Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1103 AM EST Thu Feb 07 2019

Valid 12Z Sun Feb 10 2019 - 12Z Thu Feb 14 2019

...Overview and Guidance/Predictability Assessment and
Preferences...

Pacific flow remains fraught with uncertainty surrounding a
stubborn upper high near the Gulf of Alaska. Troughing will
generally stay focused near/along the west coast of the lower 48,
reinforced either from the north (on the east side of the upper
ridge) or from the west (underneath the upper ridge). An upper
high over the Florida Straits will weaken and split E-W from
Mexico to the Great Antilles, opening up broad troughing into the
east. However, how this unfolds is quite uncertain as evidenced by
the notable timing/track differences among the guidance from as
early as 48 hrs near Alaska.

By day 4 (Mon), the 00Z ECMWF and its ensemble mean, along with
the UKMET and to some extent the CMC, split the troughing across
the western U.S. into two distinct areas as upstream energy coming
in kicks the first trough farther east. The 00Z and 06Z GFS and
GEFS, on the other hand, had a singular trough that hangs farther
west as the upstream energy joins with the preexisting trough. The
former seems more likely, and since the model consensus leans that
way, the medium range products mainly incorporated those solutions
through day 5. By days 6-7, the GFS and GEFS became useful again
as, after a different evolution to get there, the two main systems
of the upper low over the Great Lakes and the upper low offshore
of the western U.S. look fairly similar at day 6. Additionally,
the general troughing the 00Z GEFS members have in the
southwestern U.S. at day 7 fit better with what teleconnections
(based on the persistent upper ridge in the Gulf of Alaska) would
suggest.

At the surface, there is better agreement today that a surface low
and associated fronts will develop in the lee of the Rockies, move
across the Mississippi Valley on Monday night and Tuesday, and
into the Upper Midwest Tuesday night and Wednesday. However,
details in timing, placement, and strength of the low will have to
be ironed out later. A couple more systems will sink through the
West as well.


...Weather Highlights/Hazards...

Late this weekend and into early next week another round of
potentially heavy precipitation will spread into the Lower to
Mid-Mississippi and Tennessee Valleys as moisture surges northward
atop a warm front along the Gulf Coast. As the low pressure system
strengthens into the Midwest on Tuesday, precipitation is expected
to push through the Ohio Valley and into the
Mid-Atlantic/Northeast. With temperatures near/below freezing,
wintry precipitation will be possible on the northwest/north side
of the low and well ahead of the warm front. In the West where
persistent troughing will remain, moderate precipitation (valley
rain and mountain snow) is expected across the Pacific Northwest
at days 4-5, shifting southward on day 6-7 to take aim at mainly
California.

Much below average temperatures will remain anchored over the High
Plains throughout the medium range period (MT/ND/SD). The rest of
the West is forecast to see below average temperatures due to the
persistent troughing and episodic cooler surges of Canadian air.
This may result in some record cold temperatures for coastal WA/OR
and northern California Sun/Mon. Slightly below average
temperatures will bleed into the Upper Midwest and then Great
Lakes behind the midweek system. A surge of above average
temperatures will precede the cold front especially Tuesday.


Tate/Fracasso


WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation and winter weather outlook
probabilities are found 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