Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1104 AM EST Tue Nov 06 2018 Valid 12Z Fri Nov 09 2018 - 12Z Tue Nov 13 2018 ...Guidance/Predictability Assessment... An amplified pattern is exhibited in the medium range period--primarily with a trough in the eastern U.S. and a strong ridge centered over the western U.S. On Friday and into Saturday, a mid-upper level trough will dig across the Upper Midwest to Great Lakes--with troughing extending into the Desert Southwest. The 06Z GFS/00Z ECMWF also show a mid-level disturbance sliding down into the Intermountain West and northern High Plains during this time period as an upper level ridge begins building over the West Coast. As this digging trough over the Great Lakes swings northeast over the Canadian Maritimes, the disturbance that tracked over the Intermountain West will develop a mid-upper level trough over the central U.S., with the upper level ridge maintaining its position in the West. This trough will continue to dig as it slides eastward over the East Coast. The ridge finally begins to shift inland, with height falls expected over the Pacific Northwest by the end of the medium range period. Overall, both the 06Z GFS/00Z ECMWF were agreeable even through day 7, as were their ensemble means. One of the biggest outliers was the 00Z CMC, showing a closed mid-upper level low digging over the Central Great Basin, but even the 00Z CMC ensemble mean did not show this. Thus, WPC used a 06Z GFS/00Z UKmet/00Z ECMWF blend with the ensemble means and increasing the means more by Days 6/7. However, because the GFS/ECMWF were lining up well even through day 7, these operational models were used through the end of the medium range period. ...Weather Highlights/Threats... As the mid-upper level trough moves across the central to northeastern U.S. on Friday and Saturday, a cold front will push through the Ohio Valley/lower Mississippi valley eastward toward the East Coast. Along and ahead of this front, southerly flow will transport moisture from the Gulf of Mexico--promoting showers and thunderstorms stretching from the Southeast to New England. A stationary front will also linger off the Carolina coast and may contribute to rain near their coastlines. By Saturday, most of the rain will push off the Mid-Atlantic and Southeast but the main low of this front will move into the Northeast and could enhance precipitation along this region. Cyclonic flow across the Great Lakes combined with temperatures cooling behind the front may promote lake effect snows--and could spread into the interior Northeast. Higher elevation snow can be expected through the weekend as the disturbance moves into the Intermountain West. As the next trough develops by Sunday and into Monday, snow could move across the northern Plains and into the Upper Midwest. Another round of showers and thunderstorms will occur in the beginning of the workweek as that trough digs eastward and the surface front pushes across the Southeast. This could bring heavy rain to the central Gulf Coast--with precipitation spreading into the Mid-Atlantic. By Tuesday, rain with snow across the interior of New England can be expected as the occluded front pushes northward through the area along with lake effect snow. Because of the pattern, temperatures will stay below normal for the central and eastern U.S. through the medium range period while the West Coast and parts of the Central Great Basin will experience above average temperatures. Reinhart 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