Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 130310

Area Forecast Discussion
National Weather Service Pendleton OR
710 PM PST Mon Nov 12 2018

.UPDATE...An upper level ridge is moving over eastern WA and OR
tonight. A cold pool has formed under strong surface inversions
in the Lower Columbia Basin. Fog and stratus has formed in the
stagnant air trapped under the inversions. Mostly clear skies
cover the area above the cold pool. The sun angle is too low this
time of year to provide enough daytime heating to break the
inversions in the afternoon so expect the cold pool to persist
until a front brings enough wind to disturb the cold pool. Due to
the cold pool I lowered high temperatures in the Columbia Basin
tomorrow to make the highs similar to today. I also increased sky
cover in stratus and fog covered areas. The rest of the area will
have cold nights with wide diurnal swings to warm afternoons.


.PREV DISCUSSION... /issued 240 PM PST Mon Nov 12 2018/

SHORT TERM...Tonight through Thursday. A ridge of high pressure
dominated the areas weather with dry conditions and created an
inversion that produced fog in and near the Columbia Basin. The
patchy freezing fog had expanded into the foothills of the blue
mountains...ykm and kittitas valleys and is forecast to move into
north central Oregon even more tonight. This pattern will persist
into Tuesday and the afternoon temperatures will struggle to
climb out of the 30s in the fog. Elsewhere high temps are forecast
in the 40s and 50s. A weather system will move into the pacnw
Wednesday and spread showers to the wa/or cascades and blue
mountains. In addition sfc winds increase and the fog is expected
to decrease by Wednesday afternoon and high temps should rebound
into Thursday. As the system moves away from the area...drier
conditions can be expected but showers will linger along the
Washington Cascades.

LONG TERM...Thursday night through Monday...Good model consensus
for the long term with ensemble support. Amplifying ridge
approaching the West Coast with a short-wave trough with surface
cold front sliding south across the PacNW down the front side of the
ridge and may bring a few mountain showers Thu night and Friday.
Enough mixing with the system passage may help to scourge out the
fog/stratus in the Columbia Basin, but do keep some overnight and
morning patchy fog for valleys and basins. For the weekend the
overall pattern is looking like the strong ridge settling over the
PacNW that will block and split the storm track with the polar jet
well off to our north and a cut-off low diving south into
California. With increasing subsidence and strengthening low level
inversion under the ridge and reduced mixing and light winds, expect
fog/stratus to develop and expand in coverage over the weekend into
early next week. The time of the year where the sun angle is not
strong enough to burn off the fog/stratus in the daytime. Have
trended high temps down in the Columbia Basin for the end of the
long term to reflect this. May need to be further adjusted down if
confidence increases. Mountains will see above normal temps above
the stratus and inversions with colder temps in the Columbia Basin

AVIATION...00Z TAFs...Fog and/or low stratus has enveloped nearly
all of the Lower Columbia Basin and Gorge with LIFR to MVFR
conditions. Expect lowering CIGs and Vis tonight. Fog/stratus could
be particularly thick near the foothills of the Blues with brief
VLIFR conditions possible. Conditions could improve slightly
tomorrow. Outside of the fog/stratus just a few high clouds
expected. Light winds will continue through tomorrow.


PDT  24  30  27  44 /   0   0   0  10
ALW  26  32  32  45 /   0   0   0  20
PSC  26  36  31  42 /   0   0  10  10
YKM  23  36  28  43 /   0   0  20  20
HRI  25  37  29  44 /   0   0   0  10
ELN  23  40  27  42 /   0   0  20  30
RDM  12  48  26  56 /   0   0   0  20
LGD  24  46  30  50 /   0   0   0  10
GCD  25  51  28  54 /   0   0   0  10
DLS  29  37  36  43 /   0   0  20  30


WA...Air Stagnation Advisory until 11 AM PST Tuesday for WAZ027.



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