Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Sat Feb 26 2022 Valid 12Z Tue Mar 01 2022 - 12Z Sat Mar 05 2022 ...Overview... Latest guidance continues to show an upper pattern consisting of a western ridge and broad eastern mean trough through midweek, followed by a transition toward a mean trough settling into the western U.S. while upper heights rise farther to the east. The primary precipitation focus early in the period will be over the Pacific Northwest and northern Rockies ahead of the eastern Pacific trough that eventually moves into the West. Progression of this trough later in the week into next weekend will spread precipitation over other parts of the West and then bring a variety of precipitation types to the central U.S. as low pressure emerges over the Plains. Ahead of this system, expect most precipitation east of the Rockies to be confined to a couple episodes of snow across northern areas with associated surface waves. The pattern evolution will favor above normal temperatures over a majority of the western/central U.S. through Wednesday or Thursday and then a cooler trend over the West and warmer readings over the East. ...Guidance Evaluation/Predictability Assessment... Two dominant uncertainties remain within what continues to be an agreeably depicted mean pattern evolution through the period. The first involves the east-west shortwave energy forecast to be over central Canada on Tuesday and then drop into the cyclonic flow downstream, with Tuesday-Thursday surface low pressure and frontal system very sensitive to the exact details of the energy aloft. The upper feature is south/southeast of a closed high and such a configuration tends to yield low predictability, with model/ensemble spread demonstrating this idea so far. In latest cycles the ECMWF/GFS have tended to be most sheared with the shortwave energy and thus weak with low pressure, while the UKMET/CMC's more concentrated depiction of energy aloft results in a stronger surface system. Ensemble means generally reflect the ideas of their parent models. For now the preference leans on the weaker side to maintain better continuity until there is reason to be more confident in the alternative. The second uncertainty involves the upper trough moving into the West by Thursday. There has been progress toward better agreement to some degree, as latest GFS runs have stabilized toward a fairly amplified trough that had been advertised by most other guidance. The CMC is still a little questionable as it is more amplified than most other solutions at some valid times and the new 00Z run has an extra embedded low within the trough as it comes ashore. The character of upstream small-scale energy dropping into the overall trough (00Z CMC an amplified extreme) still complicates the forecast. The 12Z ECMWF was reasonable for this feature but still strayed on the fast side with the central U.S. dynamics and surface system by next Saturday--due in part to being quicker to lift out eastern troughing. For the updated forecast, guidance comparisons led to an operational model emphasis early followed by partial incorporation of the 18Z GEFS/12Z ECMWF means. ECMWF input consisted of both the 12Z run and prior 00Z version through the period due to the older run having some appealing traits for both systems of interest. Two-thirds total weight of the GFS/ECMWF into early Thursday yielded the desired outcome for the eastern U.S. wave whose character remains a significant question mark. ...Weather Highlights/Threats... Moist flow ahead of the upper trough initially over the eastern Pacific should continue a Pacific Northwest atmospheric river event already in progress at the start of the period early Tuesday. Amounts during Tuesday-Wednesday should be somewhat lower than in the short range at the start of the week but could still be meaningful at some locations. Some of this moisture will extend into the northern Rockies. Progression of the upper trough into the West after midweek should lead to a lighter trend along the West Coast and spread precipitation into central California and some other parts of the West, mostly with light to moderate amounts of rain and higher elevation snow. Expect precipitation to expand across the central U.S. late week into the weekend as western trough energy reaches far enough east to support Plains low pressure. Best potential for some wintry weather will be over the northern third of the Plains into the Upper Midwest. Areas from the Upper Midwest into Northeast may see a couple periods of snow Tuesday-Thursday in association with clipper systems, the first one fairly well forecast but the second having much greater uncertainty for strength/track details. Thus confidence is a lot lower for coverage and amounts of snow with the second system. Above normal temperatures will prevail over a majority of the western and central U.S. Tuesday-Wednesday. Progression of the initial eastern Pacific upper trough will promote a cooler trend over the West after midweek and then favor northward expansion of above normal temperatures (plus 10-15F or so anomalies) from the South across a greater portion of the eastern U.S. Plus 10-20F anomalies will be possible for max and/or min temperatures for one or more days over the Great Basin/Southwest through midweek and parts of the Rockies/Plains into later in the week. Central Plains locations could exceed plus 20F anomalies for highs. Areas from the Upper Midwest to the Northeast will tend to be moderately below normal and colder air filtering into Montana/North Dakota could bring highs down to 10-20F below normal by next Saturday. 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