Heavy Snow in Oregon, February 14, 2019

Area Forecast Discussion
National Weather Service Pendleton OR
758 PM PST Wed Feb 13 2019

.UPDATE...The flow aloft will become southerly again which will
push moisture northward ahead of the next weather system that will
move in off the Pacific. Cold air in place over the CWA
(especially the northern CWA) will cause the precipitation to
start out as all snow by Thursday morning. During the day the
cold air will be overrun by warmer above freezing air from the
south and erode the cold air at the surface along the Blue
Mountain Foothills eastward and southward. In these areas snow
levels will rise to above 5000 feet and change all snow or mixed
precipitation to rain by Thursday evening. In the Lower Columbia
Basin there is the potential for a significant icing event with
freezing rain as the warmer air overruns the trapped cold surface
air. Farther north and west this will be mainly a snow event with
Winter Storm Warnings from North Central Oregon northward to the
Yakima and Kittitas Valleys. The WA Cascade east slopes and the
Lower Columbia Basin/Blue Mountain Foothills are under a Winter
Weather Advisory for the snow and then mixed precipitation (except
all snow over the WA Cascades, but just not enough for a warning).
As mentioned above the mixed precipitation along the Foothills of
the Blues and the Blues will change to all rain later Thursday.
Showery weather will then persist over the region as an upper
trough over the Pacific moves into the northwest and deepen with
colder air pushing down from Canada again by Sunday. This will
bring about another period of cold weather, but mostly dry
conditions, except for some mountain snow showers. 88

&&

.AVIATION...06Z TAFs...Improvement will continue this evening, but
then deteriorate again by morning as the next winter storm moves
into the region in the morning. Expect times of MVFR and/or IFR
conditions at most TAF sites due to lower CIGs or VIS in snow or
mixed precipitation. Winds will become southerly again for the
Oregon TAF sites and will remain northerly in the low levels over
the WA TAF sites, but will not be too strong...5 to 15 Kts at
most. 88

&&

.PREV DISCUSSION... /issued 234 PM PST Wed Feb 13 2019/

SHORT TERM...Tonight through Friday night...The upper level trough
stretching from central canada back to the eastern Pacific has now
split. The northern portion continues moving east into the northern
Plains while the southern portion has formed a closed low off the
California coast. A cold front stretches between the two features
which is slowly being torn apart and weakening but still producing
some light precipitation. This front will slowly sag southward this
evening then stall over central Oregon before beginning to lift
northward late tonight and Thursday. This occurs because the low off
the California coast will begins to lift towards the Pacific
Northwest in response to a colder upper level low pressure system in
the Gulf of Alaska is dropping southward. This will eject the
California low and its moisture across the forecast area on
Thursday. This will bring warmer air aloft over the central and
eastern portion of the forecast area while a pool of deeper cold air
remains trapped over north central Oregon and the east slopes of the
Washington Cascades. The result will heavy snow occurring in the
region under the cold pool, mixed precipitation across the Lower
Columbia Basin and Blue Mountain Foothills and then rain over the
eastern Oregon mountains with snow levels around 5000 to 6000 feet.
Winter storm warnings and winter weather advisories have been issued
for the impacts expected due to the heavy snow and mixed
precipitation through Thursday evening.

The colder Gulf of Alaska low pressure will approach the Oregon
coast on Friday. The warm front associated with the low will advance
northward through northern Oregon into southern Washington and
temperatures will rise. There will be some light precipitation,
generally in the form of rain at the lower elevations and snow at
the higher elevations through Friday. Latest guidance has increased
snow levels from the previous. As the low moves northeastward Friday
night and a cold front moves toward the area, temperatures will
begin to fall into Saturday.

LONG TERM...Saturday through next Wednesday...The active pattern
continues this weekend into next week with general long-wave
troughing continues as multiple upper-level lows and shortwave
trough drop south along the east side of blocking high into the
PacNW. Expect cold temps and snow showers over the weekend as a
series of lows and trough rotate through the PacNW, with the best
chances mainly along the higher terrain. Could be a brief respite on
Monday as transient ridging tries to bring drier and slightly warmer
weather, but this will be short-lived. Next Tuesday into Wednesday,
as the blocking ridge amplifies north into Alaska, the polar jet
will dive south and allow for more disturbances to work into the
PacNW bringing more snow and bring a reinforcing shot of cold air.
With the persistent troughing and north to northwest flow aloft,
temps will remain quite cold for this time of year, running 5-15
degrees below normal with highs generally in the mid 20s to 30s and
lows in the teens to lower 20s.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  24  29  29  41 /  20 100  40  30
ALW  26  30  30  39 /  20 100  50  40
PSC  22  31  27  37 /  10 100  50  10
YKM  19  30  27  35 /  10 100  80  20
HRI  24  30  26  38 /  10 100  40  10
ELN  15  30  24  35 /  10 100  80  20
RDM  28  40  27  41 /  40  90  40  30
LGD  29  41  33  37 /  30  90  50  40
GCD  34  45  31  38 /  50 100  40  40
DLS  29  32  32  38 /  20 100  70  30

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 1 AM to 10 PM PST Thursday for ORZ510.

     Winter Weather Advisory from 4 AM to 10 PM PST Thursday for
     ORZ044-507-508.

     Winter Storm Warning from 4 AM to 10 PM PST Thursday for ORZ041.

WA...Winter Weather Advisory from 4 AM to 10 PM PST Thursday for
     WAZ028-029-520.

     Winter Storm Warning from 4 AM to 10 PM PST Thursday for WAZ024-
     026-027-521.

&&

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