Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
410 PM EDT Fri Oct 11 2019
Valid 12Z Mon Oct 14 2019 - 12Z Fri Oct 18 2019
...Pattern Overview and Guidance/Uncertainty Assessment...
A deep upper low initially just north of the Great Lakes region
Monday will weaken and lift northward across eastern Canada. A
progressive shortwave coming out of the Canadian Rockies will
sweep into the northern Plains and Upper Midwest Tuesday, pushing
a cold front through the region and eventually spawn a low
pressure system over the Great Lakes Wednesday. This system will
reinforce troughing over the central/eastern US and push a strong
cold front well south into portions of Florida by late next week.
Across the west, persistent low pressure off British Columbia will
bring a parade of cold fronts into the Pacific Northwest, keeping
relatively active weather in place for much of the extended
forecast period.
Average to slightly above average forecast confidence early in the
forecast period (Day 3/4 - Mon/Tue) resulted in a preferred blend
of primarily global deterministic models. However, by Day 5
through Day 7, forecast confidence drops considerably as the
evolution of the upper level pattern across the Pacific Northwest
into the northern Plains becomes less certain. The 00Z and 06Z GFS
was much faster pushing shortwave energy across the CONUS and
closing off over the northern Plains, compared to the rest of the
guidance. The ECMWF/CMC/UKMET solutions are slower, holding back
energy off the Pacific Northwest coast, and this scenario is
preferred at this time. The forecast was leaned heavily on the
ECMWF and ECENS/NAEFS means by Day 6-7 given a solution that fit
reasonably well within the ensemble consensus.
...Weather Highlights/Threats...
A weakening/stalled frontal boundary lingering over the Lower
Mississippi Valley to Southeast Mon-Tue will be the focus for
widespread showers and thunderstorms. Model consensus suggests
that 2-3 inches of rain may be possible across portions of these
areas Mon-Tue. As the area of low pressure develops mid-week over
the Great Lakes and moves into the Northeast U.S., deeper moisture
will be pulled northward and result in widespread rainfall. Some
of this could be locally heavy. 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/Taylor
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 California, the Pacific Northwest,
and the Northern Great Basin, Tue-Fri, Oct 15-Oct 18.
- Heavy rain across portions of the Lower Mississippi Valley, the
Tennessee Valley, the Southern Mid-Atlantic, the Southern
Appalachians, the Southeast, and the Southern Plains, Mon-Tue, Oct
14-Oct 15.
- Heavy rain across portions of the Northeast, Wed-Thu, Oct 16-Oct
17.
- Flooding possible across portions of the Southeast, the
Upper/Middle Mississippi Valley, the Great Lakes, and the Northern
Plains.
- Flooding occurring or imminent across portions of the
Northern/Central Plains, the Upper/Middle Mississippi Valley, and
the Great Lakes.
- Flooding likely across portions of the Middle/Lower Mississippi
Valley, and the Southern Plains.
- Much below normal temperatures across portions of the
Northern/Central Plains, and the Upper Mississippi Valley,
Mon-Wed, Oct 14-Oct 16.
- High significant wave heights for coastal portions of the
Pacific Northwest, Thu-Fri, Oct 17-Oct 18.
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