Extended Forecast Discussion NWS Weather Prediction Center College Park MD 127 PM EST Sun Jan 23 2022 Valid 12Z Wed Jan 26 2022 - 12Z Sun Jan 30 2022 18Z Update: The 12Z model guidance suite is in above average agreement through next week on the overall synoptic scale pattern. At the time of product issuance, the 00Z UKMET differed across British Columbia and the Pacific Northwest by Wednesday with placement of the upper ridge axis by late Thursday. The 12Z GFS is a bit more amplified with the trough digging southward across the southern Plains for the middle-end of the week, but it fits the overall pattern and has ensemble support. Overall, the past few runs of the GFS have depicted a much more realistic scenario across the East Coast region for next weekend, compared to yesterday's 18Z GFS that had a massive blizzard hammering the East Coast region. The WPC forecast and model consensus supports the idea of a strong surface low developing well offshore on Saturday and then lifting northeastward towards Newfoundland, but it appears the majority of the high winds and heavy precipitation should remain offshore. There is still plenty of time to monitor future trends with this storm system. A multi-deterministic blend was incorporated for the WPC forecast for most of the forecast period, with some contributions from the GEFS and ECENS means for next weekend. The previous forecast discussion is appended below for reference. /Hamrick ...Overview... Models and ensemble means generally agree upon the idea of broad mean troughing aloft over much of the lower 48 as of Wednesday transitioning more to the eastern half of the country as a mean ridge over the eastern Pacific moves into the western U.S. Best consensus of guidance has a Pacific shortwave briefly suppressing the western ridge around Saturday followed by a rebound of the ridge, ahead of troughing over the far northeastern Pacific. The strongest system of the period will likely be low pressure expected to develop over the western Atlantic around the end of the week through the weekend, in response to a strong shortwave trough approaching and crossing the East Coast. Details remain too uncertain to resolve exactly what the system's effects will be over the East. Farther west, a couple clipper systems with fairly light precipitation will track over the northern tier while the late week/weekend pattern should bring at least a modest increase of moisture to the Northwest. For temperatures the East will be below normal most of the period while much of the West through portions of the Plains will be above normal. ...Guidance Evaluation/Predictability Assessment... Within the fairly agreeable mean pattern, the most prominent forecast uncertainties have been with the eastern Pacific/western U.S. evolution as shortwave energy approaches the upper ridge that reaches the West along with expected western Atlantic development as an amplified trough reaches the East late in the week. Model and ensemble spread remains considerable for the Pacific/West area, with recent GFS runs and 12Z CMC holding onto a stronger ridge versus the past couple ECMWF runs. However the 18Z and new 00Z GFS runs have adjusted much closer to the 12Z ECMWF and the ensemble means. The 00Z CMC has also trended toward this improving cluster. This leaves the 00Z UKMET that diverges from most other guidance for various aspects of the eastern Pacific/northwestern North American pattern. Perhaps with the aid of this better western agreement, the 00Z models have trended somewhat closer for the late week/weekend Atlantic development. In particular the 00Z GFS has gone away from the 12Z/18Z runs whose slower/sharper/elongated upper trough had produced a farther southwest storm than a great majority of GEFS/ECMWF/CMC ensemble members. The 00Z GFS/CMC and latest ensemble means are now similar in showing low pressure somewhat east of the Mid-Atlantic coast early Saturday and then tracking into or south of the Canadian Maritimes by early Sunday. The supporting shortwave energy is currently over the North Pacific and is not scheduled to round the East Pacific ridge until around Tuesday, plus guidance is still varying with the western ridge/Pacific energy heading into it, so it will likely take a while to gain much more confidence in a particular scenario. The forecast has been fairly consistent in concept for two fronts/waves expected to drop into the northern tier during the period, the first around Thursday and another during the weekend. There are still some typical detail differences and run-to-run adjustments that are best resolved by a blend approach. Models/means show better than average agreement for the upper troughing and surface system over the northeastern Pacific by the end of the period. An early period 12Z/18Z model blend trended toward 50-60 percent total weight of the 18Z GEFS/12Z ECMWF means by days 6-7 Saturday-Sunday to reflect the consistent and intermediate solution for Atlantic development in the means (minimizing 12Z/18Z GFS influence) and to account for ongoing uncertainty with details over the West late week into the weekend. ...Weather Highlights/Threats... A mid-late week wave/frontal system should spread an area of mostly light snow across parts of the northern Plains and Great Lakes/Northeast, followed by another system also accompanied by mostly light snow next weekend. The southern High Plains may see a little light precipitation Wednesday. Confidence is still not great for exactly how late week/weekend Atlantic storm development will affect areas near the East Coast. The most likely evolution would lead to some potential for snow and brisk to strong winds over New England with lesser probability for significant effects farther south. Typical guidance errors at this time frame still allow for significant changes to the current forecast. Approaching Pacific shortwave energy and then flow ahead of a developing northeastern Pacific upper trough may bring light to locally moderate rain and mountain snow into the Pacific Northwest during Friday-Sunday, with a little snow possibly extending into the northern Rockies. Within the chilly pattern over the eastern half of the country, coldest anomalies should extend from the Midwest/Upper Mississippi Valley through the Great Lakes Wednesday into early Thursday with readings 15-25F below normal and locally colder in parts of the Midwest early Wednesday. Somewhat less extreme cold anomalies will spread through the southern Plains/South and the East during that time. Reinforcing cold air should lead to decent coverage of 5-15F below normal temperatures over the East next weekend. Mostly above normal readings will prevail from the West through the northern half of the Plains. Some scattered plus 10-15F anomalies will be possible over and near the Great Basin and the northern Plains should have one or more days 10-20F above normal. Some of the positive anomalies should reach into the southern Plains by the weekend. 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