Extended Forecast Discussion NWS Weather Prediction Center College Park MD 339 PM 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 across the central and eastern U.S... ...Pattern Overview and Guidance/Predictability Assessment... The synoptic pattern at the beginning of the medium range period (12Z Friday) is expected to be amplified featuring western U.S./Alaska ridge and downstream troughing over the central/eastern CONUS. Overall, forecast confidence in the large scale pattern is above average; however, confidence in details, particularly across the Northeast U.S. with respect to a coastal storm and its sensible weather impacts are lower. The GFS continues to be the more progressive/faster solution, with its surface low more offshore while the ECMWF offers a trough axis that is centered more over the eastern Great Lakes, allowing the low to track further to the coast. For this cycle, the WPC preference was mostly a blend of the deterministic GFS and ECMWF with inclusion of the GEFS/ECENS means for Day 3-4. Beyond that time frame, there is increasing signal for further amplification of the large scale pattern over the CONUS with a fairly anomalous trough developing over the east-central U.S. by early next week (and ridging remaining in place over the western U.S.). For these periods, a GEFS/ECENS blend was favored; however, teleconnections suggest ridging is likely to be more pronounced than what the ECENS mean suggests, so there was a higher weight of the GEFS mean incorporated by Day 6-7. The most recent surface progs show potential low development offshore the East Coast, although there is considerable uncertainty in its proximity to the coast and potential impacts. ...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/Taylor 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 Hazards: - Heavy snow across interior northern New England, Fri, Nov 8. - Heavy precipitation across coastal northern New England, Fri, Nov 8 and Tue, Nov 12. - Heavy snow across portions of the central Great Lakes, Tue, Nov 12. - Heavy rain across portions of the southern Plains, Tue, Nov 12. - Much below normal temperatures across much of the eastern two-thirds of the U.S., Fri-Tue, Nov 8-Nov 12. - Much below normal temperatures across portions of the Southeast, the lower Mississippi Valley, and the southern Plains, Fri-Sat, Nov 8-Nov 9. - Much below normal temperatures across portions of the northern and central Plains, and into the northern Rockies, Sun-Tue, Nov 10-Nov 12. - Much below normal temperatures across portions of the Northeast, Mon-Tue, Nov 11-Nov 12. 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