Extended Forecast Discussion NWS Weather Prediction Center College Park MD 204 PM EST Tue Feb 18 2025 Valid 12Z Fri Feb 21 2025 - 12Z Tue Feb 25 2025 ...Intense Central to Eastern U.S. Arctic Blast this week to moderate by the weekend... ...Wet Pacific Northwest pattern this weekend/early next week... ...Overview and Guidance/Predictability Assessment... Guidance continues to offer a reasonably similar larger scale flow evolution over the next week, albeit laden with numerous smaller scale embedded system differences. Moderate progression of these individual shortwaves aloft in split streams over the lower 48 this week is expected to lead an evolution toward a larger scale mean upper pattern highlighted by a western ridge and eastern trough 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 over especially the western-central U.S. in stark contrast to the ongoing Arctic airmass this week. A multi-model blend with some ensemble mean inclusion worked well for the start of the forecast period despite the smaller scale differences. As the period progressed, increased the proportion of ensemble means to over half the blend by Days 6-7. This maintained good continuity with the previous forecast, though a surface low coming across south-central Canada to the Great Lakes as a clipper system early next week has shown a little more clustering for a deeper low, despite continued spread. ...Weather/Hazards Highlights... Quite the impressive Arctic airmass is settling over the central and eastern U.S. this week. An Extreme Cold threat with widespread record temperatures for morning lows/cold daytime highs will linger into Friday over the south-central to southern U.S., but the broad airmass will continue to steadily moderate through the weekend into next week. Above normal 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 normal to slightly warmer into early next week. From Saturday onward the pattern becomes increasingly favorable for longer fetch moisture feed to fuel rounds of moderate to heavy lower elevation rain and high elevation/mountain snow primarily into the Pacific Northwest, but also inland to the northern Rockies. The best potential for highest totals currently exists over the favored terrain and coastal areas of western Washington and northwestern Oregon. A Day 5/Saturday WPC Excessive Rainfall Outlook (ERO) Marginal Risk area has been expanded eastward to western foothills of the Cascades due to the initially high snow levels at the start of a multi-day period of wet weather. Farther east, strongly organized storm systems generally do not look likely over the central to eastern U.S. despite multiple uncertain impulses riding into the eroding Arctic airmass and with flow transition. One feature to note is emerging western U.S. energy that may support periodic moderate rainfall over the Gulf and possibly extending into the Gulf Coast states in association with a persistent and slow moving wavy frontal zone. Most precipitation should be rain, but though a little wintry weather could be possible in the northern fringe of the moisture shield if it extends far enough north. Confidence is low regarding how the waviness may evolve over the Gulf during the weekend, and what the surface pattern may look like off the East Coast into early next week. The majority (though not all) of guidance still suggests most precipitation should stay offshore the Mid-Atlantic/New England coast. Meanwhile, a series of waves may spread light precipitation (mostly snow) across parts of the Great Lakes into New England from the weekend into early next week. Schichtel/Tate 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