Extended Forecast Discussion NWS Weather Prediction Center College Park MD 145 AM EST Thu Nov 28 2019 Valid 12Z Sun Dec 01 2019 - 12Z Thu Dec 05 2019 ...Major Winter Storm will track from the Upper Midwest to the Northeast Sunday and Monday... ...Pattern overview and Guidance/Predictability Assessment... The medium range period (Sunday-Thursday) begins with a developed low pressure system over the Upper Midwest/Great lakes region with an attendant cold front sweeping through the Mid-Atlantic and Southeast. Additional southern stream energy rounding the base of the associated cold core upper low should allow for the development of a new surface low off the Mid-Atlantic coast late Sunday, which then tracks up the New England coast through Tuesday. Models and ensembles show fairly good agreement on this system, though the latest run of the CMC is slightly faster than the remaining deterministic models with the track of the upper low. There are some minor differences regarding how quickly the surface low exits the New England coast as well, which of course would have implications for precipitation along the coast. The GFS is a tad slower with its exit than the ECMWF, but the means are roughly in the middle. Meanwhile, an upper level low off the Northwest coast should drop southward off the West coast through about Tuesday before a weakened state of the system begins to shift inland across the Southwest Wednesday and Thursday. Days 3-5 the deterministic models show relatively good agreement with this system, with timing differences arising by day 6 with how quickly the energy moves inland. The last few runs of the GFS and the latest run of the CMC are notably faster than the ECMWF. The means are understandably quite weak and washed out by day 7 with the shortwave, though it seems they would favor a slower shortwave closer to the ECMWF. For both systems of note, the forecast blend for days 3-5 was based mostly on the ECMWF and GFS, with small contributions from the UKMET on day 3 and the ECENS/GEFS means on days 4 and 5. Beyond that, leaned more on the means mainly due to continued uncertainty with the upper low/trough in the West. This maintains good continuity with the previous WPC forecast. ...Weather Highlights/Threats... The major winter storm to start the period over the Upper Midwest will continue spreading heavy and potentially significant accumulating snow across the Upper Great Lakes and the interior Northeast on Sunday, and into New England on Monday. High winds may also accompany this storm, making for difficult and hazardous travel across much of the region. To the south, locally heavy rainfall is possible along the attendant cold front as it shifts through the Mid-Atlantic and the Southeast on Sunday. Behind the cold front temperatures should trend cooler up and down the East Coast through Tuesday, with a moderation back towards normal by Wednesday and Thursday. In the West, another round of heavy precipitation affects California through Monday with heavy mountain snows expected in northern and central California, and rain in the lower elevations. Locally heavy rain and mountain snow may also shift into Southern California and parts of the Southwest next week as well. A chilly start on Sunday in the West should warm through the period, with temperature anomalies Monday-Thursday generally less than 10 degrees below normal. Santorelli 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