Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Tue Nov 05 2019 Valid 12Z Fri Nov 08 2019 - 12Z Tue Nov 12 2019 ...New England coastal storm and heavy snow threat Friday... ...Multiple cold air surges to winterize the central and eastern U.S... ...Pattern Overview and Guidance/Predictability Assessment... Guidance still depicts an amplified West Coast/Alaska ridge and e-central U.S. trough upper pattern over medium range time scales that tends to have above average predictability for the large scale flow. However there are lower-confidence embedded details that will be important for resolving sensible weather effects. This favors a composite guidance blend that is now more reasonable as the models and ensembles are finally converging upon a more common solution with respect to potentially deep storm development off the Northeast U.S. by Day3/Fri and the Canadian Maritimes into the weekend. The GFS/UKMET are now more in line with recent runs of the ECMWF/CMC. The stormy solution has been best supported by GEFS and especially ECMWF ensembles along with WPC continuity over the past number of days. By early next week, recent GFS/ECMWF runs and their ensembles means further open the possibility for greater amplification/depth of the next shortwaves set to dig into the long-term mean trough over the east-central U.S. This seems to support coastal low developments off the Eastern Seaboard. WPC progs show modest low developments given uncertainty that are albeit close enough offshore to effect coastal areas and maritime interests given how far west/inland the main upper trough axis is dug. ...Weather Highlights/Threats... To the west of the Rockies expect mainly warm and dry conditions. One exception may be with some modest Pacific moisture/precipitation that may work into the West Coast mean upper ridge position into Pacific Northwest terrain. The downstream pattern under a mean upper trough position laden with embedded shortwave impulses favors periodic reinforcement of colder than normal temperatures from the Rockies and Central U.S. to the East as post-frontal surface high pressure centers track south/southeast from Canada. A lead cold airmass will cross the central/eastern states into Fri-Sat with fairly broad coverage of highs 10-20F below normal and perhaps localized colder pockets that could produce a few record values. Then by Sun-Tue the next cold surge with highs 10-25F below normal will again envelop the central and eastern U.S. and produce some more local record values. Strong high pressure and sufficiently cold air behind the lead front may bring potential for some wintry precipitation into portions of the northeastern U.S. where amounts will be focused by coastal/offshore low development by Fri. WPC Winter Weather Outlook graphics depict the upward trending probabilistic aspect of the forecast. Elsewhere, clipper systems and trailing cold cyclonic flow will bring periods of precipitation (mostly snow) to the Great Lakes/Northeast with activity prolonged by lake effect. Locations along the eastern slopes of the northern-central Rockies may see a period of snow as a front digs southward. Schichtel/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