Extended Forecast Discussion NWS Weather Prediction Center College Park MD 155 PM EST Wed Feb 19 2025 Valid 12Z Sat Feb 22 2025 - 12Z Wed Feb 26 2025 ...Wet Pacific Northwest pattern this weekend/early next week... ...Overview and Guidance/Predictability Assessment... The latest models and ensembles still show a reasonably similar larger scale flow evolution over the next week, albeit laden with numerous smaller scale embedded system differences that often do not have good cycle to cycle continuity. Moderate progression of these individual shortwaves aloft in split streams over the lower 48 this week is still likely to evolve toward a larger scale mean upper pattern highlighted by a western ridge and eastern trough positions by the start of next week. This transition will bring the best potential for meaningful precipitation to the Pacific Northwest from the weekend into early next week, along with a pronounced warming trend from west to east over the lower 48. The 00Z/06Z guidance available for this forecast update along with incoming 12Z data show some detail refinements early in the period and then maintain recent spread for other embedded features. Most solutions now show more separation between Midwest and southern Rockies shortwave energy as of early Saturday. This trend for the southern shortwave has increased rainfall potential over parts of the Gulf Coast states. GFS runs are a bit extreme on the depth though. There is fair agreement in concept with a southern Canada/Great Lakes-New England system early-mid week as shortwave energy crosses the region, but spread persists for timing with no prominent cluster emerging yet. For the fairly vigorous system reaching the Pacific Northwest/Vancouver Island early next week, latest machine learning (ML) models join most other guidance in suggesting faster progression than latest GFS runs by next Tuesday. The upper shortwave should support Plains/Midwest low pressure by Wednesday, with the GFS still leaning on the slow side. ML models hint at the potential for a more amplified shortwave than the dynamical model average, along with a surface pattern closest to ECMWF runs and the ensemble means (especially the better defined GEFS/CMCens). New 12Z dynamical models generally support the ML model ideas of slightly lower pressures with the surface system than what most 00Z/06Z models/means were offering. A composite of 00Z/06Z operational models provided a reasonable starting point early-mid period, reflecting latest detail trends or a reasonable intermediate solution depending on the feature. After Monday the forecast transitioned toward phasing out the 00Z/06Z GFS and then the 00Z CMC, in favor of the past two ECMWF runs (00Z and prior 12Z/18 cycles) and increasing 06Z GEFS/00Z ECens/00Z CMCens input. ...Weather/Hazards Highlights... An impressive Arctic airmass has settled over the central and eastern U.S., but will steadily warm through the weekend into next week. Saturday will still be cold over parts of the central/eastern U.S., and especially southern Texas where highs could be 20-30 degrees below normal. Above average temperatures will develop over the West and eventually the central U.S. where by early next week most locations west of the Mississippi River will warm to above normal with decent coverage of plus 10-25 degree anomalies. Best potential for highest anomalies will be over and near the northern Plains. Temperatures over the East should reach near to above normal by the early-middle part of next week. Guidance continues to offer a strong signal for a pattern favoring a longer fetch moisture feed to fuel rounds of moderate to heavy lower elevation rain and high elevation/mountain snow into the Pacific Northwest from Saturday into early next week. Enhanced snows will work inland over the northern Intermountain West/Rockies. The best potential for highest precipitation totals exists over the favored terrain and coastal areas of western Washington/Oregon and into northwest California. The Days 4/5 WPC Excessive Rainfall Outlook (ERO) both show a similar focused Marginal Risk area, with minimal change in this afternoon's update. The Northwest should trend drier by midweek as a Monday- Tuesday system departs and upper ridging builds in. Farther east, strongly organized storm systems generally appear unlikely over the central to eastern U.S. despite multiple uncertain impulses riding into the eroding Arctic airmass and with flow transition. A medium to smaller scale shortwave ejecting from the southern Rockies during the weekend may support periodic moderate rainfall over the Gulf and possibly inland into the Gulf Coast states to the north of slow moving and wavy frontal zones. Recent trends have been heavier with this activity but so far the models are keeping instability over the Gulf. Thus the ERO continues to show no risk area for this region. Most precipitation should be rain, though a little wintry weather could be possible in the northern fringe of the moisture shield if it extends far enough north. Surface wave/frontal details over the Gulf into the western Atlantic are still somewhat murky from late weekend into early next work week. However features may evolve, any waves should be weak and most precipitation should stay offshore the Mid-Atlantic/New England coast. Digging of northern stream shortwave energy this weekend into early next week will spread light precipitation (mostly snow) from the Great Lakes region through New England. Latest guidance is not too enthusiastic about potential for wrapback coastal low linkage over the Northeast to enhance activity early-mid next week but it remains worth monitoring in future runs. Another system may develop over the Plains/Mississippi Valley around next Wednesday. The warmer pattern by then should favor mostly light to moderate rain aside from perhaps a little wintry weather on the cool side of the surface low. Rausch/Schichtel 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