Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Wed Mar 26 2025 Valid 12Z Sat Mar 29 2025 - 12Z Wed Apr 02 2025 ...Overview... Continue to expect a moderately progressive pattern with active weather across portions of the Lower 48. A southern stream shortwave should bring a threat of locally heavy rain into the east-central Gulf Coast early this weekend, but with less extreme totals than expected farther west in the short range time frame. Meanwhile emerging western dynamics will help to develop a wavy frontal system pushing eastward from the Plains through the East this weekend into next Monday. This system should produce some wintry weather over northern latitudes with areas of enhanced rainfall farther south. A system most likely to track northward offshore the West coast should spread precipitation into the West from late weekend into early next week. Additional precipitation may reach the West into midweek, while leading moisture reaches the east-central states, but guidance shows a lot of spread for flow details by then so forecast confidence trends well below average. Very warm temperatures will prevail ahead of the Plains/eastern U.S. system while trailing cooler air will bring readings back down to near or below normal. ...Guidance/Predictability Assessment... Models are still working on resolving important finer details of shortwave energy emerging from the West during the weekend and continuing eastward thereafter. Shortwave differences have a meaningful impact on surface wave specifics, with dynamical and machine learning (ML) models still exhibiting a fairly wide envelope by the time the system reaches the East. Among the 12Z/18Z guidance, GFS runs and the UKMET were on the sharp/strong side with the shortwave and the CMC on the weak/broad side. Ultimately preferred a blend of the 18Z GFS/12Z ECMWF and their ensemble means early in the period, trending to just 30 percent ECMWF and the rest means by Day 5/Monday. Farther west, guidance has also been quite diverse for low pressure that may develop close to the West Coast around Sunday- Monday. Some solutions like the 12Z CMC/UKMET merely brought a weak wave into California while other solutions wrap it northward into the mean low off the Pacific Northwest. ML models varied a lot as well, thus providing little additional insight. The aforementioned preference maintained good continuity with offshore development lifting into the northern mean low. Behind this system there is still remarkably wide divergence for aspects of the blocky pattern over the Pacific and extending into the Lower 48, with areas over the eastern Pacific and western U.S. in particular showing ensemble members ranging between a ridge and a trough--the GFS/GEFS tending to have more troughing over the eastern Pacific and the ECMWF/CMC favoring a deeper trough over the West. Adding to the confusion, some ML models actually develop a decent ridge over the West while the AIFS tilts in the operational ECMWF direction. Even with the differences aloft, by Wednesday there is at least a common surface theme of high pressure over the East and an axis of lower pressures over the Plains. At that time favor a conservative forecast combining the GEFS/ECens means to yield flat to broadly cyclonic flow aloft while waiting better agreement in the dynamical and ML models. ...Weather/Hazards Highlights... The Day 4/Saturday Excessive Rainfall Outlook maintains a Marginal Risk area along and somewhat north of the central/east-central Gulf Coast region, with only minor adjustments from continuity. Guidance is consistent with the setup for locally heavy rainfall (but trending somewhat lighter than across areas farther to the west), as the supporting southern tier upper shortwave pushes eastward. The distribution of solutions has remained similar as well, with the ECMWF/UKMET and machine learning models clustered in showing meaningful rainfall potential given sufficient moisture and instability versus a more diffuse signal in other guidance. By Day 5/Sunday expect a broad area of convection to develop over the east-central U.S. ahead of the wavy front pushing eastward from the Plains. Current guidance recommends a broad Marginal Risk area from the Ohio Valley southwest into parts of the lower Mississippi Valley. Improved guidance clustering especially from the Ohio Valley southward where soils are on the damp side could eventually lead to an embedded upgrade in risk level. More broadly, the wavy frontal system affecting the central and eastern U.S. will produce meaningful precipitation from the northern Rockies/High Plains into the Northeast as well farther south over the East, though the latter should be with lighter totals than forecast over the area covered by the aforementioned Day 5 Marginal Risk. In addition, the Storm Prediction Center is monitoring the potential for severe weather from the east-central U.S. to the Mid-Atlantic/Southeast during Sunday-Monday. Check latest SPC outlooks for the latest info on severe threats. Some snow will be possible across northern latitudes, with Rockies and Plains totals dependent on elevation and/or time of day. There may be a band of wintry mix separating the snow from rain from the Upper Midwest into New England. After a brief break, an area of rain and high elevation snow should reach into the West by Sunday-Monday, most likely from northern California into the Pacific Northwest and perhaps extending into the northern Rockies by early next week. There is still spread in the guidance for supporting low pressure but new solutions are starting to cluster somewhat better for low pressure wrapping up offshore the Pacific Northwest. Increasingly dramatic guidance differences for the eastern Pacific/western U.S. pattern early-mid week lead to low confidence for how much additional precipitation may reach the West Coast. Initially preferred ensemble-based guidance suggests a wetter trend focused along the central West Coast into midweek, but there is a minority of solutions with a drier forecast. Very warm temperatures will prevail in the warm sector ahead of the wavy frontal system evolving over the Plains and then pushing eastward. During the weekend expect the warmest anomalies to extend from the southern half of the Plains through the Midwest, Ohio Valley, and Mid-Atlantic with readings 10-25F above normal (with morning lows tending to be somewhat more anomalous than daytime highs). Frontal progression will confine the warmth more toward the East Coast by next Monday. Northern New England should remain a lot colder though, as a sharp front stays just to the south. Near to below normal readings will progress eastward behind the Plains/eastern U.S. front, with precipitation keeping some northern-central High Plains locations 10-15F below normal for highs during the weekend. Periods of unsettled weather will keep the diurnal spread over the West Coast states more narrow than usual. 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