Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1045 AM EST Sun Nov 03 2019 Valid 12Z Wed Nov 06 2019 - 12Z Sun Nov 10 2019 ...Pattern Overview and Guidance/Predictability Assessment... The large scale pattern across the CONUS shows above average predictability during the medium range. A building ridge from the northeastern Pacific north to Alaska and British Columbia will favor a mean upper trough downstream over the east-central U.S. The main difference among the guidance becomes evident Thu into next weekend 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. Differences hinge largely in the timing of a shortwave crossing the Upper Midwest/Great Lakes/Northeast Thu-Fri. Models were broken into two significant camps surrounding this feature, with the 00Z ECMWF/CMC slower and a bit deeper with the shortwave, and the 00Z UKMET and 00Z/06Z GFS quite a bit faster. The slower solutions develop a more significant wave off the Eastern Seaboard whereas the faster solutions move the front out to sea quickly. Another notable differences in the GFS was that the trailing end of the front interacts with a stronger southern stream impulse, causing a wave of low pressure to develop across the Southeast Thu night-Fri night. At this time based on an assessment of ensembles as well as run-to-run consistency, opted to go more toward the ECMWF/CMC solutions. This idea keeps better WPC continuity and seems more plausible considering favorable upstream ridge amplitude and baroclinic/dynamic environment to feed upon for development. However, confidence in this aspect of the forecast is not high considering the short wavelength spacing between the progressive impulses embedded with the larger scale flow that dig and carve out the e-central U.S. upper trough from a distant source region over northeast Asia and the Arctic/Alaska. By the end of the forecast period late in the week, a relatively strong North Pacific flow regime should persist, with forecast confidence in the timing of specific shortwaves reaching the CONUS relatively low despite somewhat above average consensus on the large scale pattern. The WPC forecast was initially based heavily on the 00Z ECMWF/CMC solutions during days 3-5 (Tue-Thu). After that time, a blend of the ECMWF along with majority ECENS/NAEFS ensemble means was used. ...Weather Highlights/Threats... Expect mainly dry conditions for much of the West except until late week as Pacific moisture spreads inland into 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 mainly snows swaths over the cooled U.S. northern tier from the Rockies through the Great Lakes/Northeast where activity will be prolonged by lake effect. Recent guidance trends show an increasing signal for overrunning precipitation north of a surface front across the Southern Plains Wed into Thu, with the potential for a couple inches of rainfall. Strong high pressure and cold temperature well north of the surface front, from the central Plains and Mid-Mississippi Valley to the Ohio Valley and Northeast, could result in a risk of wintry precipitation whose threat would be enhanced with aforementioned organized frontal then potential coastal low development. Schichtel/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