Extended Forecast Discussion NWS Weather Prediction Center College Park MD 118 AM EST Sun Nov 18 2018 Valid 12Z Wed Nov 21 2018 - 12Z Sun Nov 25 2018 ...Record cold temperatures on Thanksgiving for much of the Northeast... ...Overview... Upper troughing in the Northeast Wed/Thu will give way to weak ridging as lead and then reinforcing troughing push through the West. This yields a very cold start to the period in the Northeast and a decidedly wet several days (and white at higher elevations) west of the Divide. To the south, a lingering stationary boundary may try to spin up a surface low and trek across Florida then off the Carolinas next weekend. ...Guidance/Uncertainty Assessment... The models/ensembles have mostly converged on the initial flow evolution out of the Pacific into the West Wed-Fri with a 1-2 punch of systems. For next weekend, again see a lot of spread in the guidance with the central/eastern systems owing to a lack of a well-defined singular trough. Weaker shortwaves will be harder to forecast for a few more days at the least. For now, trended toward the ensemble means which fit in between the GFS/ECMWF solutions with the southern then eastern/coastal system. ECMWF ensemble mean was much more bullish across Florida and off the Southeast coast than the GEFS mean, but it has had better continuity than the GEFS recently. ...Weather Highlights/Threats... Thanksgiving summary (Thu 11/22) - Record cold in the Northeast with high temperatures 15 to near 30 deg F below average and many areas staying well below freezing. Wet along the west coast into the Great Basin and Rockies with near average temperatures and higher elevation snow. Milder and dry for the High Plains with 40s/50s common. Rain chance for the Gulf Coast from Texas eastward through much of Florida to the north of a front in the Florida Straits. The entire west coast and much of the interior will see widespread rain/elevation snow to start the period Wednesday. Precipitation focus still appears to be around northern California and the northern Sierras into southwestern Oregon as the upper trough splits N-S. Multi-day rainfall amounts may be in the 3-6 inch range over favored areas and even about an inch to an inch and a half in the Central Valley. Snow levels will fall through the period with several feet of snow likely at the highest elevations. Much below average temperatures in the Northeast will be slow to ease but will trend back toward typical late November values by next weekend. Temperatures in the west will be near to above average for overnight lows but near to below average for afternoon highs thanks to an abundance of cloud cover. The Plains and Upper Midwest will see milder temperatures Thursday-Saturday, generally above freezing for afternoon highs. Colder air will probably work back south across the border by next Sunday. Fracasso WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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