Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Tue Mar 01 2022 Valid 12Z Fri Mar 04 2022 - 12Z Tue Mar 08 2022 ...Heavy snow potential over the Upper Midwest/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... Models and ensemble means continue to show the establishment of a positively tilted mean trough aloft from Canada into the western U.S., between a building eastern Pacific ridge and another ridge that migrates across the Gulf of Mexico into the Bahamas. A leading impulse reaching the West by the start of the period early Friday and another feature arriving close behind will bring precipitation to portions of the West, followed by a broad area of precipitation to the east of the Rockies as two potential systems track into the Great Lakes/Ohio Valley. The first system should bring greater snowfall potential to the Upper Midwest/Upper Great Lakes and to some degree northern New England. Most guidance shows a second system developing along the trailing front whose slow movement due to alignment with southwesterly mean flow aloft late weekend into early next week could make it a focus for significant rainfall farther south. Below normal temperatures will settle over much of the western and central U.S. while much above normal readings from the central/southern Plains into the Southeast late this week become more pronounced over the East. ...Guidance Evaluation/Predictability Assessment... Within what continues to be a consistently agreeable pattern from a multi-day mean perspective, operational models continue to show some spread and variability for details and are still in the process of refining some of the specifics up to 5-6 days out in time. There are some common themes though. The period begins Friday with good consensus for three primary shortwaves within the broader western trough. The past few guidance cycles have indicated that the leading southeasternmost one centered over California Friday will likely be in the form of a compact closed low that crosses California and then ejects rapidly northeastward (with mixed signals for being open or closed at various valid times). The second shortwave now has better consensus that it will take the form of a closed low as it generally follows the track of the first, moving through the West and then turning northeastward. The third is most likely to track across southwestern Canada late this week and shear out early next week, though with its energy possibly combining with the initial shortwave as it reaches the Great Lakes. Then the 00Z CMC was alone in showing another small closed low diving south along the West Coast over the weekend, which was not favored. As the initial shortwave tracks into the Midwest/Great Lakes by early Sunday, the 00Z and newer 12Z guidance seems to have steadied in showing deeper solutions with this feature and the associated surface low compared to some previous runs. Guidance still signals potential for some weakening beyond the Great Lakes as the energy aloft may shear out to some degree. Latest GFS/ECMWF runs and their means indicate that the second ejecting western impulse may lead to another wave that reaches the Great Lakes or Ohio Valley on a track farther southeast than the first one and only about a day behind. There is more uncertainty in position and depth with this surface low, and the strongest model thus far is the 12Z GFS. Details of energy behind the second feature become increasingly uncertain, as seen in differences among the operational models as well as broadening spread among ensemble members. The overall trends for this forecast update for day 7 were a deeper trough rebuilding across the West, which is now seen in the 12Z ECMWF and CMC as well, and a faster trend of the cold front tracking farther offshore into the Atlantic. The updated forecast started with primary emphasis on the 06Z GFS/00Z ECMWF with lesser input from the 00Z CMC/UKMET for about the first half of the period, to reflect an intermediate solution among the general clustering that existed for the two primary upper systems and corresponding surface reflection. The reasonably good clustering in the overall pattern but with some greater uncertainty with details of trailing flow led to some addition of the ensemble means particularly by day 7, but still with a majority deterministic model blend. This approach yielded generally modest refinements to continuity other than the aforementioned ones. ...Weather Highlights/Threats... The sequence of two upper systems moving into and through the West from late this week through the weekend should spread rain and higher elevation snow across the region. Most activity should be light to moderate but some locally heavier totals will be possible, primarily from the Sierra Nevada into the Wasatch and central Rockies. With much lower confidence, another system that may drop southeastward into the Northwest early next week may produce some light to moderate precipitation. Meanwhile weather will become more active across many areas to the east of the Rockies from the end of this week into early next week. The first western feature should generate surface low pressure that tracks from the central Plains through Upper Great Lakes during the weekend. The best potential for wintry precipitation types still extends from the northern half of the 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. Latest guidance suggests the storm could be strong enough to produce some brisk winds but model behavior thus far offers potential for additional changes in the forecast. 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. Then there is a continued signal for heavier rainfall potential generally 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 another wave 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. Colder air overspreading the western and central U.S. late this week into the weekend and persisting through at least early next week should yield a broad area of temperatures that are 5-15F below normal. Some pockets of colder anomalies are possible over the northern/central High Plains, particularly in terms of highs. Leading warm sector air, initially focused over the central Plains and then becoming more pronounced over the East, will contain readings that are 10-25F above normal with localized higher anomalies possible for morning lows. Numerous locations over the Southeast may challenge daily record highs from the weekend into early next week, while record warm lows may extend farther northward. 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