Extended Forecast Discussion NWS Weather Prediction Center College Park MD 222 PM EST Wed Mar 02 2022 Valid 12Z Sat Mar 05 2022 - 12Z Wed Mar 09 2022 ...Heavy snow potential over the Northern Plains through Upper Great Lakes and possibly into northern New England during the weekend... ...Heavy rainfall potential from the Mid-Lower Mississippi Valley into Tennessee/Ohio Valleys late weekend into early next week... ...Overview... Guidance maintains the forecast of a positively tilted mean trough from Canada into the western U.S., between a strong ridge over the eastern Pacific and another ridge that meanders over or near the southeastern Gulf of Mexico. This configuration will support an active weather pattern, with a couple episodes of precipitation over parts of the West and likely one or more areas of significant rain and snow over some areas of the central and eastern U.S. The system having highest confidence will track northeastward from the central Rockies/Plains into the Upper Great Lakes this weekend with a corresponding band of snow from the north-central High Plains through the Upper Great Lakes and possibly northern New England. A trailing upper low reaching the West should ultimately produce another surface wave, along the first system's cold front, that takes a somewhat farther southeast track but whose details are otherwise less certain. This evolution may support an area of heavy rainfall over parts of the east-central U.S. late weekend into early next week and possibly some wintry weather on the cold side of the second wave. Below normal temperatures initially over the West and northern Plains will expand into the rest of the central U.S. while frontal progression will gradually trim the western extent of much above normal temperature anomalies over the central/eastern states. ...Guidance Evaluation/Predictability Assessment... After some significant variability and spread in recent days, guidance over the past day appears to be stabilizing within the stronger half of the prior envelope for strength as the initial surface low and shortwave reach the Upper Great Lakes early Sunday while maintaining decent continuity for track, with just a bit of east/west spread. Consensus continues to show better definition of the initial low as it continues northeastward into the Canadian Maritimes by Sunday morning, along with a slight shift of the shortwave and cold front southward overall compared to the previous cycle. The pattern remains complex behind the leading wave, as a likely closed upper low in the West over the weekend ejects east early in the workweek, but is muddled by shortwave energy dropping into the West immediately behind it and also separate upper troughing that drops into the northern Plains and vicinity. While a cold front is likely ahead of the mean trough, guidance continues to waffle with placement of waves of low pressure along it. The 00Z ECMWF and 06Z GEFS means showed a position for the low near the Indiana/Ohio border early Monday, with more variability in position among deterministic models, but the newer 12Z models have started to cluster better approximately in that location. Then upstream, there are ample differences in the details of the pattern by Tuesday-Wednesday given multiple interacting low predictability shortwaves. The ECMWF and CMC have been persistent in holding troughing back across the Southwest in a very positively tilted form, while GFS runs have showed more progressive troughing. The 00Z EC/CMC pattern is almost outside the envelope of ensemble members with this Southwest trough. Thus somewhat preferred the GFS solutions along with the "middle ground" EC mean. Newer 12Z guidance shows a faster trough in the EC/CMC and slower in the GFS, so perhaps a consensus is being reached, at least temporarily. Early in the period a blend of the 00Z/06Z operational GFS, ECMWF, and CMC models provided a reasonable starting point for the forecast. The 00Z UKMET was an outlier with portions of the pattern, with a slightly eastern track of the main closed upper low in the West compared to consensus, but more so with much stronger upstream energy coming into western Canada and suppressing the eastern Pacific ridge by Monday. The ensemble means did have a hint of this, and the 00Z GFS was most like them, but not to the extreme of the UKMET. The UKMET seemed reasonable across the East though. Then as the period progressed, introduced and increased weighting of the ensemble means, particularly the EC mean that showed a deeper trough in the Southwest but not to the extreme of the operational EC and CMC. ...Weather Highlights/Threats... Across the West, the leading system emerging into the Plains may produce some central Rockies snow early in the weekend while the system immediately behind it spreads rain and higher elevation snow primarily from the Sierra Nevada into the Wasatch and central Rockies. Expect generally light to moderate totals but with some locally heavier totals possible. There is continued potential for another system to spread mostly light to moderate precipitation into the Northwest/northern Rockies during the first half of next week but with less than ideal confidence in the details. To the east of the Rockies, the leading system forecast to track from the central Plains through Upper Great Lakes during the weekend should spread wintry precipitation from the north-central High Plains into the Upper Great Lakes and eventually New England (where a changeover to rain may occur). Highest probability of significant snowfall remains just to the northwest of the surface low track, with increasing chances over the northern Plains and continued chances over the Upper Midwest. The storm may be strong enough to produce some brisk winds, with specifics to be resolved in coming days. Rainfall of varying intensity will be possible over the rest of the central/east-central U.S. ahead of the trailing cold front. Embedded thunderstorms could be severe in the Mid-Mississippi Valley on Saturday and the Lower Mississippi Valley on Sunday per the latest Storm Prediction Center extended outlook. Guidance is still showing potential for heavier rainfall within an area from the southeastern Plains into the Ohio/Tennessee Valleys by Saturday night/Sunday into early next week, and there is a Slight Risk of excessive rainfall in place in WPC's newly experimental Day 5 outlook. This threat corresponds to slower progression of the trailing front as it becomes more aligned with flow aloft, interaction with low level Gulf moisture, and the possibility of one or more waves that would provide added rainfall focus. The northwestern fringe of this moisture shield should contain some wintry weather, likely along an axis somewhat southeast of the first episode. Specifics will depend on lower-confidence wave details which will take additional time to resolve. One change with this forecast cycle was model guidance taking the bulk of the rainfall eastward rather than southward as the cold front progresses, so trended down with QPF over the Gulf Coast states, but this is still subject to change. Colder air initially over the western U.S. and northern Plains and spreading over the rest of the central U.S. into early next week should yield a broad area of temperatures that are 5-15F below normal. Best potential for locally colder anomalies, especially for highs, will be over the northern/central High Plains. Leading warm sector air, initially focused over the central-southern Plains and southern two-thirds of the East on Saturday, will become more pronounced over the East by Sunday-Monday when plus 10-25F above normal anomalies for highs and localized higher anomalies for morning lows may challenge daily records for highs/warm lows. Highest concentration of record highs may be over the Southeast with a few record highs elsewhere, such as the Mid-Atlantic. Coverage of record warm lows may be broader. After Monday, frontal progression will increasingly confine the warmth to the Southeast, with record warmth remaining possible in Florida. 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