Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1051 AM EST Mon Feb 11 2019

Valid 12Z Thu Feb 14 2019 - 12Z Mon Feb 18 2019

...Overview...

Models/ensembles show strong consensus that a Rex block pattern
across the central/north Pacific, extending from near Hawaii to
Alaska, should persist through the next week, leaving the flow
regime across the CONUS largely quasi-zonal. Teleconnections
relative to the strongest 500 hPa positive height anomaly center
continue to favor a positively-tilted mean trough near the Pacific
Northwest with weak positive height anomalies from the southern
Plains lumbering eastward into the Southeast and a broad region of
modestly cyclonic upper-level flow across much of the CONUS.
Shortwave energy ejecting from the northeastern Pacific every
couple days will move into then cross the CONUS, undergoing
gradual amplification in the broad cyclonic flow. Additionally, a
persistent and relatively strong thermal gradient from the central
U.S. to the Ohio Valley/Great Lakes will serve to intensify
another low pressure system by later this week as it tracks into
the interior Northeast.


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

From the end of the short range (Wednesday) into the medium range
(Thursday) the 00Z/06Z models/ensembles showed a large amount of
spread in the northeastern Pacific regarding the evolution of a
very sharp/sheared trough that will either come into WA/OR in one
stronger piece via the northern portion (ECMWF/Canadian) or two
weaker pieces (GFS/UKMET). Continuity and majority of ensembles
favored the ECMWF-led consensus and opted to use that cluster as
the basis for the forecast. This preference carried through the
entire medium range period due to the timing differences
downstream (GFS quicker, ECMWF slower). By Fri/Sat this resulted
in a storm track out of the mid-MS Valley and into the Northeast
but at a pace about 18-24 hrs slower than the 00-06Z GFS runs.

In the wake of the late week eastern low pressure system, models
have at least come into better agreement on the nature of the flow
across the western/central U.S. by the weekend. There, the GFS was
more agreeable with the ECMWF as numerous areas of Pacific
shortwave energy push inland. A more significant trough should
push into the western U.S. by Sun-Mon as shown by the majority of
deterministic solutions and ensemble means. Both the GEFS mean and
ECMWF ensemble mean were similar on timing/amplitude though the
deterministic runs highlighted the remaining differences in
details. This will carry a southern stream system through the
Southwest with high pressure nosing southeastward out of southern
Canada through the High Plains into the Midwest.


...Weather Highlights/Hazards...

The persistent upper trough along the West coast will produce
multiple rounds of low-elevation rain and mountain snow (with
varying snow levels) from California to the Pacific Northwest.
Systems will also spread rain/snow east into the interior western
U.S., with heavy snow possible at the higher elevations. The low
pressure system moving from the central U.S. toward the Great
Lakes Thu-Fri will likely produce an area of wintry weather
along/north of the surface low track. The extent of winter weather
and the degree to which heavy snow may be possible remains
somewhat uncertain given the model differences described above.
The same holds true for winter weather potential in the Northeast
Fri-Sat. While at least some wintry weather is likely in warm
advection ahead of the warm front, any potential coastal low
development would enhance the potential for heavier precipitation
across New England, with the best chances for significant snows
across the interior. Farther south, the cold front will likely
produce widespread rains from the lower Mississippi Valley to the
Eastern Seaboard.

Well below average temperatures are expected to persist from the
interior Pacific northwest to the northern Plains through the
forecast period. Max/min temperatures ranging from 10 to 30 deg F
below average will be possible through the week and into the
weekend across these areas. Temperatures will initially be above
average over the southern/central Plains (Thu) to the Eastern
Seaboard (Thu/Fri), but then colder temperatures should spread
farther south/east in the wake of the low pressure system, with
temperatures 5 to 15 deg F below average across much of the
central/eastern states. The exception will be areas from the
southern Plains to the Southeast where temperatures will remain
near seasonal norms even into the weekend.


Fracasso/Ryan


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