Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1218 PM EST Sat Nov 30 2019 Valid 12Z Tue Dec 03 2019 - 12Z Sat Dec 07 2019 ...Winter storm shifts from New England Tuesday... ...Low pressure brings midweek heavy rain risk to southern California... ...Pattern Overview and Guidance/Predictability Assessment... Overnight guidance is in decent agreement for the multi-day long wave pattern across North America through the next week with general troughing in the northeast US and troughing off/along the West Coast and a deep Arctic low over the Canadian Archipelago. However, the two troughs are transient and detail/timing uncertainties remain through the Day 3-7 timeframe. The strong low that crossed the country since Thursday departs New England Tuesday. Troughing across the northeast CONUS then comes from a northwest jet from the Canadian Prairies on the south side of the sprawling Arctic low centered north of Hudson Bay. The first trough in this pattern reaches the Northeast Wednesday by way of the Great Lakes. This trough takes on a negative tilt Wednesday night with the resultant low and potential heavy precipitation well east of New England. Further shortwave troughs and impulses then track into the northeast CONUS/Great Lakes through the rest of the week. Farther west an upper trough/closed low off California will eject east and into southern California Tuesday night/Wednesday, weakening as it passes through the longer term mean ridge and further shearing downstream as it becomes increasingly embedded in progressive flow as it crosses the southern tier of the CONUS. An upstream trough will amplify into the eastern Pacific mid-late week with its axis likely affecting the West Coast next weekend. The trough entering the Southwest midweek is the main weather maker for the CONUS through the medium range period. The GFS continues to be the fastest and the ECMWF the slowest. However, the 06Z GEFS and 00Z ECENS means were in decent agreement with this feature through the forecast period in terms of heights and precipitation. Therefore the blend was uncharacteristically heavy on these two ensemble means (at least compared to this past week) through Days 3 to 7. ...Weather Highlights/Threats... Wrap around snow looks to lift north from Maine Tuesday. The next shortwave trough crosses the Great Lakes Tuesday night into Wednesday with the following northwest flow promoting lake effect snow off, particularly off Erie and Ontario Wednesday/Wednesday night. The system moving into the Southwest Tuesday night/Wednesday midweek should produce a brief period of enhanced rain and mountain snow with highest totals over favored terrain inland from the southern California coast and then a lesser maximum over central Arizona. High elevation snow is possible from the Sierra Nevada across the ranges of the Great Basin to the central Rockies. Expect this system to produce an area of mostly rain over and east of the central-southern Plains into the Southeast late in the week. Some pockets of locally moderate-heavy rain are possible but with low confidence in timing/location. Late in the period guidance is maintaining the signal for potentially heavy precipitation (rain and higher elevation snow) along parts of the West Coast with strongest focus over northern California and the Sierra Nevada. Differences exhibited by the models/ensemble means continue to suggest more uncertainty with the onset of the event rather than the event itself. Below normal temperatures will persist over parts along the Eastern Seaboard and the Southeast into Wednesday with anomalies of 10 to 15 degrees below normal for Florida. Morning lows could drop to near freezing as far south as far northern Florida peninsula on Tuesday. Eastern U.S. temperatures should be closer to normal late in the week but another frontal passage may push highs back down to 5 to 10 degrees below normal over the Mid-Atlantic/Northeast next Sat. Expect the central U.S. to see above normal temperatures on most days, more so for morning lows except under surface high pressure that has a decent signal for Friday over the northern Plains and Saturday over the Midwest. The warmest anomalies should be over the northern Plains Tuesday and Wednesday ahead of a cold front and across the southern tier Wednesday to Friday with clouds/precip accompanying the system crossing the region. Highs about 5 to 10 degrees below normal should persist over the Great Basin into parts of Arizona/southern California while most of The West should see near to above normal morning lows. 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 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