Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
355 PM EST Thu Dec 12 2019
Valid 12Z Sun Dec 15 2019 - 12Z Thu Dec 19 2019
...Winter weather threat over the central Plains Sun/Mon may move
to the East Coast by midweek, with heavy rainfall likely across
the south...
...Pattern Overview and Guidance/Predictability Assessment...
Broad troughing to start the period (Sunday) will shift focus to
the shortwave ejecting out of the Four Corners region and through
the southern/central Plains. This system will slide
east-northeastward to the Mid-Atlantic by Tuesday and then out to
sea. Another Pacific system will stumble into California Wed/Thu.
A main surface low will track quickly to the east/northeast from
the Southern Plains Sun/Mon into the Mid-Atlantic and Northeast by
Tuesday. There remains some question on the exact track of this
system with the latest run of the ECMWF (12/00z) farther east than
the other deterministics and many of the ensemble members. The
GFS/UKMET/CMC are all a bit slower/farther west with the low, but
the ensemble means tend to cluster somewhere in the middle. Thus,
a kind of middle ground solution (maybe a bit closer to the GFS
camp though) was preferred for this system which also maintains
good continuity with the previous forecast. In the West, the
GFS/ECMWF were fairly close with the trough approaching the coast
which is also in line with the ensembles. However, the GFS
continued to be flatter with its downstream ridge into the Four
Corners next Wednesday. With uncertainty in how the stretched
western system evolves, coupled with the amount of cold air across
the Upper Midwest mid to late next week, a trend towards a bit
more ensemble weighting was preferred for the end of the period.
...Weather Highlights/Threats...
An initial wrapped-up surface low over northern Maine on Sunday
will move into the Canadian Maritimes on Monday with high pressure
in its wake which should bring in cooler air (20s/30s) to the
Northeast. Over the Plains, as low pressure exits the Foothills it
will spread rain (south) and snow (north) over the area. There
remains some north-south spread in amounts and precipitation type
(depending on the track of the low in relation to the
colder/warmer air mass interface) but a swath of at least plowable
snow seems fairly likely over parts of Kansas. Winter weather
outlook probabilities 30-50% encompassed most of the Sunflower
State Sun-Mon. As the area of low pressure moves eastward, rain
may expand and increase over the Southeast from the Lower MS
Valley to the TN Valley and southern Appalachians. To the north,
snow is possible on the northern side of the precipitation shield
across the Ohio Valley and interior Mid-Atlantic, but this is
highly dependent on the eventual track of the surface low. To the
West, precipitation with the incoming Pacific front will focus
along the coast and into the Sierra.
Santorelli/Fracasso
Hazards:
- Heavy precipitation across portions of the Northeast, the
Central Appalachians, the Mid-Atlantic, and the Ohio Valley,
Mon-Tue, Dec 16-Dec 17.
- Heavy precipitation across portions of western Washington, Thu,
Dec 19.
- Heavy precipitation across portions of northern California and
western Oregon, Thu, Dec 19.
- Heavy rain across portions of the Lower Mississippi Valley, the
Tennessee Valley, the Southern Appalachians, and the Southeast,
Mon-Tue, Dec 16-Dec 17.
- Severe thunderstorms across portions of the Middle and Lower
Mississippi River Valley, Mon, Dec 16.
- Heavy snow across portions of the Central Rockies, Sun, Dec 15.
- Heavy snow across portions of the Central Plains, Sun, Dec 15.
- Heavy snow across portions of the Northeast, Mon-Tue, Dec 16-17.
- Flooding occurring or imminent across portions of the Northern
Plains.
- Flooding likely across portions of the Northern Plains.
- High winds across portions of the Northeast, Sun, Dec 15.
- Much below normal temperatures across portions of the Upper
Mississippi Valley and the Northern Plains, Sun, Dec 15.
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