Extended Forecast Discussion NWS Weather Prediction Center College Park MD 152 AM EST Tue Jan 25 2022 Valid 12Z Fri Jan 28 2022 - 12Z Tue Feb 01 2022 ...Winter Coastal Storm Threat from the Mid-Atlantic to especially New England Friday into the Weekend... ...Overview... From late this week to the start of next week the models and ensembles continue to show an upper level pattern consisting of a mean trough over the East, varying degrees of ridging over the West, and a developing northeastern Pacific trough that should approach/reach the West Coast. Guidance expects the inland progression of the Pacific trough by Monday-Tuesday to flip the pattern somewhat, with decreasing heights over the West and rising heights over the East. Perhaps due in part from improving agreement for a lead Pacific shortwave/possible weak embedded low nearing California by Saturday, there is likewise narrowing spread of solutions for energy digging into an amplified U.S. trough that looks increasingly likely to support a significant and rapidly deepening western Atlantic coastal storm Friday into the weekend with effects from the Mid-Atlantic to New England in particular. Some differences persist for details of the upper trough moving into the West. ...Guidance Evaluation/Predictability Assessment... Emerging trends from yesterday along both coasts of the lower 48 during the late week/weekend time frame held up fairly well in the 12Z/18Z cycle of guidance. Slower and more separated evolution of the shortwave approaching California, likely yielding a weak upper low, allows for a more persistent upper ridge over the West and in turn somewhat stronger and slightly westward digging of shortwave energy (which is finally reaching northwestern North America today) into the East. Yet to be resolved is exactly when and where eastern energy closes off an upper low, with 12Z/18Z GFS runs doing so a bit later/northeastward than other models. In the new 00Z cycle the CMC has deviated significantly from other guidance over the eastern Pacific, leading to question marks in its forecast farther eastward--specifically a storm track a bit to the east of consensus versus multiple prior runs that were on the western side. Some important fine-scale details will still take a while to be resolved satisfactorily. A multi-model blend with some manual enhancement to maintain continuity in depth also provided reasonable consistency for a track just offshore New England. The relatively small and weak nature of the upper low that may track into the Southwest this weekend could still lead to predictability issues for a while. Trends over the past day have been slower, delaying the development of any potential precipitation along and north of the Gulf Coast. The new 00Z ECMWF has trended faster though. There is still a wide array of possible tracks after emerging from the Southwest early next week, with GFS runs tending to be the farthest north and thus driest. The 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 depend in part on whether there is a break in Pacific and Alaska/Siberia upper ridging (GFS/GEFS keep it connected, most other guidance shows a break), an issue that can ultimately lead to more significant differences over the lower 48. The aforementioned model blend used for the western Atlantic storm worked well elsewhere for the first half of the period as well. The forecast then transitioned toward half models/half means by late in 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. While uncertainty continues with the track and intensity of this system, it is becoming more likely that it will bring significant snow, sleet, and freezing rain to the region, including the I-95 metropolitan areas. Hazardous travel conditions are possible due to the combination of snow, sleet, freezing rain, and wind. Close to the immediate Atlantic coastline, strong winds combined with high astronomical tides may lead to coastal flooding. Please continue to monitor for future updates as this system develops. 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. 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. 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, 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