Extended Forecast Discussion NWS Weather Prediction Center College Park MD 144 PM EST Fri Nov 29 2019 Valid 12Z Mon Dec 02 2019 - 12Z Fri Dec 06 2019 ...Significant winter storm to affect the Northeast into Tuesday... ...Low pressure brings midweek heavy rain to southern California... ...Pattern Overview and Guidance/Predictability Assessment... A cold core mid/upper low with neutrally tilted trough over the Southeast over the Mid-Atlantic Monday morning will become negatively tilted as it slowly tracks northeast along the Northeastern seaboard through Tuesday. The surface low is expected to track just off Cape Cod Monday night and across Nova Scotia Tuesday. Meaningful winter weather effects are expected to the north/west of the low track. There is excellent agreement among deterministic guidance with this low to allow a general deterministic model blend through its exit on Tuesday/Day 4. The next trough tracks southeast across the Great Lakes Tuesday night and across the northeast through Wednesday night. Surface low pressure developing offshore looks to track just east of Maine Wednesday night which is in decent agreement in the 06Z GFS and 00Z ECWMF. Meanwhile an upper low in a positively tilted trough lingers off California through Tuesday. Timing of the ejection east across southern CA is in better timing agreement with the low/trough axis crossing on Wednesday. This trough then shifts east across the southern tier of the CONUS through Friday. Timing differences increase as this feature moves inland with the 06Z GFS outpacing the 06Z GEFS which is similar to the 00Z ECMWF/ECENS. An upstream trough is expected to amplify over the eastern Pacific late in the week. The 00Z ECMWF/ECENS farther west/more positively tilted than the 06Z GFS/GEFS which has been common this month for systems along/off the West Coast. Precipitation may arrive into much of the West Coast on Day 7 per a 06Z GEFS/00z ECENS blend for that day. The model blend preferences were for a general deterministic model blend weighted toward the 06Z GFS/00Z ECMWF for Days 3/4 with increasing 06Z GEFS/00Z ECENS weight Day 5-7. ...Weather Highlights/Threats... The cold core low tracking up the Northeast Monday into Tuesday will bring a period of significant wintry precipitation in a swath from the northern Mid-Atlantic, the Hudson Valley, south-central New England, and eastern Maine. Winds look to be sufficiently strong to make travel even more difficult/hazardous. The Great Lakes should expect to see a period of mainly light snow in the Wednesday timeframe as the trough crosses with preferred lake effect zones of Erie and Ontario likely having the most notable threat. The system moving into the Southwest will bring an episode of focused precipitation with highest totals most likely over favored terrain inland from the southern California coast Tuesday night through Wednesday with a lesser maximum over central Arizona later Wednesday. High elevation snow likely from the Sierra Nevada across the ranges of the Great Basin to the central Rockies. This system would produce an area of mostly rain over and east of the central-southern Plains into the Southeast Thursday/Friday. Timing and exact focus of potentially heavy precipitation on the West Coast is sensitive to lower predictability details with the trough. Currently the best potential for highest totals remains over northern California for Day 7. The eastern states will be chilly to start the week in the wake of the coast-to-coast storm with much of the Southeast temperatures 10 to 15F below normal Monday. Those anomalies spread to Florida for Monday night/Tuesday with freezes possible into the northern Peninsula. Eastern U.S. temperatures will gravitate toward normal by the latter half of the week. On the other hand expect the central U.S. to see above normal temperatures for most of the period with some pockets of plus 10F or greater anomalies for min and/or max readings from Tue onward. The expected pattern will support continued moderately below normal highs over the Great Basin and at times into southern California while most of the West should see morning lows closer to or above normal. Jackson 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 precipitation across portions of California, the Central Great Basin, the Pacific Northwest, and the Southwest, Mon, Dec 2 and Fri, Dec 6. - Heavy rain across portions of California, Wed, Dec 4. - Heavy snow across portions of the Mid-Atlantic and the Northeast, Mon-Tue, Dec 2-Dec 3. - Flooding possible across portions of the Northern Plains. - Flooding occurring or imminent across portions of the Northern Plains. - Flooding likely across portions of the Northern Plains and the Southwest. - High winds across portions of the Northeast, Mon-Tue, Dec 2-Dec 3. - Much below normal temperatures across portions of the Southeast and the Lower Mississippi Valley, Tue, Dec 3. 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