Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
153 PM EST Mon Jan 06 2020
Valid 12Z Thu Jan 09 2020 - 12Z Mon Jan 13 2020
...Heavy Rain Threat from the Lower-Mid Mississippi Valley into
Tennessee/Ohio Valleys Fri-Sat with potential for wintry
precipitation across northern Ohio Valley into New England...
...Active pattern over the Northwest...
...Overview/Guidance Assessment...
There are embedded details that exhibit some spread and
variability but guidance agrees that strong ridges aloft over the
east-central Pacific and off the southeastern U.S. coast will hold
in place an amplified western U.S. trough at least into early next
week. Within this pattern, low level flow of Gulf moisture ahead
of an ejecting western shortwave/leading wavy cold front will
produce an episode of heavy rainfall from parts of the Lower-Mid
Mississippi Valley eastward/northeastward from late this week into
the weekend with some wintry weather on the northern side of the
precipitation shield. Meanwhile energy flowing around the
northeastern side of the Pacific ridge will bring a series of
systems into the Northwest. The trajectory of moisture across the
Northeast Pacific is not favorable for extreme precipitation
totals but the accumulations over several days may still be
significant.
The first shortwave ejects from the West into the Southern Plains
Day 3-4. Operational models and ensemble means show very good
agreement on timing of this shortwave and general progression of
the low center/frontal boundary. The UKMET was a bit faster/north
than the better consensus and the means and was not included in
the blend. After day 4, the GFS and ECENS mean were slightly
faster as the shortwave lifts into the Ohio Valley compared to the
ECMWF/CMC/GEFS mean solutions, but not enough to reject it
entirely.
Upstream, the next system drops into the Western U.S. this
weekend. The GFS/ECMWF and their ensemble means show fairly good
agreement for timing of this system, with the CMC notably faster.
The energy moves out into the Plains by day 6-7 and there remain
some more timing/detail differences with the energy as it moves
from the Plains into the Midwest amongst the operational guidance.
The ensemble means show much better agreement and thus were leaned
more heavily on for the day 6-7 forecast.
The day shift WPC progs used a 100% deterministic model blend
(mostly GFS/ECMWF with some CMC) for days 3 and 4, steadily
increasing contributions from the ECENS/GEFS means days 5-7. The
CMC was removed completely after day 5 due to reasoning above.
This maintains very good continuity from the previous/overnight
WPC forecast.
...Weather Highlights/Threats...
Confidence is still above average for the overall heavy rainfall
event expected from parts of the Mid-Lower Mississippi Valley into
the Ohio/Tennessee Valleys during the late week into weekend time
frame. However uncertainty with the timing of supporting dynamics
ejecting from the West provides some challenge for resolving the
rainfall duration and highest totals. The scenario continues to be
favorable with a feed of Gulf moisture interacting with an
approaching wavy front, producing areas of heavy rain/embedded
convection. The latest WPC QPF shows a widespread area of 3-5"
with locally higher amounts from Arkansas to the Ohio Valley and
into parts of southwest New York. The Storm Prediction Center is
also highlighting a potential for severe weather across the
southern tier of states with this event for Friday and Saturday.
Meanwhile over the past day the signal for wintry precipitation on
the northern periphery of the moisture shield has strengthened.
Primary snow potential should extend from parts of the Midwest
through the Great Lakes and Northeast. The wavy cold front will
eventually cross the East Coast and extend into the Gulf. This
trailing part of the front is likely to return north as a warm
front around the start of next week and become one focus for
another potential rainfall event near the end of the medium range
period and beyond. This second event may be just to the south of
the first event from roughly Mississippi to Tennessee
Valley/Southern Appalachians. Some locations within the heavy
rainfall threat area have recently received significant rainfall
so effects from this upcoming event will require close monitoring
for flash flood and river flood potential.
The series of systems coming into the Northwest will focus the
highest rain/mountain snow totals over the Pacific Northwest
coast/northwest corner of California along with the Cascades.
Expect a secondary maximum over the northern Rockies. At times
moisture will extend southeastward into the Sierra Nevada/Great
Basin/Central Rockies but with lighter amounts in most cases.
Amounts should not be extreme given that northwesterly flow should
promote only modest anomalies for deep moisture, but multi-day
totals over the most favored terrain could reach a few inches
liquid.
From late week into the weekend expect a surge of very warm air to
extend from the central through eastern U.S. with a broad area of
plus 10-25F anomalies for highs and plus 20-30F and locally higher
anomalies for morning lows. Daily records are possible, especially
for warm lows. Most of the West will see moderately below normal
highs through the period. The extreme northern Plains/Montana will
be a focus for some colder anomalies, including some readings
20-30F below normal Sun-Mon.
Santorelli/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
- Heavy precipitation across portions of California, the Pacific
Northwest, and the Northern Great Basin, Fri-Mon, Jan 10-Jan 13.
- Heavy precipitation across portions of the Northeast, the
Central Appalachians, the Middle Mississippi Valley, the
Mid-Atlantic, the Great Lakes, and the Ohio Valley, Sat-Mon, Jan
11-Jan 13.
- Heavy rain across portions of the Mid-Atlantic, the Lower
Mississippi Valley, the Central Appalachians, the Tennessee
Valley, the Great Lakes, the Middle Mississippi Valley, the
Northeast, the Southern Appalachians, the Southeast, the Southern
Plains, and the Ohio Valley, Thu-Sun, Jan 9-Jan 12.
- Heavy rain across portions of the Lower Mississippi Valley, the
Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the
Southeast, and the Ohio Valley, Mon, Jan 13.
- Heavy snow across portions of the Northern Rockies and the
Northern Great Basin, Sat-Mon, Jan 11-Jan 13.
- Severe weather across portions of the Lower Mississippi Valley
and the Southern Plains, Fri, Jan 10.
- Severe weather across portions of the Southeast, the Lower
Mississippi Valley, the Southern Appalachians, and the Tennessee
Valley, Sat, Jan 11.
- Flooding occurring or imminent across portions of the Lower
Mississippi Valley, the Northern Plains, and the Tennessee Valley.
- Flooding likely across portions of the Pacific Northwest.
- Much below normal temperatures across portions of the Northern
Plains, the Northern Rockies, and the Northern Great Basin,
Sun-Mon, Jan 12-Jan 13.
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