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000
FXUS02 KWBC 051915
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
215 PM EST Sun Feb 05 2023

Valid 12Z Wed Feb 08 2023 - 12Z Sun Feb 12 2023

...Guidance/Predictability Assessment...

Latest guidance continues to exhibit higher-than-normal
uncertainty for much of the medium-range period especially across
the eastern two-thirds of the country.  The medium-range period
will begin on Wednesday with the models generally agree that the
shortwave/upper low that is forecast to eject out from the
Southwest will develop into a low pressure system over the
southern Plains and track toward the northeast.  However, models
continue to show a great deal of spread regarding the timing and
amplitude of this system thereafter, with the GFS being the
fastest, the CMC being quite slow, while the ECMWF is in between
these extremes.  The subsequent evolution of this system over the
eastern U.S./East Coast later next week will be further
complicated by a simultaneous flow amplification across the U.S.,
with a much amplified ridge over the western U.S. while a large
closed low is forecast to develop somewhere near/off the West
Coast with a high degree of uncertainty on its location.  In
addition, a shortwave rapidly moving across the Pacific Northwest
on Wednesday would further complicate the pattern evolution in the
eastern U.S. late next week as the wave could positively reinforce
a surge of polar air down the Plains during the latter part of
next week, which could trigger the development of a smaller scale
low pressure system somewhere in the Mid-South late this week as
indicated by the deterministic model solutions.  This system may
then interact with residual energy on the back side of the first
system off the New England coast to form another low pressure
system near the East Coast.  By next Sunday, models generally
agree that the low pressure system(s) should begin to move away
from East Coast but the whereabouts of the upper low near/off the
West Coast remain highly uncertain.

The WPC medium range product suite through medium-range period was
primarily derived from a composite blend of 40% from the 00Z
GEFS/00Z & 06Z GFS, 40% from to 00Z ECMWF/EC mean, and 20% from
the 00Z CMC and CMC mean.  The 06Z GEFS was not included due to a
much faster northeastward track of the low from the South to the
Great Lakes.  As for the low near/off the West Coast next weekend,
a solution between the 00Z GEFS and the 00Z EC mean was adapted,
which places the system near the southern California coast by next
Sunday.  This solution is supported by the latest 12Z ECMWF with a
faster eastward motion of the system.


...Weather/Hazard Highlights...

An initially closed southern stream upper trough/low will eject
into the southern Plains by midweek as a kicker shortwave trough
digs southeastward through the Great Basin to support some
potential for snow there into the Rockies. Downstream, a surface
frontal wave over Texas with the lead system will organize, deepen
and occlude while lifting northeast into the Midwest/OH Valley
Thursday before exiting through the Northeast Friday. Gulf
moisture inflow/instability and supportive upper jet/height falls
will combine with the associated frontal system to produce a swath
of heavy rain/convection this period across the Lower/Mid MS and
TN/OH Valleys, with widespread moderate rains then shearing across
the Appalachians and Eastern Seaboard. The WPC experimental Day 4
Excessive Rainfall Outlook (ERO) will show a "marginal" threat
area over the mid MS Valley and vicinity through Wednesday, with a
noticeable northeastward shift compared with the previous
forecast. Cold air draped to the north of the system and several
potent shots of Canadian air in the wake of system passage will
also offer a threat for heavy snow/ice on the northern periphery
of the expanding precipitation shield this period from the central
Plains through the Great Lakes and interior Northeast and southern
Canada. Expect lake-effect snows into the weekend given lingering
cold/windy flow.

Upstream, there is a growing guidance signal for the amplification
of the overall flow significantly into later week across the
nation and adjoining oceans, but with limited precipitation
re-emergence overall at this point. Organized rains stay mainly
off the West Coast this period, with significant eastern Pacific
storm development held just offshore. Renewed shortwave approach
out from the West and potentially the northern stream will
meanwhile help carve out an amplified central to east-central
upper trough position later week into next weekend, but responding
surface system development does not seem to have deep moisture
inflow in the wake of the aforementioned lead main system, so
expect an expanding area of overall moderate rainfall signature
with a main focus likely to lift from the Southeast to up the East
Coast next weekend with modest coastal low genesis and Atlantic
inflow that could offer a late period interior snow threat over
the Northeast to monitor.

Kong/Schichtel


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, experimental excessive rainfall
outlook, 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/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml

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