Winter Storm Warning 3, NWS Pendleton, OR

Area Forecast Discussion
National Weather Service Pendleton OR
1152 PM PST Fri Feb 7 2020

.UPDATE...A cold front will push through the region overnight.
Pressure gradients tighten producing windy conditions. Upper level
winds show 50kts plus that could mix to the surface at times
overnight and into tomorrow. This had prompted a wind advisory
for portions of the region that includes the gorge and north
central Oregon and eastward into the basin and blue mountain
foothills overnight and into tomorrow.

&&

.PREV DISCUSSION... /issued 824 PM PST Fri Feb 7 2020/

UPDATE...Upper ridge is weakening and a cold front is now working
its way eastward and is crossing the Washington Cascade east
slopes at this time. Snow has begun to fall at KSMP so far, but
there has not been any precipitation reported east of KSMP. The
cold front will bring a burst of snow to the eastern mountains and
the Cascade east slopes late tonight and Saturday morning...with
rain showers in the lower elevations. There is a winter weather
advisory for the WA Cascade east slopes until 10 PM Saturday and
on for the northern Blue Mountains in effect from 10 PM this
evening until 10 PM Saturday. Once the cold front moves through
the region the flow becomes northwest again which is upslope into
the Blue Mountains. This could prolong upslope snow showers into
the Blues into Sunday, and therefore may need to extend the WSW
for the northern Blues beyond 10 PM Saturday. Otherwise a dry
northerly flow with cool conditions develops for at least the
first half of next week with seasonal temperatures. 88

AVIATION...06Z TAFs...VFR conditions are expected to prevail
through the next 24 hours, but there could be MVFR and possibly
even IFR conditions in rain/snow showers at all TAF sites by
Saturday morning, continuing into the afternoon before the showers
end by evening. It will also be breezy to windy with the cold
front and immediately after the front passes with wind speeds of
15 to 25 kts and gusts up to 35 kts possible through Saturday
morning. 88

PREV DISCUSSION... /issued 128 PM PST Fri Feb 7 2020/

SHORT TERM...Tonight through Monday...Pattern change is taking
place tonight. The persistent northwest flow is turning westerly as
a weather system in the Gulf of Alaska prepares to move into the
Pacific Northwest. This system will push a cold front into western
Washington and Oregon this evening and then over the Cascades around
midnight and then trough the forecast area late tonight through
Saturday morning. This system will bring with it cooler air and
lowering snow levels behind the cold front. Snow levels will drop to
around 2000 feet behind the front. This will lead to accumulating
snow in the eastern mountains and along the crest of the Cascades.
The northern Blue mountains will see 6 to 14 inches of new snow by
Saturday night so a winter weather advisory has been issued. There
will also be some windy conditions ahead of and behind the frontal
passage with some blowing snow possible in the mountains. The
weather system will drop into the western Great Basin Sunday leaving
the forecast area under a dry cool northerly flow through monday.

LONG TERM...Monday night through Friday...Quieter weather to start
the work week with cool, drier north to northwest flow on through
Monday as eastern Pacific ridge tries to nudge onshore. Earlier
model runs were showing a more significant trough/front dropping
south through the area on Tuesday/Wednesday, but recent runs have
been keeping ridge a bit further east, with a weaker trough clipping
the region and bringing a few mountain snow showers. Models are now
trending towards a stronger upper low/trough dropping south out of
BC over the PacNW Thursday into Friday. This would likely bring a
good round of mountain/valley snow with a chance of Basin rain.
Cooler, more seasonable temps next week with highs in the upper 30s
to lower 50s. Some locally gusty winds possible Tuesday with the
weak trough/frontal passage, but breezy to windy conditions possible
Thursday with the stronger trough.

HYDROLOGY...Excessive rainfall combined with snowmelt has cause
widespread flooding of creeks, streams and rivers across portions
of the forecast area. Rainfall has just about ended and some
locations are seeing water levels starting to recede, but flooding
continues as the water moves through the river systems. Some
rivers are expected to remain above flood stage through the
weekend. Colder temperatures are expected Saturday following a
cold frontal passage. A drier and cool northerly flow is expected
Sunday and through the first of next week allowing rivers to
continue to recede.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  44  29  45 /  60  30  30   0
ALW  43  45  30  46 /  80  60  30   0
PSC  44  51  29  49 /  20  10  10   0
YKM  38  51  26  49 /  30  10   0   0
HRI  43  48  29  48 /  30  20  20   0
ELN  35  44  26  46 /  50  20   0   0
RDM  36  43  26  44 /  30  20  10   0
LGD  37  38  29  40 /  90  80  40   0
GCD  36  37  28  41 /  50  70  40   0
DLS  43  46  32  50 /  50  30  10   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 4 PM PST Saturday for ORZ041-044-507-508-510.

     Winter Weather Advisory until 10 PM PST Saturday for ORZ502.

WA...Wind Advisory until 4 PM PST Saturday for WAZ024-028-029-521.

     Winter Weather Advisory until 10 PM PST Saturday for WAZ030.

     Winter Weather Advisory until 10 AM PST Saturday for WAZ520.

&&

97/