Area Forecast Discussion
Issued by NWS Pendleton, OR

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336
FXUS66 KPDT 241745 AAA
AFDPDT

Area Forecast Discussion...Update
National Weather Service Pendleton OR
1045 AM PDT Wed May 24 2017

Updated Aviation Discussion

.SHORT TERM...Today through Thursday...An upper level low
will continue passing to the north of the forecast area creating
windy conditions through this evening along with cooler temperatures.
The low will depart to the east tonight but leave the area under an
upper level trough pattern in a northerly flow. A shortwave dropping
south in this flow will increase instability across portions of the
forecast area with increasing chance of showers and possible
afternoon and evening thunderstorms.

&&

.AVIATION...18Z TAFs...An upper low will continue to move east
across the Canadian Prairie provinces through the next 24 hours. The
upper level flow over the Pacific Northwest will turn northerly by
Thursday morning. This will allow a disturbance to swing across the
region tonight into Thursday. Conditions will mainly be VFR through
the period, though may see some clouds between 2000 and 3000 ft AGL
at KRDM and KBDN late in this period. Will keep these lower clouds
SCT at these two sites for now. Will see increasing clouds over
KPSC, KALW and KPDT with lowest bases around 7-8000 ft AGL. Winds
will continue to be breezy with sustained speeds running between 14
and 24 kts into this evening. Wind directions will mainly be
westerly and northwesterly. 90

&&

.PREV DISCUSSION... /issued 300 AM PDT Wed May 24 2017/

SHORT TERM...Today through Friday...Water vapor imagery shows a
trough moving into the area with an upper low moving southeast along
the Canadian Rockies towards northern Washington. A cold front is
just about ready to move into Idaho. The front is very moisture
starved and there has been no precipitation and few if any clouds.
The main impact is increased winds though some areas are having a
lull during the overnight hours. Ellensburg airport continues to
have northwesterly winds at 25 to 35 mph with gusts to 45 mph so
current wind advisory for Kittitas county looks good. The rest of
the area will have west to northwest 15 to 30 mph winds with gusts
to 35 mph through this afternoon. Do not think winds will reach
advisory levels elsewhere, though it could be close for a few hours
this afternoon in the Columbia Gorge, Columbia Basin and Blue
Mountain Foothills. The other main impact will be temperatures as
high temperatures today will be around 20 degrees cooler than
yesterday. Highs will be in the upper 60s to mid 70s with upper 50s
to mid 60s in the mountains. Tonight the upper low will move rapidly
east into Manitoba but the trough will remain over our area with a
northwest flow. Models show some moisture moving in this evening and
a slight chance of showers developing in the Washington Cascades and
eastern Oregon mountains in the late night and Thursday morning
hours. A wave and instability under the trough will create a slight
chance of showers and thunderstorms Thursday afternoon in the
Cascades and from the Blue Mountain Foothills and Ochoco-John Day
Highlands eastward. Do not expect any strong or severe
thunderstorms. Rain amounts will be light and just a few hundredths
of an inch in general. Showers will taper off in northeast Oregon
during the evening. The trough will drift slightly eastward Thursday
night and Friday and an offshore ridge will begin to build ashore.
There will still be a moist northerly flow over the eastern half of
the area and there will be a slight chance of showers and
thunderstorms Friday afternoon over the northern Blue mountains and
Wallowa county while the rest of the area is dry. Temperatures
Thursday will warm a couple of degrees to the lower to mid 70s with
mainly 60s in the mountains. Friday will be in the mid 70s to lower
80s with mid 60s to lower 70s in the mountains. Perry

LONG TERM...Friday night through Wednesday...GFS and EC models in
good agreement. Both show upper level trof in ID with residual
moisture and instability over the eastern mountains Friday evening.
Upper level ridge builds over the area during the weekend with above
normal temperatures and dry stable conditions.  A southwest flow
will return enough moisture for the slight chance of thunderstorms
again Monday afternoon and also Tuesday and Wednesday afternoons.
Upper level ridge combined with weak surface pressure gradient will
keep winds light through the period. About the only impacts will be
the much above normal temperatures resulting in high level snowmelt
and increase runoff into some of the streams coming off the
Cascades. 79

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  67  43  67  46 /   0   0  20  20
ALW  70  47  70  51 /   0   0  20  20
PSC  74  46  75  49 /   0   0  10  10
YKM  73  46  76  49 /   0   0  10  10
HRI  72  45  72  47 /   0   0  10  10
ELN  66  43  73  47 /   0   0  10  20
RDM  69  35  70  38 /   0   0   0  10
LGD  63  40  63  41 /   0  10  20  20
GCD  67  40  67  42 /   0   0  20  20
DLS  69  47  78  51 /   0   0  10  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory until 10 PM PDT this evening for WAZ026.

&&

$$

91/83/90



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