Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1106 AM EST Mon Nov 19 2018 Valid 12Z Thu Nov 22 2018 - 12Z Mon Nov 26 2018 ...Record cold temperatures on Thanksgiving/Black Friday for much of the Northeast/New England... ...Could be the coldest Thanksgiving since 1996 for the DC-PHL-NYC-BOS corridor... ...Overview... Very cold but mostly dry in much of the east while it will be stormy in the western US later this week. A couple of cold fronts will push across the lower 48 and potentially lift up along the East Coast Sat/Sun during a very busy travel time. Above average temperatures in the High Plains will trend back to below average by next week. ...Guidance/Uncertainty Assessment... Model guidance suggest a split flow pattern through much of extended periods, with the southern stream becoming more dominant this weekend. Model differences are apparent after day 3 (Thanksgiving) and continue to increase through the end of the forecast. The last two runs of the GFS continue to be faster while the ECWMF, Canadian, UKMET and ensemble means maintain a slower/west solution. Chose to maintain continuity by using a multi-model blend, using the GFS very sparingly. Guidance continues to depict a pair of fronts converging/slowing over the mid-Mississippi and western Ohio Valleys as the upper trough sharpens. This may take another area of low pressure northeastward but on the west side of the Appalachians next Sun/Mon. Again preferred the slower/sharper solutions unlike the recent quicker/weaker GFS runs. ...Weather Highlights/Threats... A rather chilly Thanksgiving Day is in store for much of the Northeast, lower Great Lakes and northern Mid-Atlantic regions where afternoon highs will hover near 15 to 30 deg F below average. The majority of area will stay well below freezing, while low temperatures may reach the single digits on either side of zero. The much below average temperatures in the Northeast will slowly ease back toward typical late November values by the weekend (and likely above average minimum temperatures). The entire West Coast and much of the interior West will be in a prolonged active, wet pattern. With extensive cloud cover expected, overnight temperatures are forecast to be near or above average through the extended periods. Widespread rain/elevation snow will likely result in multi-day totals of 3-6 inches, especially over the favored upslope areas- even about an inch to an inch and a half in the Central Valley. Snow levels will waver but generally fall through the period with several feet of snow likely at the highest elevations. Across the High Plains, this next week will generally be mild and dry with temperatures mainly in the 40s and 50s, cooling to the 30s and 40s during the weekend. The cooler temperatures will reach the Central Plains/Midwest by the weekend as a cold front passes through. The Gulf Coast has an increasing chance for rain as a low pressure system develops and tracks east across the South and Southeast, which may support the potential for heavy precipitation across portions of the Southeast, Mid-Atlantic, and southern/central Appalachians as the system transitions to a Nor'ester. This may coincide with another very busy travel day on Sunday. Campbell 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