Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
138 PM EST Tue Nov 26 2019
Valid 12Z Fri Nov 29 2019 - 12Z Tue Dec 03 2019
...Major Winter Storm Crosses Country Thanksgiving Weekend...
...Pattern overview and Guidance/Predictability Assessment...
A deep cold core low centered over the Great Basin early Friday
shifts east across the rest of the CONUS through Monday,
potentially lingering near New England through Tuesday. Shortwave
energy rounding the base of the low ejects northeast from the
Desert SW Friday, reaching the north-central Plains Friday
evening. Surface low pressure develops in the lee of the CO
Rockies Friday and rapidly strengthens as it shifts northeast to
South Dakota Friday night. The shortwave energy wraps into the
parent low over South Dakota Saturday with the system turning east
which reaches them crosses the southern Great Lakes before
reaching the northern Mid-Atlantic coast Sunday night. There is a
risk for further southern stream energy to wrap in with new
surface low development along the Mid-Atlantic coast up to the New
England Coast through Monday. The next low/trough approaches
shifts southeast off The West Coast this weekend with multiple
rounds of energy shifting this system south off or near the coast
through the early part of next week.
00Z/06Z deterministic guidance was in good agreement (except for
the 00Z UKMET noted below) with both systems and associated ridges
through Day 5 before timing differences on the low tracking up the
northeast coast. The 00Z UKMET remained slower with the ejection
of shortwave energy over the Desert SW on Day 3 which leads to
outlier placement of associated features and precipitation, so it
was excluded from the medium range model blend which favors the
00Z ECMWF and 06Z GFS for Days 3-5. The 06Z GFS remained farther
east/more progressive with the low off New England for Days 6/7
than the 00Z ECMWF, while the mean trough axis in the 06Z GEFS and
00Z ECENS is similar. Therefore the heaviest weight for Days 6/7
were with the ensemble guidance.
...Weather Highlights/Threats...
Widespread hazardous weather is expected as the low ejects across
the country through the Thanksgiving holiday weekend. Heavy,
rather low elevation mountain snows are expected Friday into
Saturday for much of the Central and Southern Rockies. As the
surface low moves and rapidly develops into the northern Plains, a
swath of heavy and rather significant accumulating snow is likely
north and west of the low on the Plains from eastern
Montana/northeastern Wyoming across the Dakotas to the Upper Great
Lakes through Saturday night. The focus then shifts to the
developing coastal low off the Mid-Atlantic Sunday night,
continuing up the New England coast into Tuesday. High winds look
to accompany all phases of this system making for difficult and
hazardous travel across much of the region. Along and ahead of the
attendant cold front, locally heavy rainfall is likely from the
Southern Plains/Gulf Coast to the Ohio Valley. The latest SPC
severe weather outlook has a 15 percent chance of severe weather
for Friday across the Southern Plains, shifting southeast to the
west-central Gulf coast with another 15 percent chance of severe
weather for Saturday.
Notable temperature anomalies are expected with the system
crossing the country. Cold air will focus across The West through
the weekend with daytime highs 15 to 25 degrees below normal
spreading east from the Great Basin Friday into the lee of the
Rockies Saturday. A sweeping cold front crossing the country
through Sunday night spreads below normal temperatures (generally
10 degrees or so below normal). Temperatures will be above normal
(max temperatures 10 to 15 degrees above normal) over the southern
Plains and Midwest Friday/Saturday ahead of the cold front.
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