Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Fri Apr 25 2025 Valid 12Z Mon Apr 28 2025 - 12Z Fri May 02 2025 ...Potent Rockies to Central U.S. Spring Storm expected early next week... ...Overview... The primary focus early next week will be on ejecting Rockies upper trough energy and associated northern Plains through Upper Great Lakes surface system, bringing some heavy rain potential to the northern tier and possible severe weather to central/east- central U.S. The northern part of this system will continue onward but the trailing part of the front should stall and develop some waviness ahead of weaker southwestern shortwave energy, providing a focus for enhanced central U.S. rainfall around midweek. Upstream energy should push the evolving system and rainfall eastward thereafter, with an upper trough axis reaching the east-central states by Friday. A trailing upper ridge should move into the West after early Wednesday, likely followed by a trough/cold front nearing the West Coast by Friday. ...Guidance/Predictability Assessment... A 12Z/18Z operational model composite provided a reasonable depiction of significant features during the first half of the period. There is decent clustering with only typical detail variations for northern Plains low pressure that should track across the Upper Great Lakes and then eastern Canada, with the trailing front ultimately stalling over the Plains as weak shortwave energy lingers over the southwestern U.S. By the latter half of the week there is still better than average agreement among model/ensemble guidance that incoming shortwave energy should eject the southwestern shortwave, leading to a surface wave reaching the vicinity of the eastern Great Lakes by early Friday. However shortwave detail uncertainties increase at that time and machine learning (ML) models show more spread for the eastern U.S. surface pattern, so confidence is a bit lower than what might be suggested by the dynamical model/ensemble clustering. Meanwhile there are also developing differences with the upper trough nearing the West Coast by next Friday. The most prominent difference is that GFS runs are faster and less amplified than the dynamical/ML model consensus for a majority of the trough. The GEFS mean is closer to the majority scenario. While a leading mean ridge moves over the West late in the week, there may be weak trough/upper low energy that reaches the Southeast/Great Basin but with very low confidence for specifics. Late week preferences sided mostly with the 12Z ECMWF and the 18Z GEFS/00Z ECens means given comparisons along the West Coast, while this solution represented consensus over the East. ...Weather/Hazards Highlights... The early week Rockies into central U.S. storm will bring high elevation snow to the north-central Rockies along with a heavy rainfall threat farther east along the northern tier in association with anomalous moisture and favorable dynamics/surface focus. The Day 4/Monday Excessive Rainfall Outlook depicts a Marginal Risk area that includes portions of the northern High Plains into Upper Midwest. Some locally heavy rain may fall farther south over the Mississippi Valley and vicinity but without a sufficiently clear signal to merit a risk area for now. By Tuesday into early Wednesday the Plains part of the system's trailing front should stall and provide a focus for trailing/repeat convection. The Day 5/Tuesday ERO reflects the runoff threats with a Marginal Risk area from central Texas into the Lower Ohio Valley. Meanwhile the Storm Prediction Center continues to monitor for severe weather threats over central/east-central U.S. Monday-Tuesday. The central U.S. heavy rain potential will likely continue through the rest of Wednesday before upper dynamics and surface waviness/fronts progress into the East with somewhat lesser rain totals. Farther west, shortwave energy pushing through the West should spread rain and some high elevation snow from the Northwest through the northern and central Rockies over the course of the week. Very warm temperatures over the Plains/Mississippi Valley on Monday will progress into the East ahead of an advancing cold front, with highs up to 10-20F above normal and morning lows even a little more anomalous. The wavy front may not reach parts of the Southeast/Mid-Atlantic, where temperatures could remain somewhat above normal through Friday. Cool readings from the Southwest to northern High Plains on Monday should moderate as the air mass continues eastward. Then expect a trend to above normal temperatures over the West mid-late week as an upper ridge builds in. Highs may reach 10-15F above normal from the Pacific Northwest into northern Rockies. Rausch 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