Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
334 PM EDT Wed Oct 09 2019
Valid 12Z Sat Oct 12 2019 - 12Z Wed Oct 16 2019
...Pattern Overview and Guidance/Uncertainty Assessment...
During the weekend into early next week the very deep upper low
expected to be over northern Minnesota as of early Sat should
drift slowly toward western Lake Superior and then track into
Ontario, with gradual weakening after early Sun. The upper trough
extending from the low will push a cold front through the East
during the weekend while the southern part of the front settles
near the Gulf Coast. Meanwhile shortwave energy moving into the
West during the weekend will progress eastward thereafter. This
energy will push another front across the lower 48 with possible
anchoring low pressure crossing the Midwest/Great
Lakes/southeastern Canada Mon night into Wed. Another shortwave
approaching western North America around day 6 Tue should eject
rapidly inland ahead of upstream amplifying trough energy (at
least some of it likely associated with current Super Typhoon
Hagibis).
The greatest uncertainty in the forecast involves rainfall
coverage and intensity across portions of the southern states
including the Southwest. From the southern Plains eastward
guidance diverges over how much moisture returns northward
along/north of the Gulf Coast with GFS runs tending to keep
moisture more suppressed than most other guidance--corresponding
to that model showing lower heights aloft. By mid-late period
there is also wide spread in models/ensembles for possible eastern
Pacific tropical development, with influence from differing
solutions for diffuse upper troughing that amplifies for a time
well offshore California/Mexico as well as strength of a ridge
that extends across northern Mexico. Currently the northwestward
extent of GFS moisture into the Southwest U.S. is fairly extreme
(or even an outlier) relative to other solutions including the 06Z
GEFS mean.
Aforementioned lower-confidence issues in the GFS, along with the
GFS runs possibly becoming too progressive with energy reaching
western Canada day 7 Wed plus progressive and amplified with the
eastern U.S. upper trough late in the period, favored tilting the
forecast about 70 percent toward the 00Z ECMWF/UKMET/CMC early in
the period and then the ECMWF/ECMWF mean/CMC by days 6-7 Tue-Wed
with the remaining 30 percent devoted to the 06Z GEFS mean at that
time. The GEFS mean could still be a little fast over the East
late in the period but compared well to the other means elsewhere.
...Weather Highlights/Threats...
Confidence is not particularly high yet but the best potential for
significant rainfall should extend from parts of the southern
Plains through Lower Mississippi Valley into the Tennessee Valley.
Moisture along/north of the front settling near the Gulf Coast
and then eventually lifting northward, and possibly eventual input
of moisture from the tropical eastern Pacific, should help to
enhance rainfall totals over some locations in this area. Some of
the Pacific tropical moisture could reach locations over or west
of the southern High Plains.
Elsewhere, moisture wrapping around the deep storm initially
affecting the northern tier states will be slow to depart, leading
to scattered precipitation over parts of the Upper Midwest and
Great Lakes through the weekend and into early next week. The
leading cold front should bring mostly light rain to portions of
the East on Sat. The shortwave trough/associated cold front will
bring mostly light rain/mountain snow to the Pacific Northwest and
northern Rockies from the weekend into early next week. Expect
the Pacific Northwest to see another episode of precipitation by
next Tue-Wed.
The northern Plains will continue to be the focus for coldest
temperatures relative to average. Highs should be 20-30F below
normal during the weekend with only gradual moderation to 5-20F
below normal by the middle of next week. The Upper Midwest will
be quite chilly as well with most days at least 10F below normal.
The rest of the central U.S. will see a more pronounced warming
trend after Sat, though another front will bring a cooling trend
on Wed. The East will see above normal temperatures on Sat, while
locations across the Southeast should be above normal most of the
period. Warmth will extend farther west across the southern tier
during the first part of next week.
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
Hazards:
- Heavy rain across portions of the Pacific Northwest, Wed, Oct 16.
- Heavy rain across portions of the Lower Mississippi Valley, the
Southern Plains, and the Tennessee Valley, Tue-Wed, Oct 15-Oct 16.
- Heavy snow across portions of the Upper Mississippi Valley and
the Northern Plains, Sat-Sun, Oct 12-Oct 13.
- Flooding possible across portions of 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 Northern Plains.
- High winds across portions of the Central Plains, the Upper
Mississippi Valley, and the Northern Plains, Sat-Sun, Oct 12-Oct
13.
- High winds across portions of the Great Lakes, Sun-Mon, Oct
13-Oct 14.
- Much below normal temperatures across portions of the
Northern/Central Plains, the Upper/Middle Mississippi Valley, and
the Great Lakes, Sat-Tue, Oct 12-Oct 15.
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