Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1147 AM EDT Sat Nov 02 2019 Valid 12Z Tue Nov 05 2019 - 12Z Sat Nov 09 2019 ...Pattern Overview and Guidance/Predictability Assessment... Overall, the large scale pattern across the CONUS shows slightly above average predictability during the medium range. A building ridge from the northeastern Pacific north across Alaska toward the Arctic will favor a persistent and broad upper trough across the north central/northeastern U.S. The primary difference among the guidance emerged by by late on day 5 (Thu) into days 6-7 (Fri-Sat) with respect to a potential wave of low pressure along the surface front across the Ohio Valley/Appalachians to off the Northeast U.S. coast. A trend was noted across some of the 00Z guidance toward a more significant wave of low pressure, as shown by the ECMWF and CMC. The GFS, on the other hand, moves any potential weak wave of low pressure eastward and well offshore much more quickly. Given an increasing number of ensemble members showing something along the lines of the ECMWF/CMC, felt compelled to adjust the forecast at least somewhat in that direction, although confidence in this specific aspect of the forecast is low, as as typical of such systems in the medium range. The WPC medium range forecast was initially derived from a multi-model deterministic blend including the 00Z ECMWF/CMC/UKMET/06Z GFS during days 3-5 (Tue-Thu). Weighting of ensemble means (ECENS and NAEFS) was increased by days 6-7 (Fri-Sat), with some continued emphasis on the deterministic ECMWF/CMC solutions, showing the potential for an area of low pressure near/off the Northeast U.S. coastline by late next week. ...Weather Highlights/Threats... Expect mainly dry conditions for much of the West except into later next week as Pacific moisture feeds into/through Pacific Northwest terrain. The downstream pattern will favor the spread and periodic reinforcement with colder than normal airmasses from the Rockies and Central U.S. to the East as post-frontal high pressure cells spill down from Canada. High temperatures are forecast to be as much as 10-20 deg F below average across much of the central and eastern U.S. next week as the strong Canadian high pressure moves southward into the U.S. Moisture will be mainly limited across the mid-higher latitudes, but the passage of several clipper lows should support modest snows/light rain swaths over the U.S. northern tier from the Rockies through the Great Lakes/Northeast where activity will be prolonged by lake effect. The latest model runs have shown an increasing signal for a potential overrunning precipitation north of a surface front across the Southern Plains Tue night-Thu, with the potential for a couple inches of rainfall. Strong high pressure and cold temperature well north of the surface front, from the Mid-Mississippi Valley to the Ohio Valley, could result in the potential for at least some areas of wintry precipitation, although confidence in the specifics is low at this time. Ryan 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