Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 250948

Area Forecast Discussion
National Weather Service Pendleton OR
248 AM PDT Mon Sep 25 2017

.SHORT TERM...Today through Wednesday night...A weak weather
disturbance will move over the top of an upper ridge that is
building off the Pacific Northwest coast this morning. This will
bring mostly cloudy skies and a slight chance of some light rain to
the east slopes of the Cascades and the northeast mountains.
Precipitation amounts will be very light. The slight chance of rain
will persist into tonight and then will end Tuesday morning as the
upper ridge builds stronger and the ridge axis shifts eastward to be
closer to the forecast area. This will also result in decreasing
cloud cover. However the ridge axis will remain off the coast on
Tuesday resulting in a northerly flow over the CWA. While this will
be a dry and stable pattern it will also keep temperatures down from
reaching their full potential. The upper ridge will continue to
build into the region through the remainder of the short term period
with dry and stable conditions and a slow warming trend. High
temperatures today will be in the mid 60s to lower 70s in the lower
elevations...which will warm up to the mid 70s to around 80 in the
lower elevations by Wednesday. The warming trend will continue into
the extended period. Winds will be light through the short term
period and generally less than 15 mph. 88

.LONG TERM...Thursday through Monday...A large upper level ridge of
high pressure will be over the CWA for Thursday and Thursday night.
This will bring mostly clear skies, light winds and above normal
temperatures. The ridge axis shifts east by Friday, with a weak
trough/front moving in from the west late in the day. Skies start
off mostly sunny Friday morning, but then give way to increasing
clouds by afternoon. From late Friday afternoon into Friday night
there will also be a slight chance of rain showers over the
mountains...but any precip amounts are forecast to be very light.
There could be some lingering clouds and light showers on Saturday
morning...mainly in the eastern mountains. Otherwise, the trough
axis move east into Idaho by Saturday afternoon...with mostly sunny
skies and westerly winds of 8-15 mph in its wake. Temperatures will
remain mild Saturday afternoon, with highs reaching 75-80 in the
valleys/basins and mid-60s to lower 70s in the mountains. The latest
model guidance is in strong agreement that a flat upper level ridge
builds over the region Saturday night into Sunday...with a shot of
very dry mid-level air moving through during this time. A system
well to the north over the Gulf of Alaska could bring a weak warm
front through the forecast area on Sunday. This would allow for a
few more clouds...especially in Washington. There is a general
consensus from the latest model guidance that the aforementioned
flat ridge will be replaced by a broad upper level trough, which
will approach the Pacific Northwest coast sometime late next Monday
or Tuesday. The exact timing and details remain uncertain at this
time. However, did bring increasing clouds and a slight chance of
mainly mountain showers into the forecast toward the end of the
extended forecast period...especially day 8 (next Tuesday).
Temperatures look to remain generally above average through the
extended period...with daytime highs in the 70s to lower 80s and
overnight lows in the 40s to low 50s...except some 30s in the colder
mountain valleys. 77


.AVIATION...12Z TAFS...VFR conditions will prevail through the
period. There will some sct to bkn high level clouds moving through
the region today and into tonight. These will be mainly between 10K
to 25K FT AGL. Winds will remain generally under 10 kts through the
period...except at KDLS where westerly winds of 10-20 kts will be
possible this afternoon. 77


PDT  71  48  73  48 /   0  10   0   0
ALW  72  51  74  50 /  10  10   0   0
PSC  74  50  77  50 /   0  10   0   0
YKM  73  48  76  49 /  10  10   0   0
HRI  74  50  78  48 /   0  10   0   0
ELN  70  46  75  47 /  10  10   0   0
RDM  70  41  73  42 /   0  10   0   0
LGD  67  42  70  42 /  10  10  10   0
GCD  67  40  73  42 /  10  10  10   0
DLS  74  52  79  52 /   0  10   0   0





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