Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
242 AM EDT Fri Oct 11 2019
Valid 12Z Mon Oct 14 2019 - 12Z Fri Oct 18 2019
...Pattern Overview and Guidance/Uncertainty Assessment...
A relatively amplified and progressive pattern will be in place
across the CONUS during the extended period. A deep upper-level
low initially in place just north of the Great Lakes on Mon is
forecast to lift northward across eastern Canada while a cold
front sweeps across the Mid-Atlantic/Northeast. Meanwhile,
shortwave energy crossing the Great Basin/Rockies on Mon and the
central U.S. on Tue is forecast to amplify across the Great Lakes
and eastern U.S. Wed/Thu, moving a relatively strong cold front
off the Eastern Seaboard. The pattern will become much more
unsettled across the Northwest by the middle of next week as a
series of shortwaves/frontal systems approach the region in rapid
succession.
The WPC medium range forecast was based initially on a multi-model
deterministic blend (including the 12Z ECMWF/UKMET/18Z GFS) on
days 3-4 (Mon-Tue). Starting on day 5 (Wed), the GFS was removed
from the blend, as it become significantly faster than the
model/ensemble consensus to lower heights across the Pacific
Northwest and farther inland. The differences only increased later
in the period, with the GFS developing a deep closed upper-level
low across the north central U.S. by days 6-7 (Thu-Fri), while the
ECMWF along with most ECENS and CMCE ensemble members keep broad
anticyclonic flow across the central U.S., and more amplified
troughing along the West Coast. Thus, the forecast during days 5-7
showed gradually increasing weight on the ECENS/NAEFS ensemble
means, with some continued weight on the ECMWF through the end of
the forecast period given a solution that fit reasonably well
within the ensemble consensus.
...Weather Highlights/Threats...
A weakening frontal boundary forecast to linger from the lower
Mississippi Valley to the Southeast days 3-4 is expected to
produce widespread showers and thunderstorms, with heavy rain
possible. Model consensus suggests that 2-3 inches of rain may be
possible across portions of these areas Mon-Tue. Farther north,
low pressure expected to move from the mid-Mississippi Valley on
Tue to the Ohio Valley/Northeast Wed/Thu is expected to gradually
draw in deeper moisture, and widespread moderate to locally heavy
rain is forecast across the Northeast Wed into Thu. Meanwhile,
precipitation is expected to gradually increase across the Pacific
Northwest starting next Tue and continuing through the end of the
week as multiple shortwaves/frontal systems affect the region.
Snow-levels are forecast to be relatively high initially, but
should begin to fall by later in the week as lower heights begin
to press inland. Regardless, heavy precipitation is expected to
become widespread across the coastal ranges of the Northwest as
well as the Cascades by later in the week, with multi-inch liquid
equivalents possible.
Temperatures are forecast to initially be well below average
across the north central U.S. in the wake of this weekend's winter
storm. Highs are forecast to be 15-25 deg F below average across
portions of the northern Plains and Upper Midwest Mon-Wed, before
temperatures moderate later in the week. Cooler temperatures are
forecast to spread into the eastern half of the nation by the
middle to end of next week as Canadian high pressure overspreads
the region behind the cold front. High temperatures 5 to 15 deg
below average are forecast across a large area from the
Mississippi River to the Eastern Seaboard.
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