Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 PM EDT Wed Apr 9 2025 Valid 12Z Sat Apr 12 2025 - 12Z Wed Apr 16 2025 ...General Overview... An amplified upper level trough will be in place across the East Coast for the upcoming weekend, with a surface low off the Mid- Atlantic coast likely tracking a little south of Nova Scotia by early next week. Meanwhile, an upper ridge crossing the central U.S. during the weekend will support very 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 by Sunday with a cold front crossing the Intermountain West. The cold front should then reach the south-central and eastern U.S. by Tuesday as the leading upper ridge continues eastward. The front's supporting upper trough should reach the East by next Wednesday. Another trough is likely to reach the West Coast region during the Tuesday to Wednesday time period, but its evolution has higher uncertainty. ...Guidance/Predictability Assessment... By Sunday the latest models still develop some spread for the finer details of the upper trough/possible embedded upper low crossing the northern Rockies, though the envelope has been gradually narrowing toward an intermediate solution. The GFS/ICON/CMC still lean toward a slightly farther south upper low crossing Montana into the Dakotas while other dynamical and machine learning (ML) guidance either tracks the upper low near the northern Montana border or waits to close off an upper low farther to the east. By Monday the ML models offer reasonable support for the upper low and occluded surface system to reach near or just west of Lake Superior. Latest GFS runs stray to the slower side of the spread as this system continues into Canada. However there is good large scale agreement for the overall upper trough reaching the East by next Wednesday. Over the eastern Pacific into the West, there is continued spread for a leading upper low (composed of energy from the southern periphery of the weekend shortwave) that may reach the Southwest around Tuesday. The GFS/CMC lean on the slower side of the spectrum for this feature. Then guidance continues to signal that flow within the next upper shortwave should split, but with some differences in the exact proportion that digs southward versus continuing into the West. GEFS/ECens means and along with the latest ECMWF/GFS runs have support from one ML model cluster, with a shortwave reaching western Canada and the Northwest U.S. while the remaining energy reaches offshore California. A couple 00Z ML models had more ridging over the Northwest though. For the system affecting the East this coming weekend, guidance continues to show various detail differences. In particular the GFS has been leaning to the northwest/north side of the spread for the surface system and moisture extent while CMC runs show a more open trough versus the closed low in most other solutions. Based on guidance comparisons and continuity, an early-mid period forecast consisting of 40 percent 00Z ECMWF and 20 percent each 06Z GFS, 00Z UKMET, and 00Z CMC provided a good starting point to reflect majority themes or an intermediate scenario as appropriate. 20-40 percent inclusion of the 06Z GEFS/00Z ECens means helped to downplay less confident details by next Tuesday-Wednesday. ...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 the Northeast U.S., especially on Saturday with the heaviest rainfall beginning to exit the Cape Cod region. Higher elevation snow is likely for the northern Appalachians through the weekend with several inches of accumulation possible. With most of the heaviest rainfall expected on Friday and guidance showing a lot of spread for where any locally enhanced rain could fall on Saturday/Day 4, that day's Excessive Rainfall Outlook depicts no risk areas. The Sunday/Day 5 ERO also has no risk areas, though there will likely be a swath of moderate rainfall across the northern tier states with the surface low moving through. Flow behind this system will support a broad area of strong and gusty winds across the eastern Rockies into parts of the Plains on Sunday. Elsewhere across the Continental U.S., expect several inches of snowfall across the higher terrain of the Northern Rockies through the weekend as the upper trough/possible embedded low moves across the region. As the northern Plains system tracks into Canada, the front moving across the central Plains and Midwest into the East Monday-Tuesday will not have much moisture or instability to work with, so rainfall associated with it should be mainly light. There may be an increase in shower coverage across portions of the southern Plains by the middle of next week as a potential wave of low pressure develops along the front, but this activity does not look impressive at this time. Portions of the East may see brisk winds next Tuesday-Wednesday. The mid-upper level ridge crossing the central U.S. this weekend will support widespread above normal temperatures from the Desert Southwest to the central and northern Plains. Some highs may reach 20-25 or so degrees above normal, corresponding to temperatures into the 90s from western Texas to eastern Colorado and western Kansas, before the cold front brings readings closer to climatology for Monday. Some daily records will be possible, especially on Saturday. The warmth will encompass the Midwest to the Deep South to start the week and then reach the East Coast by Tuesday, with highs about 5-15 degrees above average. Before then, widespread cloud cover over the weekend will maintain cooler than average highs across the Eastern U.S. before moderating. The next upper trough reaching the East by Wednesday may bring another cool day then, with the central Appalachians/eastern Great Lakes possibly seeing highs at least 10 degrees below normal. To the west, another upper ridge should spread above normal readings from the West Coast into the northern and central Plains during early-mid week with decent coverage of plus 10-15 degree anomalies for highs. Rausch/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