Extended Forecast Discussion NWS Weather Prediction Center College Park MD 226 AM EDT Fri Oct 2 2020 Valid 12Z Mon Oct 5 2020 - 12Z Fri Oct 9 2020 ...Overview and Guidance/Predictability Assessment... The forecast period begins on Monday with an eastern U.S. trough and an upper level ridge over the Desert Southwest and West Coast region, and the trough over the eastern U.S. is reinforced by a second shortwave and cold front arriving from the Great Lakes region. The ridge axis gradually moves east over the western High Plains and loses some amplitude as the flow becomes more zonal over the north-central U.S. towards the end of the week. Overall, the deterministic and ensemble model guidance is in very good agreement on the synoptic scale through Tuesday night with above average confidence, largely owing to the nature of the amplified pattern that is expected to be in place. The main difference during this time is the speed of the shortwave trough over the Mid-Atlantic region and the Northeast that generates an offshore nor'easter, with the 12Z ECMWF and the EC mean slower compared to the 00Z guidance that includes the CMC, GFS, and UKMET. With the second trough crossing the Midwest and Great Lakes region on Tuesday, the CMC is a little faster than the other guidance. By the end of the forecast period, the greatest model differences reside across the West Coast region where confidence is lower, with the ECMWF and CMC indicating a weak upper trough trying to build in, and the GFS/GEFS mean keeping more of the upper ridge in place with the trough well offshore. The fronts/pressures forecast was primarily derived from a blend of the CMC/GFS/ECMWF, along with some previous WPC continuity through mid-week, and then introduced more EC mean and GEFS mean for Thursday and Friday. ...Weather/Hazard Highlights... The nor'easter that is likely to develop over the offshore waters of the Northeast U.S. will likely have some rain and wind impacts for portions of eastern New England, with the worst conditions expected to remain offshore. There will likely be some showers in the vicinity of the Great Lakes and the Ohio Valley through midweek as the upper level trough builds in and some instability develops, along with breezy to windy conditions. Periods of heavy showers and some thunderstorms may also persist for South Florida owing to the lingering frontal boundary that should slowly wash out. Elsewhere, with the exception of some showers for the Pacific Northwest, a quiet weather pattern is expected in terms of precipitation for most other areas next week. The upper ridge persisting across the West should continue to result in hot and dry conditions, along with associated wildfire risks. Expect temperatures to be 5-15 degrees above normal from the Desert Southwest to the Northwest, and this will likely expand eastward to the central/southern Plains by the middle of next week. A cooling trend should then commence across the Pacific Northwest by next Thursday. In contrast, a reinforcing cold air surge early in the week will generally keep temperatures about 5-15 degrees below normal for much of the central to eastern U.S., making it feel truly autumnal outside. In terms of the Tropics, there will be two disturbances that are being monitored by the National Hurricane Center, with the western-most feature having the greatest likelihood of developing into at least a tropical depression over the next several days. Although these systems are currently expected to remain south of the U.S. Gulf Coast region, they will continue to be watched as they track westward. Hamrick 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