Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Wed Mar 02 2022 Valid 12Z Sat Mar 05 2022 - 12Z Wed Mar 09 2022 ...Heavy snow potential over the Northern Plains through 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 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 snow 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... Early in the period a blend of the 12Z/18Z operational models provided a reasonable starting point for the forecast. 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 it reaches the Upper Great Lakes early Sunday while maintaining decent continuity for track. The 00Z CMC trended somewhat weaker than its 12Z run though. Latest consensus seems to be holding onto better definition as it continues northeastward. The trailing wave (or even two waves), initially supported by the next upper low tracking out of the West, still shows up in most guidance but it remains a complicated forecast. Not only does flow immediately upstream have some possible influence on the feature, but separate upper troughing that drops into the northern Plains and vicinity could eventually interact with it. Thus latest runs vary significantly for the character and timing of the surface reflection (new 00Z ECMWF trending notably slower for example), including differences in strength and whether there is one consolidated wave or possibly two waves. By early Monday the model blend and modest incorporation of the 18Z GEFS/12Z ECMWF means accounted for the uncertainty with this feature at that time. If anything, north-south spread has widened in the new 00Z guidance. Returning upstream later in the period, there is some relative agreement that mid-period energy over the West should gradually continue eastward (but with less effect on sensible weather) but a lot more spread with a shortwave expected to round the Pacific ridge and possibly drop into the Northwest. Ensemble means have tended to agree upon a somewhat faster progression than the latest ECMWF and especially CMC runs while the GFS and UKMET have been closer to the means in principle. For continuity the forecast ultimately trended a little more toward the ensemble means by next Wednesday with a little more weight to the GFS relative to the ECMWF for the lingering operational weight. ...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 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. 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. 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. Coverage of record warm lows may be broader. After Monday, frontal progression will increasingly confine the warmth to the Southeast. Rausch/Tate 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