Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
127 PM EST Thu Nov 28 2019
Valid 12Z Sun Dec 01 2019 - 12Z Thu Dec 05 2019
...Major Winter Storm will intensify over the Northeast Sunday
night into Tuesday...
...Pattern overview and Guidance/Predictability Assessment...
The medium range period (late Sunday through Thursday) begins with
the deep cold core low over the southern Great Lakes. The low
levels of this storm will be weakening/filling over the Midwest,
but the mid/upper levels remain strong/cold. The surface low
refocuses to the northern Mid-Atlantic coast Sunday night with
rapid cyclogenesis then through Monday as the low stalls off the
New England coast. The attendant cold front sweeps across the
Mid-Atlantic and Southeast through Sunday night.
The 00Z CMC remained an outlier as the fastest global guidance
with this low and was thus greatly limited in the model blend.
Otherwise there was excellent agreement among global deterministic
guidance with the track of this low through Day 4. Differences
remain with the timing of the low tracking through the Canadian
Maritimes Tuesday night/Wednesday with the 06Z GFS a little slower
than the rest of the deterministic guidance as well as the 06Z
GEFS mean. Therefore, emphasis toward the ensemble means begins on
Day 5.
Meanwhile, an upper level low shifting south off the Northwest
coast Sunday will remain off California through Tuesday/Day 5
before shifting inland sometime on Wednesday. The 00Z CMC is an
outlier here too with a track much farther west. A non-CMC blend
worked well through Day 5 with a focus on the ensemble means for
the eastward ejection for Day 6/7 which are slower than the 00Z
operational ECMWF.
...Weather Highlights/Threats...
The major winter storm to start the period over the Upper Midwest
will be weakening as its comma head precipitation shield crosses
the Great Lakes. However, rapid low development off the southern
New England coast Sunday night will refocus heavy wintry
precipitation over much of the interior Northeast. A deformation
band the tracks up interior New England Monday with some
precipitation continuing Monday night as the upper portions of the
storm pivots northeast/takes on a more negative tilt as further
shortwave activity wraps around. Strong winds will accompany this
storm over the Great Lakes and over the Northeast, making for
difficult and hazardous travel across much of the region. Behind
the cold front temperatures across the Southeast and up the
Eastern Seaboard look to be 10 to 15 degrees below normal Monday
and Tuesday before moderating through the midweek as a ridge
builds in behind the low.
In the West, another round of heavy precipitation affects central
and northern California into Monday with heavy mountain snows
expected and the heaviest rain along the coast. Locally heavy rain
and mountain snow may also shift into Southern California and
parts of the Southwest Tuesday night/Wednesday depending on when
and how the low ejects east. A chilly Sunday across the interior
West is expected under high pressure with temperatures generally
15 degrees below normal. Temperatures then moderate over The West
except for over the Great Basin where high pressure lingers until
the low shifts inland on Day 6/7.
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 rain across portions of California, Sun-Mon, Dec 1-Dec 2.
- Heavy snow across portions of the Northeast, the Central Great
Basin, the Mid-Atlantic,
California, the Upper Mississippi Valley, the Central
Appalachians, the Great Lakes, and the
Southwest, Sun-Mon, Dec 1-Dec 2.
- 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 Central Plains, the Lower
Mississippi Valley, the Northern
Plains, the Great Lakes, the Middle Mississippi Valley, the Upper
Mississippi Valley, the Southern
Plains, and the Ohio Valley, Sun, Dec 1.
- High winds across portions of the Northeast, Sun-Mon, Dec 1-Dec
2.
- Much below normal temperatures over parts of the Central Great
Basin, Sun, Dec 1.
- High significant wave heights for coastal portions of the Great
Lakes and the Upper Mississippi
Valley, Sun, Dec 1.
- High significant wave heights for coastal portions of the
Northeast, Sun-Mon, Dec 1-Dec 2.
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