Extended Forecast Discussion NWS Weather Prediction Center College Park MD 204 AM EST Wed Mar 09 2022 Valid 12Z Sat Mar 12 2022 - 12Z Wed Mar 16 2022 ...Winter storm continues into early Sunday for parts of the Northeast... ...Overview... Amplified troughing in the East to start the period will support strong cyclogenesis and rapid deepening of a surface low through the Northeast on Saturday. This classic spring system will bring snow to the north/northwest of the low, and rainfall exiting the East Coast, with chilly weather to follow through the eastern third of the nation this weekend. Meanwhile, the next shortwave moves into the Northwest on Sunday, with a very uncertain evolution as it moves into the East early next week. Upper ridging should build across the Central U.S. late period, as another, stronger, trough moves into the West next Tuesday-Wednesday. ...Guidance Evaluation/Predictability Assessment... On the large scale, models continue to hone in on a significant East Coast system by the start of the period on Saturday. Details are starting to be worked out as well, with explosive deepening likely up the Northeast Coast into Sunday. The 12z/Mar 8 run of the CMC was a little faster/farther east with the surface low, but the 00z run seems to have come in line. A general model blend of the deterministic solutions seems to represent well for this low. A shortwave into the Pacific Northwest on Sunday shows good agreement on timing, but significant uncertainties begin to arise farther downstream. The ECMWF has been consistently much more phased/quicker with the trough as it amplifies and moves into the East early next week. Meanwhile, the GFS has been pretty consistent with a separation of streams with the southern stream closing off a low over the South. Yesterdays 12z run of the CMC was a nice middle ground. For the new 00z runs today (available after forecast issuance time), the GFS stayed consistent with itself, the CMC sped up to look like the 12z EC, but the 00z EC showed the most dramatic shift, with a closed low feature (albeit quicker than the GFS). There is enough support for that stronger feature in various ensemble members (both from the EC and the GFS) to show a hint of a shortwave/system over the Southeast towards the end of the period in the ensemble means. The next trough into the West Tuesday-Wednesday shows some timing uncertainty (GFS faster, EC/CMC slower). The WPC forecast after day 5, trended rather quickly towards the ensemble means to help mitigate these differences, though did keep minor pieces of the GFS and CMC which kept some semblance of a system across the Southeast early next week. ...Weather Highlights/Threats... Moisture ahead of the strong cold front in the East will continue showers and storms along the boundary across the Southeast, Mid-Atlantic, and coastal New England, with rain changing to snow likely for northern and inland regions as temperatures plummet behind the cold front. Meanwhile, strong dynamics aloft and colder air wrapping around the low should support a winter storm threat and accumulating snowfall Saturday into early Sunday across portions of the interior Northeast, especially northern Vermont, New Hampshire, and Maine. As the low pressure deepens rapidly on Saturday, gusty winds are likely to accompany the system across much of the Eastern states, with winds continuing into Sunday as well for New England as the storm quickly pulls away. Behind the front, much below normal temperatures are expected from the lower Mississippi Valley through the Ohio Valley on Saturday, and into much of the East by Sunday, with daytime highs 20-30 degrees below normal in some places. Even for parts of northern Florida and the Southeast, low temperatures Sunday morning could be near or below freezing with record lows possible in some locations. Meanwhile, rain and mountain snows are likely across the Northwest next weekend with the passage of the first shortwave. The next trough early next week looks poised to direct a possible atmospheric river towards the Pacific Northwest with heavy rain and higher terrain snow possible across western Washington/Oregon and northern California, with additional snowfall farther inland across the northern Rockies. Upper level ridging ahead of this will build across the central U.S. with daytime highs 10 to 20+ degrees above normal by next Tuesday for the northern/central Plains, which should be a welcome relief to the very chilly weather expected later this week. Rain chances should also increase again over the Gulf Coast and Southeast next Monday-Tuesday. Santorelli 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 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