Winter Storm Warning 15, NWS Pendleton, OR

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
941 AM PST Thu Dec 28 2017

Updated aviation discussion

.SHORT TERM...Today through Friday...Area of interest will be
mainly Washington where moisture flow is more focused and air mass
will remain subfreezing for the longest period. Impacts will be
greatest here due to the duration and potential depth of
precipitation mix. Winter weather advisories for a mixture of
freezing rain and snow will remain in effect for the counties in
Oregon bordering the Columbia River extending north into
Washington. The Oregon counties should be out of the cold air
during the evening and the advisory should be able to be lifted.
Models continue to try to warm atmosphere too quickly and will
keep the advisories going in Washington through tonight and into
Friday. If if looks like heavier precipitation is going to hit
these Washington areas, the winter weather advisory will need to
be upgraded to a warning. Will monitor closely for this.

&&

.AVIATION...18Z TAFS. KBDN and KRDM will see VFR conditions through
the forecast period. Snow or mixed precipitation will spread across
the area this afternoon and continue through the night. A transition
from snow to freezing rain to rain will occur at KPDT...KDLS...and
KALW this evening. Snow will begin to mix with and change to
freezing rain or rain at KPSC and KYKM later tonight.  MVFR
conditions will prevail...except KYKM, KPSC, and KALW will see
IFR/LIFR at times. Winds will generally be 10 kts or less through
the period...except KRDM and KBDN 10-15 kts tonight. Earle

&&

.PREV DISCUSSION... /issued 339 AM PST Thu Dec 28 2017/

LONG TERM...Friday night through Wednesday...An upper level
shortwave will drive a cold front across the region Friday night.
What's left of the shallow cold air mass in the Columbia Basin
should be gone by then. Decreasing showers across the lower
elevations are expected but with a continuation of rain/snow in the
mountains. A few mostly snow showers will continue in the favored
upslope areas on Saturday but an overall drying trend will take
place by Saturday night. A transitory ridge will build over the
region on Sunday into Monday with fair and cold weather. There could
be a little patchy valley fog. Highs will be in the 30s with some
20s mountains. On Tuesday have kept the forecast dry for now per the
ECMWF model. However the GFS is hinting at a weak system with a warm
layer aloft that could result in some light freezing precipitation.
Wednesday looks to be dry again with cold high temperatures mostly
in the 30s.  78

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  36  35  49  36 /  70  70  80  80
ALW  37  35  48  37 /  70  70  90  90
PSC  33  30  42  34 /  60  60  80  70
YKM  33  29  41  30 /  60  60  80  40
HRI  34  32  46  35 /  60  70  80  70
ELN  32  28  38  29 /  70  60  90  40
RDM  46  37  49  32 /  20  40  40  40
LGD  39  35  44  33 /  60  90  90  90
GCD  44  36  48  33 /  40  70  60  50
DLS  40  35  50  37 /  80  80  80  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 PM PST this evening for ORZ041-
     044.

     Winter Weather Advisory until 7 PM PST this evening for ORZ507-
     508-510.

WA...Winter Weather Advisory until 10 PM PST this evening for WAZ024-
     521.

     Winter Weather Advisory until noon PST Friday for WAZ026>028.

     Winter Weather Advisory until 7 PM PST this evening for WAZ029.

     Winter Weather Advisory until 10 AM PST Saturday for WAZ520.

&&

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