Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 302334 AAA
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
430 PM PDT Sun Apr 30 2017

Updated AVIATION Discussion

.SHORT TERM...Tonight through Wednesday. The cold front early this
morning has left gusty winds in its wake...and wind advisories for
the Kittitas Valley, the Simcoe Highlands and the Eastern Columbia
River Gorge look on track.  Gusts as strong as 50 mph have been
observed in these zones.  Elsewhere in the forecast area...winds are
gusting to 25-45 mph at this time. Showers have ended for most of
the area with the exception of the area northwest of Cle Elum where
showers associated with the Puget Sound Convergence Zone will
continue this evening. High pressure aloft will build overnight and
gradients will relax.  It will be chilly night with partly cloudy
skies...winds less than 15 mph...and temperatures in the upper 20s
to upper 30s. The upper level ridge will flatten once again on
Monday...allowing moisture and orographic lift to bring isolated to
scattered showers along the Cascades and the eastern mountains.
There should also be extensive mid and high level clouds in all
areas on Monday with little sun breaking through the cloud cover.
Despite the ridge building over the Pacific NW...broken to overcast
skies through Tuesday night will keep daytime temperatures from
climbing significantly and a warm night is forecast for Tuesday
night. There will also be a few Pacific fronts west of the Cascades
that will bring a slight chance to a chance of showers along the
east slopes of the WA Cascades. On Wednesday...the ridge axis will
be along the Cascade Range...and afternoon temperatures will climb
into the 70s to lower 80s (about 10-15 degrees above seasonal
average).  Wister

.LONG TERM...Wednesday night through Friday night...Mid/upper level
ridge of high pressure moving east Wednesday night with attendant
sinking motion yielding dry conditions through Wednesday night. The
ridge axis exits the region into Idaho/far western Montana by
daybreak Thursday. This puts forecast area on western flank of the
ridge and thus opens up the region to winds aloft backing to the
south during the day on Thursday allowing increasing moisture to
enter central and north central Oregon and south central Washington
on Thursday with moisture moving into NE Oregon Thursday afternoon.
The added moisture, in combination with daytime surface heating,
will produce an unstable airmass in the afternoon/evening for a
chance of showers and a slight chance of thunderstorms Thursday
afternoon and evening in the aforementioned areas. A mid/upper level
longwave trough approaches the coast on Friday and keeps the
interior Pacific Northwest in a deep southerly flow aloft and allows
a moisture plume ahead of the offshore trough to stream across the
region on Friday. Airmass again becomes unstable Friday afternoon
for scattered showers and a slight chance of afternoon/evening
thunderstorms in the eastern mountains of Oregon. Upper trough
reaches the coast Friday night allowing for a chance of showers
through Friday night.  Polan

Saturday morning through Monday morning...Although there are still
significant differences in model guidance for Saturday and  and
Sunday...overall consensus has trended toward a longwave trough over
the Pac NW deepening into a closed low and moving into central CA/NV
and cutting off through  the end of the forecast. The 12Z GFS has
adjusted significantly from previous runs and come much more into
line with the ECMWF and Canadian who have been advertising a similar
pattern evolution for the past few days. This feature will keep a
chance of showers in the forecast along our southeastern and eastern
borders as well as a slight chance for thunder along our eastern
border on Saturday.  Reasonable agreement for Sunday on the
development of a Rex block as the low continues to slowly shift
south...have gone with somewhat conservative high temperatures for
now for Sunday but if this comes to fruition may see some very warm
temperatures on Sunday. 74

&&

.AVIATION...00Z TAFs...VFR conditions will occur at all TAF sites
over the next 24 hours. FEW mid level clouds near 6K ft AGL until an
hour or two after sunset when skies should clear altogether and
remain clear through most of overnight before the next weak,
upstream system move through the upper level ridge and brings BKN
mid level clouds to TAF sites around daybreak tomorrow. Cloud bases
will lower a tad to 5K-7K ft AGL Monday afternoon. Sustained winds
will continue at 18-22 kts until around sunset and then diminish
through overnight. Weaker surface pressure gradients will occur on
Monday for sustained winds of 5-10 kts through Monday afternoon.
Polan

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  38  59  43  65 /  10  10  20  10
ALW  43  62  46  68 /  10  20  20  10
PSC  40  64  43  69 /  10  10  10   0
YKM  39  62  41  68 /  10  20  10   0
HRI  40  62  44  68 /  10  10  10   0
ELN  37  58  39  67 /  10  20  10   0
RDM  29  59  39  66 /  10  10  10  10
LGD  36  56  42  63 /  10  20  20  10
GCD  34  57  42  65 /  10  10  20  10
DLS  42  60  45  66 /  10  10  10  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 9 PM PDT this evening for ORZ041.

WA...Wind Advisory until 9 PM PDT this evening for WAZ024-026-521.

&&

$$

85/99/74/99


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