Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sat Oct 10 2020 Valid 12Z Tue Oct 13 2020 - 12Z Sat Oct 17 2020 ...Overview... After the remaining moisture associated with Delta departs New England later on Tuesday, a cold air mass associated with a broad upper-level trough is forecast to work its way across the country from the Pacific Northwest to the Northeast next week, accompanied with a period of rain and high elevations snow for the northern tier states. The next shortwave from western Canada could be dipping into the Pacific Northwest/northern Rockies by next weekend. ...Guidance Evaluation/Preferences... Model guidance generally shows better than average agreement on the synoptic evolution relevant to the U.S. through the medium range. A general blend of the global model outputs from the 00Z ECMWF/EC mean and the 06Z GFS/GEFS were used to compose this morning's WPC prognostic charts. Even by Day 7, models still maintain a relative good agreement with one another. The ECMWF opens the possibility for a low pressure system to develop on the lead cold front in the vicinity of New England by next weekend. The GFS remains relatively progressive with the cold front however. Therefore, more of their ensemble means were incorporated to handle the uncertainty. The shortwave dipping across western Canada toward the Pacific Northwest next weekend is also showing less model spread than usual, including the CMC. Therefore, the above-mentioned blend was thought to be sufficient to handle the situation through Day 7 for now. ...Weather/Hazard Highlights... Some light to moderate rain is expected over the Northeast due to a better-defined low pressure wave associated with post-tropical Delta that the global models are now forecasting to develop off the New England coast Tue-Wed. A cold air mass associated with a broad upper-level trough is forecast to work its way across the country from the Pacific Northwest to the Northeast next week, pushing a swath of rain from west to east across the northern tier states, with some lake-enhanced rain totals possible over the Great Lakes. The Northwest can expect precipitation particularly on Tuesday in the form of lower elevation rain and higher elevation snow, with higher totals over favored terrain. Another round of precipitation will appear to reach the interior Pacific Northwest to the northern Rockies by next weekend as the aforementioned shortwave dips toward the region. Farther south, the lead cold front accompanied by limited moisture is expected to traverse much of the eastern two-thirds of the country and spread somewhat cooler than average temperatures from west to east reaching the Eastern Seaboard by next Saturday. Rain may develop more in earnest over New England next Saturday depending on whether a low pressure system will develop there. Warmer than average temperatures are initially forecast in the East, and morning lows could be 10-20 degrees above normal across the Southeast to Mid-Atlantic Tue. Given the upper ridging over the West, warmer than normal temperatures are forecast for California toward the central Great Basin and Desert Southwest. Upper 90s to low 100s are forecast for the lower deserts of AZ/CA/NV, which could be near high temperature records at some locations. Meanwhile, rain will linger across southern Florida due to a lingering front together with ingestion of some tropical moisture from the south. Kong 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