Extended Forecast Discussion NWS Weather Prediction Center College Park MD 938 AM EST Mon Dec 02 2019 Valid 12Z Thu Dec 05 2019 - 12Z Mon Dec 09 2019 ...Southern tier system to affect the Lower Mississippi Valley/Southeast late week... ...More moisture to spread into the West late this week/weekend and the East by next Monday... ...Pattern Overview and Guidance/Predictability Assessment... A progressive but fairly amplified flow pattern is being dictated by a mid-level vortex across central Canada and a longwave trough moving into the eastern Pacific. Downstream, ridging builds near the West Coast by early next week which acts to slow down the progression of a trough moving through the Southwest. The 00z-06z guidance showed very good agreement into Saturday morning before the 00z Canadian became more progressive with the trough moving through the Southwest, which is not supported by the broader pattern. The pressures, 500 hPa heights, and wind grids were driven by a compromise of the 00z ECMWF, 06z GFS, 00z Canadian, 00z UKMET, and continuity through Saturday morning before the UKMET and Canadian are replaced by the 00z bias corrected NAEFS mean and 00z ECMWF ensemble mean. This led to some slowing of the trough moving through the Southwest but otherwise maintained reasonable continuity. For weather, sky cover, temperatures/extremes, and dew points, used a little bit of the 00z Canadian early. For QPF, tried to tame the 12z NBM and 06z in-house ensemble bias-corrected QPF for day 7 (next Monday) as they looked way too wet considering the model spread and the lower deterministic QPF maxima seen on the 06z GFS, 00z ECMWF, and even the wet 00z Canadian. ...Weather Highlights/Threats... Expect relatively light southern Rockies precipitation to taper off Thursday with the responsible southern tier system bringing a brief period of locally moderate/isolated heavy rainfall to the Lower Mississippi Valley and parts of the Southeast Thursday night-Friday before being suppressed to the south. Moisture ahead of the eastern Pacific system should reach the West Coast late this week and then spread inland over the West through the weekend. Consistent signals from the guidance point to the greatest rainfall/higher elevation snowfall totals focusing over favored terrain in the Sierra Nevada and across northern California, possibly extending into the extreme southwest corner of Oregon. The Pacific Northwest as well as windward terrain across the northern two-thirds of the Interior West/Rockies will see less extreme but still meaningful totals. The upper trough and leading wavy cold front should reach far enough eastward for precipitation (mostly rain) to expand over the eastern half of the country by next Mon. Some activity may be locally heavy if the orientation and timing of the upper trough allow for sufficient input of low level Gulf moisture. Earlier in the period expect one episode of lake effect snow to taper off to the lee of the eastern Great Lakes on Thu followed by a modest event over the northern/eastern Great Lakes and New England approximately Thursday night-Friday night. Locations near the East Coast should see near to moderately below normal temperatures from late week into the weekend. New England may see readings as much as 10-15F below normal Saturday into early Sunday. Clouds/precipitation associated with the upper trough progressing inland from the Pacific will spread above normal morning lows across the West into the weekend while maintaining moderately below normal highs over the Great Basin/Southwest. Cool highs will expand into the Rockies by the start of next week. Meanwhile expect a pronounced warming trend over the eastern half of the country is expected Sunday into Monday, with a broad area of 10-20F+ warm anomalies for morning lows and pockets of 10F+ or so positive anomalies for highs. Roth/Rausch 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