Extended Forecast Discussion NWS Weather Prediction Center College Park MD 120 AM EST Mon Nov 9 2020 Valid 12Z Thu Nov 12 2020 - 12Z Mon Nov 16 2020 ***Active weather pattern across the northwestern U.S. and Tropical Storm Eta a threat to portions of Florida*** ...Pattern Description... An active storm track will be in place across the northeast Pacific with both a northern and southern stream component to the mid-upper level flow. The upper level ridge axis that is currently in place near the East Coast is expected to be shunted a little farther to the east over the western Atlantic as shortwave energy approaches from the Plains. The pattern may evolve to a more quasi-zonal pattern by the beginning of next week, compared to earlier in the forecast period, with a broad trough over the east-central U.S. Tropical Storm Eta is forecast to track towards the northeast and weaken as it eventually enters the western Atlantic and becomes extratropical in nature. ...Guidance Evaluation/Preferences... Given the active dual-stream flow pattern expected for the end of the week and weekend, the overall degree of model spread has increased some compared to recent days. Forecast confidence is highest across the central U.S. and extending to the East Coast outside of the effects of Eta. The 00Z GFS becomes a considerably faster solution by Saturday night across the Plains with the trough, and this becomes even more apparent by Sunday into Monday when this solution starts to be out of phase with the model consensus. However, forecast confidence is limited for the Pacific Northwest and the Intermountain West owing to both timing and amplitude differences over the northern Pacific. There is some indication in the deterministic guidance, particularly the 00Z GFS and 12Z CMC, for a powerful occluded surface low to approach the Washington/Oregon coast on Friday, whereas the UKMET was more intense with this low on earlier runs compared to it 00Z run. Ensemble means provided more of a reasonable baseline for the forecast here, so that was incorporated heavily into the forecast along with some previous WPC continuity. The WPC forecast followed the National Hurricane Center track for Tropical Storm Eta. In general, slower movement is expected over the eastern Gulf compared to yesterday's and previous forecasts, with a weak upper trough over the Gulf complicating the forecast. Any potential landfall over central Florida during the second half of the week remains highly uncertain in position and timing, with model and ensemble guidance showing a myriad of solutions from landfall in the Florida Big Bend to a re-curve southwestward staying over the Gulf. The National Hurricane Center has additional information pertaining to this storm. ...Sensible Weather and Hazards... The western U.S. trough will result in below normal temperatures for much of the interior western through Thursday, before a gradual moderating trend commences. An extended period of unsettled weather is forecast to move across the Pacific Northwest by the end of the week and beyond, with heavy mountain snows spreading eastward to the northern Rockies, particularly across Idaho. Numerous showers, heavy at times, will also be likely west of the Cascades through much of next week under an active upper-level pattern across the northeastern Pacific, and a potential atmospheric river event during this time. Several inches of rainfall is becoming more likely. Tropical storm Eta is forecast to slowly track north, and then northeast over the eastern Gulf, bringing heavy rain and potentially tropical-storm-force winds for portions of the western Florida coast. Given the remaining uncertainty in the long range track, it is much too early to speculate where any landfall happens. Elsewhere, mild late fall weather should continue across much of the eastern U.S. through the end of this week, with temperatures that are expected to be up to 15 degrees above normal. However, moisture interacting with a slow moving front will likely bring a swath of heavy rainfall across much of the Southeast late this week, with one to three inches possible at this time. Hamrick Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php 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