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000
FXUS02 KWBC 170647
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
147 AM EST Mon Feb 17 2020

Valid 12Z Thu Feb 20 2020 - 12Z Mon Feb 24 2020

...Guidance/Predictability Assessment...

Recent model and ensemble forecast spread remains below normal for
the rest of this week, increasing early next week. However,
lingering system timing and emphasis differences seem well
mitigated by the blending of overall reasonably well clustered
guidance through medium range time scales. The WPC medium range
product suite was based primarily from a composite blend of the 18
UTC GFS/GEFS mean, 12 UTC ECMWF/UKMET/Canadian/ECMWF ensemble mean
and the National Blend of Models. Opted to marginally trend WPC
blend weighting from the models toward the ensemble means into
days 6/7 consistent with growing solution variance within the full
envelope of solutions. This strategy maintained good WPC
continuity. The latest 00 UTC GFS/GEFS/ECMWF/UKMET generally seem
in line with this WPC forecast.

...Weather Pattern and Hazard Highlights...

Cold post-frontal high pressure will settle over much of the lower
48. A positive tilt northern stream mid-upper level trough and
limited/spotty snow will progress from the Midwest to off the East
Coast Thu/Fri in response to deamplification of upstream ridging
aloft over west-central Canada. More organized precipitation
lingering from the southern Rockies to the South/Southeast U.S.
within a trailing and wavy cold frontal zone will gradually be
suppressed across the region.

Meanwhile, an amplified upper trough/low will develop in emerging
and separating southern stream flow off the West Coast.
Dynamics/height falls with inland trough progression and
cyclogensis/frontogenesis should support moderately increasing
precipitation to spread this weekend from the Southwest to the
south-central U.S. Activity may increase over the mid-lower MS/TN
Valleys through the South/southern Appalachians into Mon as fueled
by increasingly favorable Gulf of Mexico return moisture into a
region with ongong runoff issues. There is also some potential for
snow/ice on the cooled northern periphery of the precipitation
shield.

Upstream, development and weekend approach of an amplified upper
level trough and surface front may support potential for
increasingly wet flow into the Pacific Northwest Sun. Unsettling
sharp system digging over the West Mon would deliver cold air and
a terrain focusing snow risk down through the Great Basin/Rockies.


Schichtel

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

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

$$