Extended Forecast Discussion NWS Weather Prediction Center College Park MD 307 PM EST Tue Jan 25 2022 Valid 12Z Fri Jan 28 2022 - 12Z Tue Feb 01 2022 ...Coastal winter storm threat from the Mid-Atlantic to especially New England Friday into the weekend... ...Overview... At the beginning of the medium range period late this week, deep troughing will traverse the eastern half of the U.S. and spin up a significant and rapidly deepening surface low in the western Atlantic. This strong coastal storm may cause heavy snow in the coastal Mid-Atlantic region with more certainty for heavy snow over the Northeast, where high winds and coastal flooding are also likely through the weekend. Meanwhile, initial ridging in the West will be somewhat disrupted by Pacific energy tracking eastward over the weekend, before a more potent trough digs into the West early in the workweek and finally flips the overall upper pattern somewhat with decreasing heights over the West and rising heights over the East. ...Guidance Evaluation/Predictability Assessment... Recent guidance is still on track with a significant low pressure system in the western Atlantic late this week, though with some bouncing around in the exact placement of the low and its track. Sources of this uncertainty include several upstream shortwaves (a couple moving through the Great Lakes region and one diving approximately through the Rockies Wednesday night-Thursday night) that affect the development of the upper-level trough. These fine-scale features will still take a while to be resolved satisfactorily. In general, 00Z/06Z guidance showed a slightly eastern track compared to the previous runs, but with the exception of the deterministic ECMWF and to a lesser extent the EC mean on the western side. Cluster analysis and plots of individual ensemble lows showed that the EC suite of guidance was pretty consistently farther west as the low develops than the deterministic GFS runs and GEFS and CMC ensemble members, given an EC wider trough bumping up to a bit more of an upstream ridge in the Atlantic so a low wraps in. However, then the 12Z GFS, GEFS mean, and CMC came in with a slight westward shift in the low track, though not quite as far west as the 00Z and new 12Z ECMWF. So, the strategy of taking a middle ground position with the low between the western/eastern extremes seems to have worked well, and this was similar to the previous forecast position of the low. This forecast track also shows more snow as the dominant precipitation type rather than sleet/freezing rain. Models agree regarding ridging in the West initially on Friday, with a compact possibly closed low in the eastern Pacific. This relatively small feature could still lead to predictability issues for a while as it tracks eastward into the Southwest this weekend and with less certainty beyond then. The GFS runs and ECMWF start out in good agreement while the 00Z CMC did not cluster well with consensus (the 12Z run looks better). By early next week, GFS runs kept stronger energy farther north compared to a weakening EC feature in South Texas early Monday. The larger scale upper trough eventually reaching into the western U.S. will be from some combination of progressive North Pacific energy and flow descending from Alaska. Differences by day 7/Tuesday are within the realm of typical guidance spread/error at that time frame but differences remain in its evolution. The WPC forecast early in the period used a blend favoring the GFS and ECMWF runs as well as continuity, with an Atlantic low position generally in between the deterministic guidance and some manual enhancement in terms of the central pressure. Increased the proportion of ensemble means by the end of the period to resolve some of the timing and detail differences that arise. ...Weather Highlights/Threats... Key Messages for January 28-30 (Friday-Weekend) Winter Storm: Confidence is increasing that a significant winter storm will create considerable impacts Friday through the weekend from the Mid-Atlantic through the Northeast. Heavy snow is most likely in parts of New England. Heavy snow is still possible further south on the East Coast, including the major I-95 metropolitan areas from New York City to Washington D.C., but that is more uncertain at this time. Significant coastal impacts are possible in the Northeast, including coastal flooding and beach erosion. Additionally, strong winds may cause blowing snow and some damage. Hazardous travel conditions are likely in parts of the region. Please continue to monitor for updates, and check your local forecast at weather.gov. Other Weather Highlights: Currently it appears that the upper trough/low that may track into California and the Southwest this weekend could be weak enough not to produce much if any precipitation over that region. Its strength and track thereafter will determine how much precipitation may develop from the Gulf Coast northward by the first part of next week. Confidence is very low given a wide array of possibilities between meaningful amounts and dry conditions. Ahead of the northeastern Pacific upper trough, moisture should begin to move into the Northwest on Sunday and then continue to spread across more of the West with time. Highest totals of rain/mountain snow should be over the Pacific Northwest, but amounts do not appear too significant at this time. A series of waves/fronts may bring episodes of light and scattered snow into parts of the Great Lakes. Much of the eastern half of the country will be quite chilly through the weekend, with Saturday-Sunday having the broadest coverage of temperatures 10-20F below normal. Expect a warming trend to bring readings back close to normal by Monday or Tuesday. Much of the Plains will see above normal temperatures (up to plus 10-20F anomalies) late this week into Monday, aside from a cool Friday over far southern areas. Northern locations will see a colder trend Monday-Tuesday while the relative warmth farther south spreads a bit farther eastward. The West should see plus 5-10F or so anomalies through the weekend followed by a cooler trend early next week as upper troughing moves in. Tate/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 Hazards: - Heavy snow across portions of the Central Appalachians, Fri, Jan 28. - Heavy snow across portions of the Mid-Atlantic and the Northeast, Sat-Sun, Jan 29-Jan 30. - High winds across portions of the Southeast, the Mid-Atlantic, and the Northeast, Sat-Sun, Jan 29-Jan 30. - Much below normal temperatures across portions of the Mid-Atlantic, the Lower Mississippi Valley, the Central/Southern Appalachians, the Tennessee Valley, the Northeast, the Southeast, the Great Lakes, and the Ohio Valley, Sat-Sun, Jan 29-Jan 30. - Much below normal temperatures across portions of the Upper/Middle Mississippi Valley, and the Great Lakes, Fri-Sat, Jan 28-Jan 29. - High significant wave heights for coastal portions of the Mid-Atlantic and the Northeast, Sat, Jan 29. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml