Extended Forecast Discussion NWS Weather Prediction Center College Park MD 228 AM EDT Sat Oct 10 2020 Valid 12Z Tue Oct 13 2020 - 12Z Sat Oct 17 2020 ...Overview... Broad troughing is forecast across the central and eastern U.S., while ridging may build across the West late in the week, causing somewhat drier conditions after a bout of rain and higher elevation snow across the Northwest through Tue. ...Guidance Evaluation/Preferences... Generally good model agreement persists regarding the large upper low moving slowly across central Canada, though the 12Z UKMET was sufficiently different from consensus with its positioning to exclude from tonight's blend. The upper low spreads troughing into much of the central/eastern U.S., and details of a couple shortwaves moving through the larger scale flow are coming into better agreement around Tue-Thu. Thus through day 5/Thu, used a multi-model blend of the 18Z GFS, 12Z ECMWF, and 12Z CMC as well as smaller components of the ensemble means. Guidance continues to indicate a building ridge into the western U.S. Thu-Fri as well. By Fri-Sat, the timing and placement of additional energy coming across Alaska and western Canada will influence the flow pattern across the Northwest. Model guidance is especially variable there and this is the least certain part of the forecast, so leaned toward the ensemble means. The 12Z ECENS mean flattens the flow and even creates troughing by Sat, but individual ensemble members have lots of spread. Leaned a little more toward the more amplified 18Z GEFS mean by the end of the period, since given the downstream trough, maintaining the ridging across the Northwest seems reasonable. ...Weather/Hazard Highlights... Some light to moderate rain is expected over the Northeast due to a low pressure/frontal system traversing the area Tue-Wed. Periods of light rain underneath the upper trough are also possible over the Great Lakes region and interior Northeast through the end of the week with some lake-enhanced rain totals, though remaining light. The Northwest can expect precipitation particularly Tue in the form of lower elevation rain and higher elevation snow, with higher totals over favored terrain. Another round of precipitation may be possible there late week depending on how the aforementioned uncertain upper flow and the associated surface front evolve. A cold front with limited moisture is expected to traverse much of the country and spread somewhat cooler than average temperatures across the Northwest Tue/Wed to the Plains/Midwest by Thu and cooling down the Eastern Seaboard by Sat. 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 across 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 set high temperature records. Tate 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