessment... The 00Z model guidance suite features good synoptic scale agreement for Sunday across the country. By Monday, the GFS is slower and more amplified with the low crossing the northern Plains, with a stronger surface low crossing the Great Lakes. The GFS is also quicker to move the coastal low near the Northeast offshore. By the end of the forecast period next Thursday, model spread increases substantially across the Pacific Northwest with additional Pacific shortwave moving in, and the closed upper low near California has trended farther west compared to the 12Z guidance. The WPC fronts and pressures forecast was derived from a multi- deterministic blend for Sunday, and then mainly GFS/ECMWF/CMC and the ensemble means going forward into the first half of next week, with means up to about 50% by Thursday. ...Weather/Hazards Highlights... The low pressure system emerging off the southern New England coast this weekend will likely keep widespread light to moderate rainfall across New England on Sunday, and widespread cloudiness from the Mid-Atlantic to the Northeast. Similar to yesterday's forecast, it does not appear likely that any areas will having flooding concerns during the Day 4 and 5 time period (Sunday and Monday), so no risk areas are currently warranted in either outlook. Having said that, there will likely be a corridor of moderate to locally heavy rainfall extending from central North Dakota to northern Minnesota and across the Upper Peninsula of Michigan during this time period as the main surface low crosses the region. Rainfall rates should be modest with that event and not enough to cause flooding issues. Elsewhere across the Continental U.S., several inches of snowfall is likely across portions of the Montana Rockies through the weekend as the upper low moves across the region. The front moving across the central Plains and Midwest to the Ohio Valley will not have much moisture or instability to work with, so rainfall associated with it should be mainly light. However, breezy conditions are likely behind the front and especially across the Great Lakes region and northern Plains where the pressure gradient will be stronger. The mid-upper level ridge axis across the Plains on Sunday will support widespread above normal temperatures from the Desert Southwest to the central and northern Plains. Highs could reach into the 90s from western Texas to eastern Colorado and western Kansas, before the cold front brings readings closer to climatology for Monday. The warmth then encompasses the Midwest to the Deep South to start the week and then it reaches the East Coast by Tuesday, with highs about 5-15 degrees above average. The cold front then brings cooler conditions back to the Eastern U.S. for the middle of the week. Hamrick 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