Extended Forecast Discussion NWS Weather Prediction Center College Park MD 240 AM EDT Fri Oct 09 2020 Valid 12Z Mon Oct 12 2020 - 12Z Fri Oct 16 2020 ...Modest rainfall expected across the Great Lakes and Mid-Atlantic to Northeast... ...Cooler temperatures and precipitation expected for the Northwest... ...Overview... Upper troughing is forecast to progress eastward and push a cold front across the central/eastern U.S. through the first half of next week before slowing as the parent upper low over central Canada also slows. Though Delta should be absorbed in the midlatitude flow by the medium range period, its moisture combined with the front to focus it could lead to modest rain for the northeastern quadrant of the U.S. Favorable moist flow and a cold front are expected to bring precipitation to the Northwest continuing from the short range. ...Guidance Evaluation/Preferences... While the longwave trough pattern moving through the north-central U.S. and broadening late in the week seems likely in most model guidance, the less certain aspects of this forecast are with shortwave energy traversing the trough. Around Wed, 12Z ECMWF/UKMET took a potent shortwave across the Northeast, while the 12Z/18Z GFS runs did not have this feature. At that time, the 12Z EC mean indicated a better defined negatively tilted trough axis across the Great Lakes/Ohio Valley compared to the flatter and farther west 12Z/18Z GEFS means. The most pronounced model differences, however, were with the 12Z CMC, which was excluded from today's model blend as it gave a solution that looked similar to old model runs from the GFS/ECMWF that they have since trended away from for multiple runs. The mid/upper flow west of the trough axis is also in question with this forecast, as ensemble members showed various degrees of troughing/ridging. Overall, did not want to focus on any particular solution considering the uncertainty, and ended up with a model blend mainly containing the 12Z EC and mean and 18Z GFS and mean, with more emphasis on the means later in the period. ...Weather/Hazard Highlights... The cold front moving across the central/eastern U.S. combined with above average moisture from the remnants of Delta should lead to a broad 1-2 inches of rainfall across portions of the Great Lakes region into the Mid-Atlantic and Northeast. Some higher local amounts might result in minor flooding. Ahead of this front, warm temperatures are forecast, especially for morning lows, which Mon/Tue could be 15-20 degrees above normal across the Ohio/Tennessee Valleys to Mid-Atlantic. Farther west, a cold front should move across the Northwest Tue before sweeping across much of the country as the week progresses, causing maximum temperatures to be below normal by 5 to 10 degrees behind it. The main change to continuity in this forecast was to speed up that front's movement given recent guidance. Moist onshore flow should lead to continued precipitation in the northwestern U.S. especially through midweek, with favored terrain seeing heavier amounts, while the higher elevations likely see snow. 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