Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1159 AM EDT Sat Oct 20 2018 Valid 12Z Tue Oct 23 2018 - 12Z Sat Oct 27 2018 ...Guidance/Predictability Assessment and Weather Highlights/Threats... A favored composite of latest models and ensembles that seem reasonably well clustered into day 5/6 agree that a split flow regime will favor a weak southern stream trough track from the Desert Southwest toward the middle of the country next week. Some phasing with a northern branch of the jet could lead to cyclogenesis across the northern Gulf of Mexico with the frontal wave tracking toward the southeastern U.S. that likely offers a threat of heavy rainfall along the Gulf Coast and northern Gulf of Mexico/Florida. There is a subsequent threat for significant low/storm deepening up off the eastern seaboard next weekend to monitor the WPC product suite by days 6/7 was more in line with a blend of ensembles and WPC continuity amid growing forecast spread and uncertainty. Across the more northern latitudes, lower heights should tend to work into northeastern North America as an upper low continues to spin over northern Nunavut. Amplifying flow swinging through the Great Lakes will ultimately aid in the development of a coastal wave in the vicinity of Nova Scotia by late Tuesday/early Wednesday. Northern Maine could see some snowfall accumulations as the coastal low takes shape. Back to the northeastern Pacific, multiple deep cyclones are likely to approach western British Columbia during the Day 3-5, October 23-25 timeframe. While most of the action should stay north of the international border with Canada, the mean flow should turn more zonal across the eastern Pacific allowing more of an onshore flow regime into the Pacific Northwest. The persistence of onshore flow will keep a steady focus for upslope driven rainfall across the Olympics and Washington Cascades. Toward next weekend, broad ridging is forecast to gradually encompass the eastern Pacific with longwave troughing expected to cover the middle of the country. It appears the better activity will hold off until later in the week as the mean flow turns more zonal in nature. Generally speaking, outside of the mentioned areas of cyclogenesis, synoptic-scale gradients should remain on the more washed out spectrum across the remainder of the nation. Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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