Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1100 AM EST Thu Nov 22 2018 Valid 12Z Sun Nov 25 2018 - 12Z Thu Nov 29 2018 ...Midwest to Great Lakes/Northern New England Winter Weather Threat... ...More Wet Weather from the Northwest into California... ...Overview... Models and ensembles overall agree to show an active pattern next week for the northern corners of the lower 48 next week as troughing aloft settles into the Midwest/Great Lakes and Pacific systems push into WA/OR and through northern CA. A lead system provides a significant winter weather threat on its north side from the mid-MS Valley northeastward over the Great Lakes and northern New England Sunday into midweek. Periods of enhanced rains/elevation snows will also be on the increase for the Northwest and into CA next week. ...Guidance/Uncertainty Assessment and Weather Highlights/Threats... ... Latest GEFS and ECMWF ensemble means provide a good starting point to the forecast for the Sun-Tue period, with lingering timing/amplitude differences especially over the eastern third of the nation still more rampant in the deterministic models. A lead system has had quite poor consistency in the guidance near southern New England on Sunday as an initial trough exits the coast with a southern system exiting through Bermuda. Again tried to stay near the ensemble mean consensus, but the deterministic models have not settled onto a common solution. This would support some heavier coastal rains and interior/northern New England snows to end the extended holiday weekend. Upstream, recent GFS runs have been generally more progressive than the ECMWF and UKMET/Canadian with the upper trough and surface low/front moving out of the mid-Mississippi Valley Sunday. Multi-day trends support slightly slower than composite solution, especially with time. Flow progression should slow next week as strong upper ridging asserts itself over northeastern Canada to block the flow out to the northeast. By next Wed-Thu, the eastern system will slowly exit to the east as the upper low gets trapped over Ontario and then reinforced from central Canada. This could produce some higher elevation snow and perhaps a somewhat localized heavy rain event for southern Maine. In the west, renewed troughing will attempt to push inland into the briefly re-established ridge early next week, but may take another push of upper troughing to finally knock it down by Wednesday and Thursday per the ensembles. The ECMWF still seems too aggressive to lower heights while its ensemble mean seemed more reasonable, though certainly quicker than the GFS/GEFS mean that has been more inconsistent with upstream Pacific system developments over the past few days. Prefer a composite that would now delay ridge weakening a bit more than WPC continuity. There is still quite a bit of forecast spread, but ridges often find a way to remain longer than originally forecast. Schichtel 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