Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1136 AM EST Sat Jan 26 2019 Valid 12Z Tue Jan 29 2019 - 12Z Sat Feb 02 2019 ...Well below normal temperatures expected across much of the north-central U.S. into the Eastern U.S. next week... ...Pattern Overview... The overall pattern during the medium range period features quite amplified flow through next Thursday with a large scale ridge situated over the West Coast, and a large and cold upper level arctic low reinforcing a large trough over much of the central and eastern states. As the deep closed low lifts out into eastern Canada, the pattern across the CONUS shifts and weakens slightly as the western U.S. ridge slides inland and a broad trough becomes established over the eastern Pacific. ...Guidance Evaluation/Preferences... Deterministic models and ensembles remain in good enough agreement with the deep upper level vortex as it tracks along the U.S./Canada border and lifts into eastern Canada near the middle to end of next week. A general model blend sufficed for this system. Model differences in the medium range concentrate in the Western U.S. first with a small lobe of energy embedded within the broad upper level ridge, and again with eventual troughing off the West Coast late next week. Regarding the first system, the deterministic GFS/ECMWF continue to hang onto a small closed low approaching the Pacific Northwest coast early next week, with individual member disagreement lending to a much weaker/suppressed output in the ensemble means. To maintain WPC continuity, did lean more towards the GFS/ECMWF solutions Day 3 and 4. Models really diverge by days 6 and 7 on the evolution of the eastern Pacific trough. There remains plenty of run-to-run continuity in the deterministic runs (regarding broad troughing or a possible closed low off California day 7) to warrant a mostly ensemble mean blend. Leaned very heavily on the ECENS mean over the GEFS mean due to more pronounced troughing, and slightly better overall continuity both with previous runs and the WPC forecast. ...Weather Highlights/Hazards... A clipper system crossing the Great Lakes into the Northeast early in the period should result in a band of moderate to locally heavy snowfall north and west of the surface low across the lower Great Lakes and much of the Northeast. Rain may also change to snow along the main cold front as it crosses the Central/Southern Appalachians, the Mid-Atlantic, and coastal New England. Lake effect snows are likely downwind of the Great Lakes as intense cold air advection continues on the backside of the system. Out west, rain and mountain snows are expected to return to the West Coast by next weekend as a low pressure system works its way towards California. The bigger headline in the medium range period will be brutal, potentially dangerous, cold temperatures diving into the north-central U.S. early next week. Daily high temperatures Monday - Wednesday of next week across much of the Upper Mississippi Valley and into the Midwest are forecast to be below zero for many locations, with overnight mins 20 to 30 below zero! These temperatures would be 30 to 40 degrees below normal, with both daily low and high temperature records likely to be challenged or broken. Although the airmass should modify some by the time it reaches the East Coast during the middle of next week, temperatures are likely to still be well below normal on Thursday with daytime highs below freezing for most locations across the Mid-Atlantic and the Northeast. Santorelli WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation and winter weather outlook probabilities 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