Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 AM EST Fri Nov 23 2018 Valid 12Z Mon Nov 26 2018 - 12Z Fri Nov 30 2018 Synoptic Scale Overview ----------------------- Active pattern for the West Coast and the Northeast U.S. next week as a large scale trough settles over the eastern Great Lakes and multiple Pacific lows impact the Pacific Northwest and eventually northern California. Colder than average temperatures are likely for the central states eastward but closer to average west of the Rockies. Model Guidance and Uncertainty Assessment ----------------------------------------- The deterministic models are continuing to have difficulty with the evolution and progression of an elongated upper low centered over the Great Lakes region early next week. There is support for two separate low centers, with greater disagreement with the western upper low across the Upper Midwest. Better model agreement exists for the West Coast ridge on Monday that eventually gives way to a broad upper level trough moving in from the Pacific. As the upper ridge becomes less amplified by mid week over the Rockies, a quasi-zonal flow develops with some hint of a southern stream trough over Mexico and the Gulf, and a closed low reaching the West Coast by Thursday. Given lower than average confidence given the model spread, the forecast relied heavily on the EC and NAEFS means for Wednesday and beyond as a starting point, with some deterministic GFS/ECMWF/UKMET used through Tuesday. Sensible Weather ---------------- A strong low pressure system crossing the Ohio Valley and Great Lakes region on Monday is expected to result in widespread rain from the Mid-Atlantic to southern New England. Snow is likely to the north and west of the surface low across Wisconsin and Michigan, and also for the higher elevations of interior New England and upstate New York. Triple point low should wrap across southeastern New England and into the Gulf of Maine by Tuesday before slowly heading eastward. The Tuesday through Thursday time period should be active for the Pacific Northwest with low elevation rain and higher elevation snow as a lead and secondary system come ashore. Precipitation will work its way southward through northern California by next Thursday. Temperatures will generally be below average over most of the continental U.S. by about 5-10 degrees, especially east of the Rocky Mountains. Hamrick 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