Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
510 PM EDT Tue Oct 08 2019
Valid 12Z Fri Oct 11 2019 - 12Z Tue Oct 15 2019
...Gradual moderation of record cold over parts of the
West/Northern Plains...
...Blizzard conditions possible late this week over portions of
the Northern Plains...
...Pattern Overview and Guidance/Uncertainty Assessment...
The most dominant feature during the period will be a an
anomalously deep upper low that should be strongest around early
day 4 Sat as it tracks over northern Minnesota. The upper low
will support a period of heavy snow and strong winds over some
northern tier locations and make only gradual northeastward
progress into southern Canada over the following days. Pacific
flow will bring one shortwave to the Pacific Northwest by the
start of the weekend and then the central U.S. early next week,
followed by another shortwave that could approach the Northwest
around day 7 Tue. Meanwhile a potential subtropical system could
track just off the East Coast and could bring wind/wave effects to
some areas along and offshore the New England and Mid-Atlantic
coasts before lifting away during the latter half of the period.
The National Hurricane Center is monitoring this area for
development. Please reference their outlooks for more information.
Broadly speaking an operational model blend represented consensus
well early-mid period, followed by at least half ensemble mean
input toward days 6-7 Mon-Tue. Versus the 00Z run, the 06Z GFS
compared much better to other guidance for the system off the East
Coast. On the other hand the 06Z GFS seemed a little fast with
height falls ahead of the central U.S. trough extending from the
deep northern tier storm. One other forecast consideration was
that 00Z-06Z GFS runs were stronger than other guidance with upper
troughing off California and northwestern Mexico by days 5-6
Sun-Mon. This ultimately led the GFS to bring a potential eastern
Pacific tropical system and its associated moisture farther
northeast than other solutions (including the GEFS mean).
...Weather Highlights/Threats...
The deep northern tier storm should bring the best potential for
the combination of strong winds and heavy snow to parts of the
Dakotas and western Minnesota late this week. Rainfall of varying
intensity will accompany the trailing front from the Great Lakes
into the Lower Mississippi Valley/southern Plains. The rain will
become lighter and more scattered as the front heads into the
East. Northern tier/Great Lakes precipitation should persist for
a while as moisture wraps around the slow moving system. Effects
of the western Atlantic storm over New England and coastal
Mid-Atlantic from Fri into the weekend will be sensitive to the
storm's exact track and strength. Currently expect at least some
rain to reach eastern New England with the potential for a fairly
sharp gradient. A period of strong winds will also be possible
along/offshore the coast. Toward next Tue there may be an
increase of southern tier rainfall aided by focus along a
returning Gulf Coast front and a cold front approaching from the
Plains. How much if any eastern Pacific tropical moisture becomes
involved is a major uncertainty at this time, with most guidance
suggesting less than depicted by GFS runs. Expect the Pacific
Northwest to see a period of mostly light precipitation this
weekend with a wavy front crossing the region. Another area of
moisture may approach/reach the area by next Tue.
The amplified pattern bringing record cold to parts of the West
and Plains should gradually moderate, with decreasing coverage of
much below normal temperatures. However this moderation will be
relative over the northern Plains where some highs may be more
than 30F below normal this Fri and "only" 10-25F below normal by
next Mon-Tue. Above normal temperatures will precede the cold
front that crosses the eastern half of the lower 48 Fri into Sun,
with modestly above normal readings persisting over Southeast
through early 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 Lower Mississippi Valley and
the Pacific Northwest, Tue, Oct 15.
- Heavy rain across portions of the Northeast, Fri-Sat, Oct 11-Oct
12.
- Heavy snow across portions of the Upper Mississippi Valley and
the Northern Plains, Fri-Sun, Oct 11-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 Northern/Central Plains, the
Northeast, and the Upper Mississippi Valley, Fri-Sat, Oct 11-Oct
12.
- High winds across portions of the Great Lakes, Sat-Sun, Oct
12-Oct 13.
- Much below normal temperatures across portions of the Plains,
the Northern/Central Rockies, the Great Basin, the Upper/Middle
Mississippi Valley, California, the Pacific Northwest, and the
Southwest, Fri-Sat, Oct 11-Oct 12.S
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