Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
136 AM EST Fri Nov 15 2019
Valid 12Z Mon Nov 18 2019 - 12Z Fri Nov 22 2019
...Pattern Overview and Guidance/Predictability Assessment...
During the medium range, relatively amplified and progressive flow
from the North Pacific into Canada and the CONUS northern tier
will be flanked to the south by a somewhat less progressive
southern stream with a tendency for upper-level energy to close
off and move a bit more slowly. The ECMWF and GFS showed slightly
above average agreement through the medium range, although both
have shown some degree of variability over the past several runs,
so any consensus is at least somewhat tenuous. Two low pressure
systems are forecast to track northward off the Eastern Seaboard,
the first on Mon and the second Tue-Wed. ECMWF and GFS solutions
showed some timing and intensity differences for these systems,
but the solutions were close enough to be used in a blend. Farther
west, shortwave energy diving south along the West Coast Mon
night/Tue is forecast by the ECMWF/GFS and numerous ensemble
members to close off across the Southwest by late Wed, perhaps at
least partially interacting with upper-level energy associated
with what is now Tropical Depression Twenty-E over the eastern
Pacific. Model/ensemble solutions show general consensus that this
closed upper low should rather slowly move east across the Four
Corners region and southern Rockies by Fri, perhaps reaching the
Southern/Central Plains. At the same time, northern stream
shortwave energy is expected to amplify across the Great Lakes,
pushing a cold front across much of the central U.S.
The WPC surface progs were based on a blend of the 12Z ECMWF/18Z
GFS as well as the 18Z GEFS mean, along with a substantial
weighting of forecast continuity through day 6 (availability of
ensemble and some deterministic model data was limited due to
network issues during model ingest times).
...Weather Highlights/Threats...
Initially chilly temperatures across the eastern third of the
nation on Mon, should moderate toward normal by the middle of next
week. On the other hand areas from the West into parts of the
northern-central Plains will see well above normal temperatures
(up to plus 10-20F anomalies), especially Mon-Tue.
The lead system off the Mid-Atlantic coast should keep the
heaviest rains offshore but could be close enough to produce some
rain along the coast. If any moisture extends farther inland it is
most likely to be over the Northeast. In that case the western
periphery of the moisture shield could contain some snow. The
strong pressure gradient between the low and the surface high
exiting New England will lead to windy conditions along the coast
and especially over the nearshore waters. Please see the Ocean
Prediction Center's products for more information. Precipitation
coverage and intensity with the second area of low pressure
evolving Tue-Thu are more uncertain, with the Northeast again the
most likely area to see some rain and inland/higher elevation snow
if the moisture shield extends far enough westward.
Favored terrain in the Pacific Northwest/northern Rockies will an
episode of light-moderate precipitation Mon-Tue. The upper low
settling over or near southern California mid-late week would
increase the potential for significant precipitation (mostly rain)
over the Southwest and in particular central Arizona, especially
if additional tropical moisture associated with the eventual
remnants of Twenty-E is drawn northward. Remaining western energy
aloft progressing across the northern half of the lower 48 may
bring a front and accompanying precipitation into the east-central
U.S. by next Thu. A potential wave of low pressure along the
trailing end of the frontal boundary across the Southern/Central
Plains may bring an increase in precipitation to areas from the
Plains to the lower/mid-Mississippi Valley as well. Depending on
the intensity of the low pressure wave, sufficient moisture
advection into the cold air north of the surface front will be
possible to produce some winter weather potential from the
mid/upper-Mississippi Valley to the Great Lakes.
Ryan/Rausch
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