Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM 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 impacts 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... Model guidance for the most recent couple of cycles continues to show a rapidly deepening (bomb) cyclone in the western Atlantic over the weekend, but continues to waffle somewhat with its exact track, and the relatively fine-scale wobbles can cause notably different weather impacts. 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. ECMWF runs have been reasonably persistent on the earlier/deeper side with GFS runs at little later/weaker. Overall the forecast position for the low on Saturday and Sunday was very similar to the previous WPC forecast issuance, per the 00Z/06Z model consensus and taking somewhat of an average position between the slightly slower EC other faster models. However, incoming 12Z guidance has shown a slightly eastward/more offshore trend particularly on Saturday. Models continue to improve their agreement with the small upper trough/low moving from the Pacific into the Southwest over the weekend and the Southern Plains early Monday before weakening as it heads into a developing mean ridge in the East. However, more model differences arise with the deeper upstream troughing expected to dig during the first half of next week in the West. The general trend in the 00Z/06Z model guidance was a slightly faster trough axis moving eastward especially by Tuesday-Wednesday, which pushed the cold front ahead of it faster than the previous forecast. There is still considerable uncertainty with the multiple pieces of energy serving to create/dig this trough, which mainly stem from high latitude/Pacific regions with low predictability. Of the 00Z model cycle, the CMC showed some stream separation producing a southern stream low diving off the coast of California Monday-Tuesday unlike other guidance. This appeared to be somewhat of an outlier based on consensus and most individual ensemble members, but the new 12Z GFS ended up looking quite similar to that 00Z CMC, while the 12Z CMC ended up without this pattern, closing off a southern stream low well west in the Pacific as did the incoming 12Z ECMWF. This is just an indication that though model guidance may indicate agreement at times, there is still low confidence in the details, and the forecast still may go through changes with the trough axis and frontal timing. A multi-model deterministic blend was used early in the medium range forecast period, with the 00Z/06Z GFS runs and the 00Z ECMWF, CMC, and UKMET. Gradually increased the incorporation of the GEFS and EC ensemble means to about half by the end of the period given increasing model differences and uncertainty. ...Weather Highlights/Threats... To start the period Saturday, heavy snow is likely across the Northeast with possibly some snow lingering in the coastal Mid-Atlantic region. Latest forecasts show the highest confidence in heavy snow amounts likely near coastal New England. 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. See the WPC website for updated Key Messages on the system and check your local forecast at weather.gov. 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 in the south-central U.S. 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 average readings over Texas and vicinity, much of the Plains will see above average temperatures from the weekend into next week with readings up to 10-20F or so above normal, locally higher. 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 average 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. 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 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