Extended Forecast Discussion NWS Weather Prediction Center College Park MD 307 PM EDT Sat Oct 03 2020 Valid 12Z Tue Oct 06 2020 - 12Z Sat Oct 10 2020 ...Tropical moisture associated with Tropical Storm Gamma and another possible tropical wave could spread heavy rain to Florida and eventually the Gulf Coast states... ...Overview... Broad cyclonic flow is expected across the north-central U.S. and the Northeast through the end of the week emanating from a potent mid/upper low over the Hudson Bay Tue-Thu before moving east. An upper-level ridge will initially be present across the western third of the U.S. at the beginning of the forecast period Tue, shifting into the central U.S. and flattening through the rest of the week. Meanwhile, troughing is forecast to develop in the eastern Pacific and affect the West Coast late in the week. A surface front will serve to focus tropical rains over Florida, with the Gulf Coast potentially seeing some rain by Fri/Sat. ...Guidance/Predictability Assessment... Model guidance is in good agreement through midweek especially with the persistent troughing in the central to eastern parts of the country. A multi-model deterministic blend was able to be used for the fronts/pressures forecast early in the medium range period. Differences in the models emerge particularly over the eastern Pacific with the timing and position of the trough and energy within it. Beginning around Thu, the 00Z ECMWF developed and shifted this trough farther east than the slower GFS runs, with the 00Z CMC in between. This faster timing of the ECMWF persists through Fri/Sat as it brings the upper trough influence into the Pacific Northwest sooner than other guidance. The differences in the deterministic models also impact the degree of ridging or zonal flow that will take place in the central U.S. later in the week. In general, the differences seemed great enough to lean away from any individual solution and focus on the GEFS/ECENS ensemble means late in the period. ...Weather/Hazard Highlights... The tropics are becoming active once again as Tropical Storm Gamma is forecast to curve into the Bay of Campeche by the medium range period, and another tropical wave could develop to its northeast in the Gulf of Mexico (see the National Hurricane Center for updates). Tropical moisture from these systems is forecast to continue spreading into Florida, and a surface front could help focus the rainfall to create potentially heavy amounts there. The central and eastern Gulf Coast could also see rainfall by the end of the week depending on how the possible tropical system develops, but uncertainty is still high at this time with amounts and placement. The troughing coming into the Northwest is forecast to spread precipitation to the region, with higher totals over favored terrain. The region should also see above normal temperatures through midweek flipping to near or below normal as the trough approaches. Below average temperatures are expected centered over the Great Lakes region as reinforcing cold fronts come through later in the week. Showers are possible for the Great Lakes to the interior Northeast around midweek. The rest of the U.S. should generally experience dry conditions, and warmer than average temperatures will be widespread across the Rockies to the Plains and Mississippi Valley. The highest temperature anomalies of 10 to 20 degrees above normal are expected in the Northern/Central Plains. 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