Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 230631 AAB

Area Forecast Discussion
National Weather Service Pendleton OR
1020 PM PST Sun Jan 22 2017

updated the aviation discussion

.UPDATE...An area of pcpn over our eastern area that produced an
inch or two of snow in the blue mountains was slowly moving away
from the region. Meanwhile patchy/freezing fog had developed over
portions of the lower columbia basin especially along interstate 82
between yakima washington and richland already and have added this
to the forecast. The fog is expected to increase in coverage
overnight that includes the remaining portions of the columbia basin
in washington/oregon and the forecast was updated. Elsewhere some
showers are expected to move into central oregon later tonight as a
low pressure system approaches the two state area and the present
short term forecast appears on track.


.AVIATION...areas of mvfr and lcl ifr conditions are expected at all
taf sites into tomorrow. Taf sites kykm and kpsc could experience
areas of ifr conditions in fzfg after 08z before conditions slowly
improve after 16z. Elsewhere snow showers are expected to effect taf
sites krdm and kbdn after 12z and then pcpn should lessen after 20z
with improving conditions expected.


PREV DISCUSSION... /issued 229 PM PST Sun Jan 22 2017/

SHORT TERM...Tonight through Tuesday night...A weather system
continues to move across the Pacific Northwest this afternoon. There
is a large area of precipitation associated with a warm front moving
up across the Lower Columbia Basin and the northeast mountains and
Washington Cascades...followed by a cold front. A southeast upslope
wind is enhancing precipitation over the Yakima and Kittitas Valleys
and the Cascade east slopes where several inches of snow has fallen.
At the same time downslope southeast winds off the Blue Mountains
has resulted in very little precipitation if any over the Blue
Mountain Foothills and the southern most areas of the Lower Columbia
Basin. There has been some light freezing rain in the Lower Columbia
Basin...mostly north of the Horse Heaven Hills...but warming
temperatures has been changing the freezing rain to rain with less
than a tenth of an inch of ice accumulation. Snow amounts in the
mountains and in the Yakima/Kittitas Valley areas are not enough to
warrant any advisories. This system will depart the region tonight
but then another weather disturbance will move across the southern
portions of the CWA on Monday as an upper low pressure system moves
southward along the coast. This will be followed by a northerly flow
by Tuesday with the flow becoming northerly. There will be some
moisture in what appears to be a back door cold front but at this
time it looks to be minor any may only produce light snow showers in
the mountains or flurries in the lower elevations. It will turn
colder beginning Tuesday in the northerly flow. Also with the
amplified upper ridge over the west valley inversions will develop
again resulting in low clouds and patchy fog/freezing fog and
possibly air stagnation issues. 88

LONG TERM...Wednesday through Sunday...An upper level ridge will be
over the forecast area for much of the extended period.  There will
be a slight chance of snow showers...mainly in the Mtns for
Wednesday into Thursday as weak disturbances ripple through the
upper level ridge. Any snow accumulations will be very light.
Otherwise expect patchy freezing fog in the Lower Columbia Basin and
adjoining valleys overnight and in the early morning hours. After
the weak weather system exits Thursday night expect a stronger upper
ridge to build over the area through at least Saturday night. This
will allow areas of fog/freezing fog to expand and linger through
much of the day for locations below about 2500 feet MSL. The low
level inversions will strengthen over the weekend and may lead to
air quality issues for the lower valleys/basins. A weak system will
ride over the top of the ridge next Sunday...this will bring a
chance of snow along the East Slopes of the WA Cascades. This system
will likely not be strong enough to mix out the lower elevation
fog/stratus. The remainder of the forecast area should remain dry.
Temperatures were adjusted to show this trend (smaller diurnal range
for areas affected with fog). Temperatures through each day of the
long term period are expected to be in the mid 20s to mid 30s for
highs and lows will be between 15 to 25...except some single digits
and lower teens in the mtns/high mtn valleys. 77


PDT  31  32  20  31 /  10  10  10  10
ALW  33  33  23  31 /  20  10  10  10
PSC  29  31  19  30 /  10  10  10  10
YKM  26  31  14  29 /  10  10   0   0
HRI  30  32  20  30 /  10  10   0  10
ELN  25  30  14  29 /  10  10   0  10
RDM  25  30  12  30 /  30  30  10  10
LGD  26  30  16  27 /  20  10  10  20
GCD  27  30  15  28 /  20  30  10  20
DLS  33  33  22  34 /  10  20   0  10




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