Extended Forecast Discussion NWS Weather Prediction Center College Park MD 146 AM EST Thu Jan 02 2020 Valid 12Z Sun Jan 05 2020 - 12Z Thu Jan 09 2020 ...Overview/Guidance Assessment... Models and ensembles generally show good agreement that the synoptic pattern across the U.S. will be dominated by a progressive west-to-east flow. Some uncertainty regarding track and intensity of embedded shortwaves is the main concern, one of which could amplify into a significant cyclone for the eastern half of the country by the middle to later part of next week. The medium range period begins Sunday with an initial deep cyclone exiting the Northeast coast. The UKMET and CMC are displaced farther away from the coast with the low center, with the ECMWF/GFS and ensemble low clustering closer to the coast. Preferred a blend of the ECMWF/GFS with this system which also fits with previous shift continuity. Meanwhile, another shortwave will be entering the West Coast on Sunday, and models generally agree that this feature will track across the Rockies, and emerge into the Plains late Monday. There remains some question on amplitude which in turn translates to potential development of a surface low over the Central U.S. on Monday, deepening as it moves into the Northeast on Wednesday. The ECMWF has remained consistent in showing a rather amplified shortwave, though the GFS has trended more amplified with its previous past couple of runs. The latest CMC is by far the slowest and strongest with the shortwave and was not a preferred solution. The GEFS mean is quite a bit slower than its deterministic counterpart, with the ECENS mean and NAEFS mean more closely in line with the GFS/ECMWF (just weaker/more washed out). Prefer a blend of the GFS/ECMWF with contributions from the ECENS/NAEFS means. Put a bit more weight on the ECMWF over the GFS only because of its better/more consistent run to run continuity. It is important to note there is still quite a bit of uncertainty in the track of the surface low, or even if one will exist at all. At this point, WPCs forecast does show low pressure tracking from the Southern Plains on Monday to off the Northeast Coast by Wednesday, though not nearly as strong as some of the deterministic guidance would suggest. Another shortwave enters the West Coast by Day 7, and again there are questions on both amplitude and timing of this shortwave. Given the time range at this point, preferred to stick close to the ensemble means with this feature for now. ...Weather Highlights/Threats... Some wintry precipitation should be exiting New England with the departing surface low on Sunday, with favorable westerly/northwesterly flow providing some lake effect snows downwind of the Great Lakes. Daily surges of moisture will keep precipitation likely across the Northwest into the Northern Rockies during the period, focusing more over coastal locations and the Coastal Range/Cascades. Depending on the evolution of the trough/surface low development across the Central U.S. day 4-6, some snow may be possible north and west of the low across parts of the Ohio Valley to the Northeast toward the end of the period, with rainfall farther south. Confidence remains low at this time regarding the details. With a fast west-to-east flow across the country, no severe outbreaks of arctic air is anticipated. This will lead to temperatures averaging near to slightly above normal with relatively short periods of colder than normal temperatures behind departing storms. Santorelli Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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