Extended Forecast Discussion NWS Weather Prediction Center College Park MD 136 AM EST Fri Nov 15 2019 Valid 12Z Mon Nov 18 2019 - 12Z Fri Nov 22 2019 ...Pattern Overview and Guidance/Predictability Assessment... During the medium range, relatively amplified and progressive flow from the North Pacific into Canada and the CONUS northern tier will be flanked to the south by a somewhat less progressive southern stream with a tendency for upper-level energy to close off and move a bit more slowly. The ECMWF and GFS showed slightly above average agreement through the medium range, although both have shown some degree of variability over the past several runs, so any consensus is at least somewhat tenuous. Two low pressure systems are forecast to track northward off the Eastern Seaboard, the first on Mon and the second Tue-Wed. ECMWF and GFS solutions showed some timing and intensity differences for these systems, but the solutions were close enough to be used in a blend. Farther west, shortwave energy diving south along the West Coast Mon night/Tue is forecast by the ECMWF/GFS and numerous ensemble members to close off across the Southwest by late Wed, perhaps at least partially interacting with upper-level energy associated with what is now Tropical Depression Twenty-E over the eastern Pacific. Model/ensemble solutions show general consensus that this closed upper low should rather slowly move east across the Four Corners region and southern Rockies by Fri, perhaps reaching the Southern/Central Plains. At the same time, northern stream shortwave energy is expected to amplify across the Great Lakes, pushing a cold front across much of the central U.S. The WPC surface progs were based on a blend of the 12Z ECMWF/18Z GFS as well as the 18Z GEFS mean, along with a substantial weighting of forecast continuity through day 6 (availability of ensemble and some deterministic model data was limited due to network issues during model ingest times). ...Weather Highlights/Threats... Initially chilly temperatures across the eastern third of the nation on Mon, should moderate toward normal by the middle of next week. On the other hand areas from the West into parts of the northern-central Plains will see well above normal temperatures (up to plus 10-20F anomalies), especially Mon-Tue. The lead system off the Mid-Atlantic coast should keep the heaviest rains offshore but could be close enough to produce some rain along the coast. If any moisture extends farther inland it is most likely to be over the Northeast. In that case the western periphery of the moisture shield could contain some snow. The strong pressure gradient between the low and the surface high exiting New England will lead to windy conditions along the coast and especially over the nearshore waters. Please see the Ocean Prediction Center's products for more information. Precipitation coverage and intensity with the second area of low pressure evolving Tue-Thu are more uncertain, with the Northeast again the most likely area to see some rain and inland/higher elevation snow if the moisture shield extends far enough westward. Favored terrain in the Pacific Northwest/northern Rockies will an episode of light-moderate precipitation Mon-Tue. The upper low settling over or near southern California mid-late week would increase the potential for significant precipitation (mostly rain) over the Southwest and in particular central Arizona, especially if additional tropical moisture associated with the eventual remnants of Twenty-E is drawn northward. Remaining western energy aloft progressing across the northern half of the lower 48 may bring a front and accompanying precipitation into the east-central U.S. by next Thu. A potential wave of low pressure along the trailing end of the frontal boundary across the Southern/Central Plains may bring an increase in precipitation to areas from the Plains to the lower/mid-Mississippi Valley as well. Depending on the intensity of the low pressure wave, sufficient moisture advection into the cold air north of the surface front will be possible to produce some winter weather potential from the mid/upper-Mississippi Valley to the Great Lakes. Ryan/Rausch 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