Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Wed Jan 26 2022 Valid 12Z Sat Jan 29 2022 - 12Z Wed Feb 02 2022 ...Coastal winter storm threat from the Mid-Atlantic to especially New England Friday into the weekend... ...Overview... Early in the medium range period from Saturday into early Sunday, a deep upper trough reaching the East Coast will likely close off an embedded upper low that tracks near the New England coast. The evolution aloft will support further deepening of strong low pressure just off the East Coast and direct the system northward, from east of the Mid-Atlantic coast into the Canadian Maritimes. This strong coastal storm may cause heavy snow in the coastal Mid-Atlantic region with higher confidence for heavy snow over the Northeast, where high winds and coastal flooding are also likely through the weekend. At the same time a weak eastern Pacific trough/upper low will cut through the southern part of initial ridging over the West. From late weekend into next week a more potent upper trough will push into the West and steadily amplify, ultimately flipping the upper pattern as a ridge axis reaches the East Coast by Wednesday. This configuration should lead to a pronounced increase of precipitation over the central U.S. by the end of the forecast period. ...Guidance Evaluation/Predictability Assessment... Latest guidance continues to favor an intermediate/consensus approach for depicting the western Atlantic storm during the weekend. A significant key to the forecast of the surface low by late Saturday appears to be exactly when, where, and how deeply the upper low within the overall trough closes off. In general GFS runs have tended to be a little later/weaker with the upper low while the 12Z ECMWF is somewhat on the earlier/deeper side. The 12Z ECMWF scenario brings the surface track back to the west for a brief time, which a number of ECMWF ensembles have also been doing. The 00Z CMC has a less pronounced and farther north depiction of this idea. The new 00Z ECMWF has adjusted east with the surface low toward the longer-term consensus due to a slightly weaker upper low. This is a very fine-scale detail and the supporting energy is still over northwestern North America so it may take additional time to resolve specifics with reasonable satisfaction. For the upper trough moving into the West, the forecast of leading energy has become more uncertain in the new 00Z cycle as models show varying ways in which some of the energy in the shortwave may get pulled off to the southwest--leading to meaningful differences in amplitude as the remaining energy reaches the West Coast. On the other hand, guidance from the 12Z cycle onward seems to have come into better agreement for the pattern from the North Pacific through Alaska and Siberia. This has in turn helped to narrow the spread somewhat for the larger scale upper trough amplifying into the West during the first half of the week. Models are slowly improving their agreement with respect to the weak upper trough/low moving into the Southwest during the weekend and continuing along the southern tier before weakening as it heads into a developing mean ridge in the East. General trends by the time the feature reaches the Plains have been more in the direction of the southern ECMWF versus some earlier northern GFS runs. The updated forecast started with a blend of 12Z models, with minor manual enhancement of the western Atlantic storm. The 12Z GFS compared slightly better in concept to other guidance versus the 18Z run. Meanwhile the model blend accounted for the most common ideas for the arriving western trough as of the 12Z/18Z cycles. By later in the period an average of recent operational model runs has fairly good support from the GEFS/ECMWF means for the amplifying western trough, so even by days 6-7 Tuesday-Wednesday the forecast included only 30 percent total ensemble mean weight. ...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 farther south along 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: It still appears that the upper trough/low that may track into California and the Southwest this weekend may 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. Over the past day guidance has started to show some convergence toward the idea of at least some meaningful rainfall along and north of the western half of the Gulf Coast by Monday. Moisture ahead of a northeastern Pacific upper trough should begin to move into the Northwest on Sunday and then continue to spread across more of the West with time as the upper trough moves inland and amplifies. Highest totals of rain/mountain snow should be over the Pacific Northwest, but amounts do not appear too significant at this time. Toward midweek the western trough and leading surface front will interact with a healthy flow of Gulf moisture to produce a rapidly expanding area of precipitation, some of it potentially becoming moderate to heavy. Lighter wintry precipitation will be possible over northern latitudes. A series of waves/fronts may bring episodes of light and scattered snow into parts of the Great Lakes before the larger scale pattern changes. The eastern U.S. will be quite chilly through the weekend with broad coverage of temperatures 10-20F below normal, including subfreezing lows extending into portions of Florida. Areas from the Mississippi Valley to Appalachians should see a moderating trend from west to east. Aside from some below normal readings over Texas and vicinity, much of the Plains will see above normal temperatures from the weekend into next week with readings up to 10-20F or so above normal. This warmth will progress into the eastern half of the country early-mid week with the increase of Gulf moisture helping to raise min temperature anomalies in particular by Wednesday. Moderately above normal temperatures over the West during the weekend will trend lower next week with the arrival of an amplifying upper trough and 5-15F below normal highs may extend from the Interior West into the High Plains/northern tier by Tuesday-Wednesday. Rausch/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, 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