Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
232 AM EDT Sun Oct 13 2019
Valid 12Z Wed Oct 16 2019 - 12Z Sun Oct 20 2019
...Pattern Overview and Guidance/Uncertainty Assessment...
A relatively amplified but progressive pattern will be in place
across the CONUS during the extended period. A trough is forecast
to amplify across the Great Lakes/Northeast Wed/Thu, with a closed
upper-level low expected to develop. At the surface, a low
pressure system and surface frontal system are forecast to cross
the eastern U.S. ahead of the trough. With the initial surface low
crossing the Great Lakes on Wed, formation of a new surface low is
expected across the Mid-Atlantic region, which is forecast to
quickly intensify as it moves northeastward along the New England
coast Wed night/Thu. Farther west, an intense Pacific upper-level
jet is forecast to reach the Pacific Northwest, along with a train
of shortwave energy, starting Wed night. This should quickly lower
heights across the Northwest and eventually the northern Rockies
as the systems move inland. By Fri, the first significant
shortwave in this series should exit from the Rockies into the
central U.S., pushing a leading cold front into the Plains. Models
show this perhaps being followed by amplification of a more
significant shortwave across the Four Corners region or Rockies by
Sun, poised to move east into the Plains beyond the end of the
forecast period.
The WPC medium range forecast was initially based on a blend of
the 12Z ECMWF/GFS/CMC on days 3-4 (Wed-Thu). The 12Z GFS was
preferred over the 18Z run due to a track closer to the
model/ensemble consensus with the northeastern U.S. coastal low
during this frame. Additionally, a blend of these solutions should
smooth out timing differences with the arrival of the West Coast
trough on Thu. During days 5-7 (Fri-Sun) a gradual trend was shown
toward heavier weighting of ensemble means (ECENS/GEFS). Model
differences were largest with the potential amplification of
shortwave energy across the Four Corners region by next weekend.
In general, the trend in the guidance has been toward a slower and
more amplified system, although the 00Z GFS seemed to back off
that trend (while the CMC continued to trend slower/deeper). Thus,
model spread remains relatively high by next weekend, supporting
the heavier ensemble weighting. Consensus appears much better
across the eastern U.S., where most guidance agrees that
subtropical ridging will build off the Southeast U.S. coast,
lending to greater overall amplification of the pattern and
setting up a broad region of southerly/southwesterly flow across
the Mississippi Valley ahead of the trough.
...Weather Highlights/Threats...
Widespread and potentially heavy precipitation is expected across
the Pacific Northwest by mid to late week as the series of
shortwaves and surface fronts move inland. Snow-levels are
forecast to fall as lower height begin to press inland. The
heaviest precipitation is expected to fall across the coastal
ranges as well as the Cascades, with multi-inch liquid equivalents
possible. By next weekend, moisture return across the central U.S.
ahead of the western trough could generate scattered showers and
thunderstorms across portions of the Mississippi Valley.
Meanwhile, a lingering surface front in the Gulf of Mexico may
focus areas of showers and storms along the western/central Gulf
Coast.
Relatively cool conditions are forecast across much of the central
and eastern U.S. Wed into Thu, with highs for many areas 5 to 15
deg F below average. These temperatures should warm by Fri and
into next weekend. Meanwhile, initially above average temperatures
across much of the West (highs 5 to 10 deg above normal) will be
replaced by much cooler conditions as upper troughing moves
inland. Highs are forecast to be 5 to 10 deg below normal across
the Northwest by Thu. By next weekend, colder conditions should
overspread much of the western U.S. as the main upper trough axis
presses inland and amplified, with highs forecast to be as 15 deg
below normal for some areas.
Ryan
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