Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 202359 AAA

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
459 PM PDT Fri Apr 20 2018

Updated AVIATION discussion

.SHORT TERM...Tonight through Monday...Mostly sunny skies and
seasonably warm temperatures prevail this afternoon as a transient
ridge of high pressure is crossing eastern OR/WA. High clouds are
beginning to increase near the Cascade crest in advance of the next
system. Clouds will stream east across the local area this evening,
lowering and thickening overnight. By late tonight, initial precip
will spill over the crest, with the greatest coverage of precip
across the WA Cascade east slopes where chance PoPs will be used.
Further east, most areas will remain dry, with perhaps an upslope
isolated shower across the eastern OR mountains. Mild low
temperatures can be expected tonight with the increase in cloud
cover, with readings in the 40s for the lower elevations and mainly
30s in the mountains.

The mid/upper level trough and cold front will cross the area
Saturday morning, exiting to the east in the afternoon. Deep layer
moisture is quite limited and mainly to the north, so will confine
high PoPs to the immediate Cascade crest, with chance PoPs for the
east Cascade slopes, and slight chance PoPs for the eastern
mountains. Most lower elevation locations will remain dry. The main
concern with this system will be the wind. Tightening surface
pressure gradients and increasing mid level winds will yield breezy
to windy conditions for the Cascade gap locations. Winds will remain
below advisory criteria. Highs Saturday will be a few degrees cooler
than today, with readings mainly in the lower/mid 60s for the lower
elevations and upper 40s to lower 50s for the mountains.

Dry zonal flow will prevail Saturday night, with another weak short
wave progged to dig across the interior Pacific northwest Sunday.
With very little moisture to work with, dry conditions can be
expected. Cooler temperatures will work in behind the cold front,
with lows Saturday night in the 30s for the lower elevations, with
near freezing temperatures possible for the higher foothill
locations. Highs Sunday will be similar to Saturday. The trough will
exit to the east Sunday night, with ridging building back into the
region for Monday. Rather chilly temperatures will be possible
Sunday night, with the latest ECMWF depicting a freeze for the
lowest elevations. With the blend of models still in the mid/upper
30s and having better run to run continuity than the ECMWF
operational model, will stay closer to the blend. Temperatures will
begin a warming trend Monday with highs in the upper 60s to lower
70s for the lower elevations.

.LONG TERM...Monday night through Friday night...A strong mid-upper
level ridge of high pressure will persist over Pacific Northwest
through Thursday afternoon. During the day on Thursday, a large mid-
upper level trough will be near 132W off the northern California
coast and will begin transporting a moisture plume inland Thursday
night and thus introduce a slight chance of rain showers over higher
terrain in central Oregon. The trough then becomes negatively tilted
during the day on Friday and moves into SW Oregon by Friday
afternoon for a chance of rain showers in the higher mountains of
central Oregon Friday afternoon and a slight chance of showers
elsewhere lower terrain in central Oregon and in north central
Oregon as well as in the southern Blue Mountains in the afternoon.
Friday the negatively tilted, mid-upper level trough swings into the
forecast area thus bringing dynamic lift for a chance of showers
spreading northward into the lower Columbia Basin Friday evening.
Models show an unstable atmosphere in central Oregon on Friday,
which suggests the potential for thunderstorm activity in central
and east central Oregon and in the Blue Mountains during the day on
Friday and into Friday evening as well. Polan


.AVIATION...00Z TAFs...VFR will prevail over the next 24 hours at
all TAF sites. An approaching mid/upper level shortwave brings a
cold front, increasing cloud cover and lowering cloud bases late
tonight, but precipitation will be limited to OR/WA Cascade east
slopes and northern Blue Mountains overnight and Saturday morning.
Clearing skies from the west beginning mid-late Saturday morning
yielding sunny skies Saturday afternoon. Winds will be light through
remainder of this afternoon, becoming light drainage winds this
evening. Winds will increase toward daybreak through Saturday
morning becoming breezy by mid morning and persist through Saturday
afternoon. There will be a FROPA wind shift to westerly wind
direction as the cold front marches through eastern sections of
WA/OR an hour or two before daybreak. Expect sustained surface winds
of 15-22kt by 15Z at KDLS, KPSC, KPDT, KALW with gusts to 30kt late
morning through Saturday afternoon.  Polan


PDT  45  60  32  61 /  10  10   0   0
ALW  47  62  34  63 /  10  10   0   0
PSC  49  65  35  65 /  10   0   0   0
YKM  43  61  34  63 /  10  10   0   0
HRI  47  64  34  64 /  10   0   0   0
ELN  40  55  31  60 /  20  10   0   0
RDM  36  61  26  61 /   0   0   0   0
LGD  43  58  30  59 /  10  10   0   0
GCD  40  60  31  62 /  10   0   0   0
DLS  47  62  37  67 /  10  10   0   0




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