Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1058 AM EST Wed Nov 07 2018 Valid 12Z Sat Nov 10 2018 - 12Z Wed Nov 14 2018 ...Guidance/Predictability Assessment... Overall, models are in good agreement with the synoptic scale features and start deviating slightly by later in the medium range period. During the weekend, the upper low over the Great Lakes will shift north over Canada as another trough develops across the central U.S. to the Central Great Basin. The upper level ridge will stay over the Pacific, just off the West Coast. By Monday and into Tuesday, as the upper level ridge begins to shift inland, the trough will dig across the central U.S. By midweek, the trough will shift over the eastern U.S. as the upper level ridge centers itself over the western U.S. Height falls are expected by Wednesday for the Pacific Northwest as energy from a trough in the Gulf of Alaska works its way into the region. The operational 00Z and 06Z GFS along with the 00Z ECMWF/UKmet were in agreement with the pattern on days 3/4 and even on day 5. By day 6, noticeable differences with timing of the trough moving over the eastern U.S. became apparent. The 00Z GFS was significantly faster by Day 7, having a closed upper low over eastern Canada as the 06Z GFS/00Z ECMWF were still over the Ohio/Tennessee Valley. The 06Z GFS was also slightly faster--but still within a reasonable range of the ECMWF. The 00Z ECMWF ensemble mean and 06Z GEFS mean suggest to lean toward the slower solutions. Thus, WPC used a blend of the 06Z GFS/00Z ECMWF/00Z UKmet in the beginning of the medium range, then shifting to more of the 00Z ECMWF ensemble mean/06Z GEFS mean by days 6 and 7, with a little bit of the 06Z GFS/00Z ECMWF. ...Weather Highlights/Threats... As the first mid-upper level low lifts northward from New England, cyclonic flow over the Great Lakes will encourage lake effect precipitation, some of which could be snow, that may move into the interior of New England. As the second trough digs over the central U.S., moisture will be pulled from the Gulf of Mexico and increase the chance of showers and thunderstorms across the Gulf Coast by the end of the weekend and into early next week. As the trough shifts east, so too will the precipitation--spreading across the Tennessee and Ohio Valleys along with the Mid-Atlantic on Tuesday and into Wednesday. In fact, there continues to be a growing signal supporting ample leading wave/frontal genesis and deep moisture return to would fuel heavy rain/convection expansion northward across the east-central then eastern U.S. Additionally, moisture feeding back into a sharpening baroclinic zone could give way to organized snow threat through the Appalachians/Ohio Valley, with ample lake effect enhancement lee of the Great Lakes and for the interior northern Mid-Atlantic and Northeast with system approach. Significant early season snows are possible. As the Pacific trough energy moves into the Pacific Northwest, an increase in precipitation can also be expected during the middle of next week. In terms of temperatures, the eastern U.S. will be anomalously cold--from the Northeast southward to the Gulf Coast. In fact, high temperatures may only reach the mid-50s along the western and central Gulf Coast on Tuesday and Wednesday. The upper and middle Mississippi Valley may see high temperatures only reach the mid 20s to mid 30s. The western U.S. will continue to experience above average temperatures. Reinhart/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