Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1209 PM EST Fri Dec 06 2019 Valid 12Z Mon Dec 09 2019 - 12Z Fri Dec 13 2019 ...Heavy rain potential for Mid-South to Northeast early next week... ...Well below normal temperatures over the northern Plains/Upper Midwest early-mid week... ...Pattern Overview and Guidance/Predictability Assessment... A deep vortex that dips south to Hudson Bay this weekend remains centered there through next week. A notable trough rounding this low amplifies across the eastern 2/3 of the CONUS by Tuesday with lesser troughing/cyclonic flow through the rest of week. An upstream ridge amplifies up the North American West Coast early in the week before being weakened through the midweek by shortwave activity off a Gulf of Alaska low. The southern stream flow associated with the amplifying trough early in the week has uncertainty in terms of magnitude and ejection timing across the southern CONUS Tuesday through Thursday. A multi-model deterministic blend works generally well through Day 4/Tuesday with the progression of the positively tilted trough pushing southeast across the western CONUS as the trough amplifies. The 00Z CMC/UKMET are then slower/stronger with the southern stream trough over Texas than the 00Z ECMWF/06Z GFS which is preferred for Day 5/Wednesday. A blend of the 00Z ECENS/06Z GEFS was then favored for Day 6/7 with an understanding that shortwave features crossing the southern/central CONUS will determine the sensible weather, but are washed out by blending the means. This Hudson Bay gyre looks to persist through the middle of the month. The next lobe may be with interaction from eastern Pacific impulse energy/moisture rounding the western ridge which may allow another trough to amplify over the eastern CONUS next weekend. ...Weather Highlights/Threats... There is a strong signal for heavy rainfall to continue ahead of the main cold front with this amplifying trough Monday night from the lower MS Valley to the northern Mid-Atlantic and southern/eastern New England. Locally heavy snow may persist in the comma head of the parent low over the central Great Lakes at this time as well. Lake effect snow should spread across the Great Lakes into Tuesday in the wake of the cold front which is particularly cold. Polar plunges are expected behind the cold front with temperature anomalies of 15 to 30 degrees below normal centered over the Upper Midwest with reinforcing shots of cold air. Jackson 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