Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 PM EST Wed Nov 20 2019
Valid 12Z Sat Nov 23 2019 - 12Z Wed Nov 27 2019
...Pattern Overview and Guidance/Predictability Assessment...
Models and ensemble indicate a fairly active synoptic pattern
going into the medium-range period across the U.S. Decent model
agreement is now shown regarding a developing low pressure system
moving fairly quickly across the South on Saturday and into the
Eastern Seaboard Saturday night. By Sunday morning, the system
will likely be moving off the East Coast where some additional
cyclogenesis appears likely. Nevertheless, models continue to show
a trend toward more phasing of this system with the northern
stream energy. This has resulted in a storm track that is edging
closer and closer to the New England coast Sunday into Sunday
night. The latest WPC forecast charts show the storm center
clipping Cape Cod Sunday morning before departing into the
Canadian Maritimes early on Monday.
Meanwhile, the next cold front associated with a fairly vigorous
shortwave will likely be pushing rapidly southeastward across the
western U.S. early next week. By around Tuesday of next week,
models begin to show differences in the forward motion of this
shortwave and the amount of energy ejecting into the central
Plains shortly afterward. Despite the model differences and some
expected run-to-run fluctuations in the forecast storm track and
intensity, it appears that there is a decent chance for a
significant low pressure system to form over the central Plains
then moving toward the Great Lakes region during the mid-week
period. The 06Z GEFS agrees very well with the 00Z EC mean on
this scenario. However, the 00Z GEFS was much slower in
comparison.
The WPC medium-range grids and forecast charts were derived mainly
from a blend of the 06Z GFS/GEFS and the 00Z ECMWF/EC mean
together with a small percentage of the 00Z CMC. A smaller
percentage of the deterministic 06Z GFS than usual was included
due to the presence of an anomalous shortwave trough diving south
across the northern Plains during the weekend, which looks
spurious by comparison with other models. A large percentage of
the 00Z EC mean and 06Z GEFS were used to handle the uncertainty
associated with potential central U.S. cyclone midweek next week.
...Weather Highlights/Threats...
The low pressure system crossing the eastern U.S. on Saturday is
expected to bring showers and some thunderstorms to areas from the
Southeast and southern Appalachians to the Mid-Atlantic, with
locally heavy rain possible. Greater uncertainty exists farther
north due to the variability surrounding the surface low track off
the Northeast coast. But with the model trending toward a storm
track closer to the New England coast, chance of snow and/or mixed
precipitation is now indicated for the interior sections of the
Northeast Saturday and Sunday.
For the western U.S., rain and mountain snow are expected across
the Pacific Northwest and northern Great Basin/northern Rockies
Sat-Sun as the first of the two significant shortwaves and cold
fronts move inland. The snow should linger into early next
Tuesday over the central Rockies as a low pressure system begins
to develop across the central U.S. It appears that showers and
some thunderstorms will be likely ahead of the system as they move
up the Mississippi Valley into the Ohio Valley next Tuesday and
Wednesday. On the back side of the system, there could be
potentially significant winter weather spread across the northern
Plains into the upper Midwest. Please refer to WPC Day 4-7 Winter
Weather Outlooks for specifics on the medium range winter weather
threat. Finally, as the next low pressure system reaches the
Pacific Northwest toward the middle of next week, expect a renewal
of potentially coastal heavy rain and inland snow for that region.
Expect chilly temperatures to overspread the eastern U.S. Sat-Sun,
with highs 5 to 10 deg F below average. A warming trend will
bring high temperatures 5 to 10 deg above average to the northern
Plains and Upper Midwest over the weekend. Meanwhile, as the upper
trough digs into the West by early next week, expect temperatures
to drop, with highs 5 to 15 deg below average across much of the
interior western U.S. Below average temperatures should spread
east into the central U.S. by the middle of next week behind the
cold front and the strengthening low pressure system.
Kong
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 the Central Plains, the Lower
Mississippi Valley, the Pacific Northwest, the Northern Great
Basin, the Middle Mississippi Valley, the Southern Plains, and the
Ohio Valley, Tue, Nov 26.
- Heavy rain across portions of the Lower Mississippi Valley, the
Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the
Southeast, and the Ohio Valley, Fri-Sat, Nov 22-Nov 23.
- Flooding occurring or imminent across portions of the Northern
Plains.
- Heavy precipitation across portions of the Alaska Panhandle,
Fri, Nov 22.
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