Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 222127

Area Forecast Discussion
National Weather Service Pendleton OR
226 PM PDT Mon May 22 2017

.SHORT TERM...Tonight through Thursday...High pressure over the
region will continue into Tuesday but begin to flatten as a low
pressure system moves into western Canada. A cold front will then
move across the region Tuesday night bringing cooler and windy
conditions that will persist into Wednesday. Precipitation threat
from this system looks minimal as the main moisture stays well to
the north. A cool northerly flow will continue behind the front on
Thursday but with a small shortwave expected to drop southward over
the region. This should generate enough instability to lead to some
showers and possible thunderstorms over portions of the forecast

.LONG TERM...Thursday Night through Monday...The extended
period will start off with a departing shortwave trough moving
across eastern OR and into SW ID Thursday night and Friday morning.
Wrap around moisture associated with this mid/upper level low will
keep conditions mostly cloudy with a chance of rain showers...mainly
from the Blue Mountains south and east. The remainder of the
forecast area should dry out, under partly cloudy skies Thursday
night/Friday morning. Later in the day on Friday the forecast area
will be under a northerly flow pattern behind the departing low.
There could be just enough lingering moisture and instability for a
few thunderstorms to develop over the eastern mountains Friday
afternoon and evening. Much of the rest of the CWA is now looking
dry for Friday afternoon. Temperatures begin a warming trend on
Friday...reaching the 70s to lower 80s for afternoon highs...except
60s in the mountains. For the upcoming holiday weekend, the latest
model guidance has shifted the aforementioned trough out of the area
to the east faster than previous runs...with a building upper ridge
replacing it. For Saturday and Sunday, the 12z GFS, ECMWF and their
respective ensemble means are now in excellent agreement that the
CWA will see building heights and above normal temperatures. On
Sunday, the 12z GEFS and EPS means showed a 580dm ridge centered on
our area with 2m temperature anomalies between +3 to +6C. 850mb
temperatures are forecast to push 20C by Sunday and next Monday over
the lower basin and foothills. This would translate to high
temperatures between 85 to 95 degrees in the lower elevations. The
official forecast high temperatures were nudged several degrees in
this direction. With the warmer, somewhat moist air-mass progged to
move into the area over the weekend the latest guidance is
indicating increasing atmospheric instability parameters. This is
especially true heading into Sunday and next Monday, as the CWA will
be under a southerly return flow once the ridge shifts east. The
models are also indicating the potential for a few weak waves to
move over the top of the ridge toward Sunday and Monday. All of
these factors will lead to a slight chance of thunderstorms in the
mountains later Sunday and especially next Monday afternoon/evening.
There is plenty of time to watch this thunderstorm potential and the
timing and locations of any thunderstorms is likely to shift as the
models resolve this weather pattern. 77


.AVIATION...00z TAFs...VFR conditions with mostly clear skies and
winds less than 10 kts expected through at least midday Tuesday. A
band of sct to bkn cirrus near 25-30k ft agl is currently moving
through the center of the forecast area. There are also a few pop up
cumulus clouds over the Blue Mtns, which will dissipate around
sunset. Overnight and on Tuesday, expect just a few cirrus clouds
again...otherwise clear skies. Westerly winds will begin to increase
Tuesday afternoon as a marine push and associated cold front
approach the area. Westerly winds between 10 to 20 kts are expected
after 23/21-24z. KDLS will see these westerly winds first, and will
have the highest speeds...with gusts up to 30 kts possible late. 77


PDT  56  88  52  67 /   0   0   0   0
ALW  60  90  55  69 /   0   0   0   0
PSC  55  94  55  74 /   0   0   0   0
YKM  57  92  52  73 /   0   0   0   0
HRI  55  91  55  72 /   0   0   0   0
ELN  55  87  50  65 /   0   0   0   0
RDM  48  89  44  70 /   0   0   0   0
LGD  50  84  49  65 /   0   0   0  10
GCD  51  88  48  68 /   0   0   0   0
DLS  59  90  55  71 /   0   0   0   0




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