Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Mon Jan 24 2022 Valid 12Z Thu Jan 27 2022 - 12Z Mon Jan 31 2022 ...Overview... Latest guidance continues to show a mean upper level pattern that features troughing over the East, varying degrees of ridging over the West, and a developing northeastern Pacific trough that may approach the West Coast early next week. Within this fairly agreeable regime there are still significant uncertainties regarding specifics of an eastern U.S. amplified trough that will likely support a western Atlantic storm Friday into the weekend with some effects possible over New England in particular, as well as for a shortwave approaching the West Coast late this week. Issues near the West Coast may have some influence on the forecast farther to the east. There are also differences with details of the late-period northeastern Pacific trough, affecting how much moisture reaches the Northwest. Between these areas of contention, a series of weak systems may bring light precipitation to some areas from the northern tier into the Appalachians. The forecast temperature pattern remains similar with the East generally below normal through the weekend and the West into portions of the Plains above normal for most days. ...Guidance Evaluation/Predictability Assessment... Even though the large scale mean pattern has been rather consistent in the guidance, the embedded areas of uncertainty involve aspects that are smaller in scale and lead to lower predictability. Over recent days, most operational models have been varying with the exact depiction of shortwave energy within the amplified upper trough that heads into the East and supports Atlantic cyclogenesis late week into the weekend--thus leading to important differences in track/timing/strength of the surface system. One positive trend is a deeper depiction in the ensemble means compared to previous days, suggesting that member spread may be decreasing somewhat. However there is still enough track variance among the guidance to result in a wide variety of potential effects, especially over New England and to a lesser extent farther south. On one hand the recent CMC runs and associated ensembles have tended to be on the northern/northwestern side of the full guidance spread and the new 00Z run actually brings the track into New England. On the other extreme the 12Z ECMWF was so far east that it brought hardly any precipitation at all to New England. Remaining solutions are between these extremes with the consensus trend among 12Z/18Z and new 00Z guidance appearing to be somewhat westward. An intermediate approach provides the best stability for the time being. A major change in the new 00Z ECMWF highlights the sensitivity of the forecast, as it now shows a very deep low just off New England by late Saturday--a little north of a similarly wound-up UKMET. Guidance also continues to have difficulty with the details of shortwave energy approaching the West Coast late this week and then filtering through the western mean ridge. Latest GFS/UKMET/CMC runs have been suggesting the potential for an upper low to close off while recent ECMWF runs and the ensemble means have kept it as an open wave. The new 12Z ECMWF has trended more to the other models in principle. These differences first affect the coverage and amounts of precipitation near the West Coast. Then the varied handling of this energy leads to various ideas for how much precipitation may develop over the southern Plains/western half of the Gulf Coast late in the period. For the purposes of a single deterministic forecast, prefer to maintain the open wave depiction for better continuity but with fairly low confidence. Elsewhere, there is decent model/mean consensus for the developing northeastern Pacific trough but its evolution has some complexity involving multiple features, so details may take a while to resolve better. This favors a model/mean blend for the time being. An initial front should be dropping into the northern tier by Thursday followed by a wave tracking from the northern Plains through the Midwest and Great Lakes Saturday-Monday. Spread and run-to-run variability have been fairly typical thus far, with some gradual detail adjustments in consecutive consensus blends. The updated forecast started with a blend of 12Z/18Z model runs early in the period and then started to incorporate 18Z GEFS/12Z ECMWF means by day 5 Saturday, reaching 50 percent total weight by days 6-7 Sunday-Monday. ...Weather Highlights/Threats... Continue to monitor forecasts for the likely Atlantic storm development late this week and weekend. Recent trends are increasing the potential that New England could see meaningful precipitation and wind effects from this system. With lesser magnitudes of each, there is also uncertainty for what portions of the Mid-Atlantic may experience. Typical guidance errors for such systems at this time frame still allow for significant changes to the current forecast. It is hoped that arrival of some of the supporting dynamics into western Canada by Tuesday may start to provide improved refinement to the forecast around then or shortly thereafter. Before this storm develops, locations across the far southern tier may see some mostly light precipitation. Some locations near the West Coast may see an increase in precipitation with an approaching shortwave/possible compact upper low late week into the weekend but with low confidence in details. This energy could eventually support some precipitation over the southern Plains/western half of the Gulf Coast early next week. Flow ahead of a northeastern Pacific upper trough should bring rain and mountain snow into the Northwest but again with low confidence for timing and amounts. A wavy frontal system should bring mostly light snow to the Great Lakes and Appalachians late this week. One or more trailing weak waves may also produce scattered light snow over areas from the extreme northern tier into the Great Lakes. On Thursday northern parts of the East will see lows 10-20F below normal and locations near the East Coast will see highs 10F or more below normal. Reinforcing cold air reaching the east-central U.S. Friday will bring a broad area of temperatures at least 10-15F below normal over the East by Saturday. Most areas should rebound toward more normal readings by next Monday. Much of the West should continue to see moderately above normal temperatures (locally plus 10-15F anomalies) while the northern and central Plains will likely see one or more days with temperatures 10-20F above normal (especially Friday-Saturday). Lesser warmth may extend 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