Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Sun Mar 23 2025 Valid 12Z Wed Mar 26 2025 - 12Z Sun Mar 30 2025 ...Overview... Expect the amplified western ridge/eastern trough upper pattern lingering into Wednesday to move steadily eastward while trending a little flatter, as dynamics from a strong East Pacific upper trough Wednesday-Thursday (supporting a storm system off the Pacific Northwest coast) push into the western and central U.S. With a slightly slower trend noted in the guidance, the mean ridge should reach the East by next weekend. Expect very warm temperatures under the western upper ridge through midweek or so with some daily records possible. Anomalous warmth will then move into the Plains, followed by moderation farther east. Upper dynamics and the leading front arriving from the Pacific will bring rain and high elevation snow to the Northwest mid-late week, with another system possibly approaching by next Sunday. A southern tier shortwave will support the threat of locally heavy rainfall over parts of Texas late in the week. This moisture and additional Gulf inflow may combine to spread a broader area of precipitation over parts of the Plains and east-central U.S. late week into the weekend, in association with Plains through Upper Midwest low pressure. ...Guidance/Predictability Assessment... The Wednesday-Thursday forecast of the storm off the Pacific Northwest coast has improved considerably over the past day, with trends among dynamical/machine learning (ML) models leaning deeper. Meanwhile solutions have recently been trending toward an intermediate idea for the upper trough reaching the West Coast (ECMWF cluster trending weaker and/or slower, GFS trending a little deeper). However model/ensemble solutions still diverge considerably from Friday through the weekend as the upper trough energy from this system continues through the western/central U.S. Potential arrival of upstream shortwave energy further complicates the forecast. Overall, ML models do not support a pronounced closed upper low late in the period, which especially questions the 00Z CMC run, while the suggest the primary surface wave reaching a position between the Upper Midwest and Great Lakes by next Sunday. This is similar to the dynamical ensemble means. There are a lot of different ideas for how low pressure could evolve offshore the West Coast by next Sunday, with no discernible clustering in dynamical or ML guidance, thus favoring a conservative depiction for now. Over the East, preference remains with the majority ECMWF cluster for the weak wave departing from the Mid-Atlantic coast on Wednesday. The previously slow CMC has joined this group while the GFS is on the fast side. Then by next weekend guidance shows spread with a front that reaches into the Mid-Atlantic, likely with a pronounced temperature gradient. At the very least, ML models offer less support for the northern side of the spread. The updated forecast continued to employ a model composite early with 40 percent 12Z ECMWF and the rest split among the GFS/UKMET/CMC, followed by a rapid increase of 18Z GEFS and 12Z ECens/CMCens input while phasing out the GFS/CMC, yielding 75 percent means and 25 percent ECMWF by next Sunday. ...Weather/Hazards Highlights... From Wednesday into Thursday night the most prominent heavy rainfall focus should be over portions of Texas by Thursday as moist southeasterly low level flow from the Gulf interacts with an upper shortwave crossing northern Mexico. Some activity may initiate in the Day 4 period near the Rio Grande Valley but the signal is diffuse enough not to merit any risk area in the Excessive Rainfall Outlook. By Day 5 there is a much stronger signal, though with typical spread for where the best focus will be. Overall the best overlap of dynamical and ML guidance exists over southern Texas. The Day 5 ERO starts out with a broader Marginal Risk area, with no embedded Slight Risk depicted yet due to initially dry ground conditions and existing guidance spread. Improved clustering for location and amounts in the heavier part of the envelope could eventually merit an upgrade. Elsewhere, consensus amounts along the Pacific Northwest coast in association with the Wednesday-Thursday system have generally decreased somewhat from 24 hours ago, while the signal for a potential band of enhanced rainfall over the Mid Mississippi Valley ahead of a warm front is too diffuse to warrant a risk area yet on Day 5. Precipitation will spread across northern and central parts of the West late this week, with Plains low pressure and its trailing front eventually pushing the Texas rainfall eastward while spreading a broader shield of moisture across the central and east- central U.S. Some wintry weather will be possible over far northern latitudes but otherwise most precipitation should be in the form of rain. How much snow falls over the northern Plains next weekend will depend on how strongly the Plains/Upper Midwest system develops, with low confidence in specifics at this time. The next Pacific system may increase precipitation along the West Coast by next Sunday. The weak wave forecast to track off the Mid-Atlantic/New England coast on Wednesday may produce some light precipitation early but most likely just near the coast. The strong upper ridge over the West into Wednesday will bring well above normal temperatures to the region, with a broad area of highs 10-20F above normal with locally higher anomalies. There will also be potential for numerous daily records for highs/warm lows, especially during Wednesday. As the upper ridge shifts eastward with time, the West will cool down while already above normal anomalies over the central U.S. will increase. Locations from the northern-central Plains into Midwest should see one or two days of highs reaching 20-25F or so above normal by Thursday-Friday, with best potential for some daily records over the central High Plains on Thursday. The East will see near to slightly below normal temperatures Wednesday-Thursday and then increasing coverage of highs 10-20F above normal Friday into the weekend. However a front reaching the Northeast/Mid-Atlantic may define a sharp gradient between this warmth and cooler readings just to the north. 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