Area Forecast Discussion
Issued by NWS Pendleton, OR

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336
FXUS66 KPDT 241740 AAA
AFDPDT

Area Forecast Discussion...Update
National Weather Service Pendleton OR
940 AM PST Tue Jan 24 2017

Updated Aviation Discussion

.UPDATE...Widespread area of low clouds and fog cover the Columbia
Basin and surrounding areas. I issued a Freezing Fog Advisory for
the Foothills of the Blues and North Central Oregon until noon to
cover the low visibility and slick roads where the stratus deck
intersects with the surface between 1200 and 2500 ft MSL.
Northerly flow from the building offshore ridge may trigger a few
snow showers in upslope areas of the northeast OR mountains.
Coonfield

&&

.AVIATION...18Z TAFS...Fog and low stratus are keeping most
terminals IFR or even LIFR this morning. KPSC currently has lower
end MVFR CIGS and these should gradually lift...but likely stay MVFR
through the day. KRDM and KBDN are above the fog/clouds and should
remain VFR through at least the daytime hours. There is a chance for
some patchy fog/mist to affect KRDM overnight and into Wednesday
AM...with KBDN likely staying clear. For the terminals currently
experiencing fog/mist/low clouds expect gradual improvement through
the late morning and afternoon hours...very similar to yesterday`s
trend. Most terminals should be MVFR or better after 24/20-22z.
However, some lingering IFR CIGS will remain possible through the
afternoon at KPDT. Additional fog/mist/low clouds will likely
develop once again through the late evening and overnight hours.
This will continue into Wednesday morning. Terminals may again
experience at least tempo IFR/LIFR conditions during this time.
Winds will remain light...AOB 10 kts through the period. 77

&&

.PREV DISCUSSION... /issued 237 AM PST Tue Jan 24 2017/

SHORT TERM...A large upper level trough continues over the western
United States with most its storm energy south and east of the
Pacific Northwest. Meanwhile an upper level ridge is approaching the
West Coast which is beginning to place the Pacific Northwest under a
northerly flow. This northerly flow will persist through Wednesday
with a few snow showers over the far eastern mountains. A weather
system tries to move through the ridge late Wednesday and
Thursday but the ridge remains in place. Moisture associated with
this weakening system could spread few more widespread showers
over the forecast area during this time. Other concern will be the
fog and stratus that will remain trapped in the lower elevations
due to strengthened inversion under the ridge. Visibilities will
vary as the fog and stratus move and there could be some icy
conditions resulting from freezing fog and or freezing drizzle.

LONG TERM...Thursday night through Monday. A strong upper level
ridge will dominate the weather pattern across the region through
the weekend. Strengthening low level inversions will result in low
clouds and freezing fog for the Columbia basin and adjacent valleys.
Temperatures will remain in the mid 20s to mid 30s with light winds.
For the mid and higher elevations above the inversion skies will be
clear to partly cloudy. There will be more of a diurnal temperature
spread with highs in the 30s and lows in the teens. An upper level
short wave and front will move across the area Sunday night and
Monday. Not likely to see much precipitation with this system except
for some showers over the Cascades. However appears there will be
enough wind and cold advection aloft to mix out the low clouds and
fog in the Columbia basin and valleys. 94

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  35  26  33  27 /   0  10  10  20
ALW  35  29  34  28 /  10  10  10  20
PSC  35  30  34  27 /   0  10  10  10
YKM  34  22  33  26 /   0   0  10  10
HRI  35  27  34  27 /   0  10  10  20
ELN  32  21  31  24 /   0  10  10  10
RDM  34  19  34  19 /   0  10  10  20
LGD  31  20  30  22 /  10  10  10  20
GCD  30  18  30  20 /  10  10  10  20
DLS  39  30  39  30 /   0  10  10  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Freezing Fog Advisory until noon PST today for ORZ507-508-510.

WA...Freezing Fog Advisory until noon PST today for WAZ029.

&&

$$

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