Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 181722 RRA

Area Forecast Discussion
National Weather Service Pendleton OR
1022 AM PDT Fri Aug 18 2017


.UPDATE...A flat westerly flow remains over the Pacific Northwest
this morning and water vapor imagery shows a weak cold front draped
across southern British Columbia and the Olympic Peninsula. This
front will cross the area later today with the main impact being
increased pressure gradients along the Cascades. This will bring 15
to 25 mph winds through the Columbia Gorge and Cascade gaps this
afternoon and evening before dying down overnight. Elsewhere, winds
will be 5 to 15 mph. There may be some scattered higher clouds with
the front but have kept mostly clear skies for now. With higher 500
MB heights today, temperatures will be a few degrees warmer than
yesterday with highs in the upper 80s to lower 90s and mainly in the
80s in the mountains. Temperatures this morning were quite cool in
the mountains so have nudged temperatures tonight down closer to
what was seen this morning. Smoke from fires along the Central
Oregon Cascades was significant overnight as fires remained active.
Have expanded the coverage of areas of smoke southward to include La
Pine where the smoke is evident on webcams. Forecast update already
out. Perry

.AVIATION...18z TAFS...VFR conditions are forecast to continue
through the next 24 hours at all taf sites. Skies will remain mostly
clear but there will be some smoke concerns impacting KRDM and KBDN
due to local fires which could impact visibility and produce a smoke
layer. Westerly winds will increase to between 10-20 kts this
afternoon, especially at KDLS, KRDM, KBDN and KPDT. Winds will then
generally decrease back below 10 kts in the overnight hours.


.FIRE WEATHER...A dry westerly flow last night resulted in poor to
moderate humidity recoveries for many areas.  This also brought the
Haines to a moderate category of 5 last night which was problematic
for nearby fires.  It will be another day with afternoon humidities
ranging from 8-20 percent and a Haines of 5.  Another concern will
be the increasing winds this afternoon and evening.  A weak marine
surge will cause winds to increase through the Cascade gaps and the
Eastern Columbia River Gorge where winds will gust to 25-35 mph late
this afternoon.  Winds along the I-84 corridor from Arlington to
Pendleton and down along the Columbia Deschutes Plateau will
increase as well with gusts to 25 mph in some areas.  The duration
of winds and low humidity will be about 2-3 hours that will need to
be monitored closely. Because the weather pattern changes little
from now through the Solar Eclipse, no major changes are expected in
temperatures, humidity, and winds.  Wister


.PREV DISCUSSION... /issued 259 AM PDT Fri Aug 18 2017/

SHORT TERM...Today through Sunday night...A ridge of high pressure
will keep dry and stable conditions with warm temperatures over the
forecast area today. There will be a cold front moving in from the
north by this evening which will bring tightening pressure gradients
and a marine push of cooler air off the Pacific. However, the cool
down will only be slight and the main effects will be breezy to
windy conditions through the Cascade gaps and the Columbia River
Gorge this afternoon and evening. However the winds are neither
expected to reach advisory criteria nor is the combination of wind
and relative humidity expected to reach critical fire weather
levels. A northwest flow aloft will follow behind this cold front
for Saturday and Sunday and temperatures will be several degrees
cooler than today. Temperatures will not change much for the rest of
the short term forecast period with not much change in 850 mb
temperatures or heights. It looks to be dry and stable both Saturday
and Sunday. There will be some increase in clouds late Sunday as
another weak cold front approaches by Sunday night. These clouds
should move out to the east by Monday morning. 88

LONG TERM...Monday through Friday...A weak shortwave trough will be
exiting the forecast area by midday Monday. There could be some
scattered mid/high level clouds around Monday morning, especially
over our southern Washington zones...with clear skies expected
further south over much of eastern Oregon. Depending on how current
wildfires progress, there could also be some patchy smoke in parts
of Central Oregon on Monday. Temperatures will start off in the
upper 40s to 50s most areas Monday morning, before rising into the
80s to lower 90s in the afternoon...winds will be light, less than
10 mph. By Tuesday, the flow turns more southerly in association
with another very weak disturbance. Model guidance indicates some
marginal instability, mainly over Central Oregon and the southern
Ochoco-John Day highlands. Latest guidance seems to be keeping most
of the potential t`storm activity further south Tuesday
aftn/eve...but for now followed the previous forecast to indicate a
slight chance of t`storms over the above mentioned areas. The
remainder of the forecast area remains dry on Tuesday, with very
warm temperatures. Highs will reach the lower to mid-90s in the
valleys/basins, with 80s in the mountains. Heights begin to fall on
Wednesday as the next, more amplified trough approaches the Pacific
Northwest. Models are indicating higher levels of moisture and
instability over the eastern half of the CWA on Wednesday. As this
system moves through, expect a chance of showers, with a slight
chance of t`storms, again mainly over the eastern half of the CWA. A
few showers and perhaps a t`storms or two could linger into Thursday
as the main trough axis and associated frontal boundary move
through. Westerly winds are also likely to increase (becoming
breezy) as cold air advection develops, along with tightening
pressure gradients. Temperatures will be 5-10 degrees cooler on
Thursday. For next Friday, the latest guidance is in fairly good
agreement that the aforementioned trough will swing quickly
eastward...leaving our forecast area under basically a zonal,
westerly flow. This should mean dry, but continued cooler weather.
Highs will only reach the lower to mid-80s...except 70s mountains.
Overnight lows could dip into the 40s and lower 50s areawide. 77


PDT  89  57  86  60 /   0   0   0   0
ALW  92  62  87  63 /   0   0   0   0
PSC  93  58  89  57 /   0   0   0   0
YKM  92  55  88  59 /   0   0   0   0
HRI  92  58  89  59 /   0   0   0   0
ELN  87  59  83  59 /   0   0   0   0
RDM  91  47  84  49 /   0   0   0   0
LGD  90  51  83  54 /   0   0   0   0
GCD  90  50  85  51 /   0   0   0   0
DLS  89  60  87  62 /   0   0   0   0




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