Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Mon Mar 24 2025 Valid 12Z Thu Mar 27 2025 - 12Z Mon Mar 31 2025 ...Overview... Most guidance shows a reloading mean trough over the eastern Pacific with a strong system affecting the Pacific Northwest Thursday into Friday with potential for another meaningful system to affect the West Coast by Sunday-Monday. The downstream pattern looks moderately progressive, with a very warm Rockies/Plains ridge eventually moving off the East Coast while trailing shortwave energy supports low pressure that should track northeastward from the Plains during the weekend into early next week. The eastern Pacific systems will bring areas of enhanced precipitation to the West Coast while the system affecting the central/eastern U.S. by Saturday-Monday should spread a broad area of moisture east of the Rockies with some wintry weather possible over far northern latitudes. A southern stream shortwave crossing northern Mexico and Texas late this week may also produce some heavy rainfall along and inland from the western half of the Gulf Coast. ...Guidance/Predictability Assessment... Latest guidance agrees decently with the larger scale aspects over the overall pattern but there is still plenty of uncertainty for details of shortwave energy moving into the West late this week and continuing inland thereafter, affecting the forecast for low pressure that should ultimately track northeastward from the Plains. Trends over the past couple days have been leading toward an intermediate solution for the leading energy reaching the West while significant differences develop for the relative emphasis of leading energy versus trailing energy arriving from the Pacific. At least there is a somewhat coherent clustering of GFS/ECMWF runs and most ensemble means as the overall shortwave trough reaches the eastern half of the country, with surface low pressure near the eastern Great Lakes as of early next Monday. CMC runs had been too eager to close off an upper low but the new 00Z run seems to be tempering that tendency. Machine learning (ML) model spread is disconcerting though, with a couple suggesting potential for a faster leading wave and another one hanging back to the southwest, while another subset is closer to the model/ensemble majority. Off the West Coast, there is decent clustering for the strong system near the Pacific Northwest late this week though the new 00Z UKMET looks somewhat disjointed. There is still a lot of spread for specifics of the Sunday-Monday system but with the average of guidance trending somewhat stronger. ML models are still not developing this system too strongly though. Latest guidance comparisons based on 18Z/12Z guidance led to starting Day 3 Thursday with an operational model composite. The CMC was removed thereafter in favor of the CMCens mean, while the blend introduced some 18Z GEFS/12Z ECens after early Saturday. Day 7 Monday featured an even weight of models (18Z GFS/12Z ECMWF) and the means. ...Weather/Hazards Highlights... Guidance continues to show a late-week threat of locally heavy rainfall over parts of Texas and then extending eastward, as low level Gulf moisture and a warm front interact with an upper trough progressing across northern Mexico and Texas. There is still considerable spread for details, tempering confidence. The Day 4/Thursday Excessive Rainfall Outlook stays close to continuity in depicting a Marginal Risk area over central-southern Texas. Initially dry ground conditions and guidance spread continue to preclude an embedded Slight Risk area, though will continue to monitor trends for improved clustering on the heavier side of the envelope for any potential upgrade. As this activity likely drifts eastward, the Day 5/Friday ERO shows a Marginal Risk area along and somewhat inland from a majority of the Texas and Louisiana coast. This reflects the best overlap of guidance and is where heavier rainfall should be more likely based on instability. The Day 4 period maintains a couple regions of interest with no risk areas for now but require continued monitoring. Dynamical and machine learning guidance is very mixed regarding potential warm frontal rainfall over the Midwest. Meanwhile there has been a fair amount of spread and variability for rainfall along the Pacific Northwest coast. The best moisture reaches inland by Thursday but instability under the upper trough could lead to some enhanced rain rates. In addition to supporting Pacific Northwest precipitation, the strong storm offshore on Thursday may produce some strong winds near coastal areas. As the system's front and shortwave dynamics continue eastward, moderate amounts of rain and high elevation snow will progress across the northern half or so of the West late this week. Expect Low pressure developing over the Plains and tracking northeastward to spread an increasingly broad shield of precipitation across the central and eastern U.S. from the end of this week into next Monday. Some wintry weather will be possible over far northern latitudes but otherwise most precipitation should be in the form of rain, with some potentially on the heavy side. How much snow falls over the northern Plains during the weekend will depend on how strongly the system develops, with confidence in specifics remaining in the lower half of the spectrum. Another potentially vigorous eastern Pacific system may bring areas of enhanced precipitation to the West by Sunday-Monday. The strong upper ridge reaching the Rockies/Plains by Thursday will bring very warm temperatures to the region, with some areas over the Plains and eastern Rockies/Midwest seeing up to plus 20-30F anomalies for highs and/or morning lows during Thursday and/or Friday. Some daily records are possible over the High Plains. System progression will push a moderated form of this warmth farther eastward by the weekend, with plus 10-20F anomalies for highs. However a front settling into the Northeast/Mid-Atlantic may define a sharp gradient between the warm air and cooler readings just to the north. Behind the front anchored by the developing Plains low, near to slightly below normal highs will progress from the West through the central U.S., followed by a rebound over and near the Rockies by next Monday. 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