Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 260522
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1022 PM PDT Sun Jun 25 2017

Updated aviation discussion

.SHORT TERM...Tonight and Monday...Southerly flow has kicked in
around the ridge of high pressure allowing moisture from northern
California to advect into Oregon this evening. This has led to the
development of isolated thunderstorms creeping into central Oregon
with some gusty winds and light rain. This moisture will continue to
move across the forecast area overnight but expect thunderstorm
activity to remain close to the Cascades possibly reaching up into
the Mount Adams area before thunderstorms stop overnight. Moisture
will be in place ahead of the remnants of the upper level low
pressure off the coast of California that will pass over the
forecast area. This will lead to the development of more
thunderstorms Monday afternoon mainly south of a lie from The Dalles
to Pasco. There is a chance that some of the thunderstorms could
become strong to possibly severe across central to northeast Oregon
Monday afternoon through evening. The thermal trough will be over
the forecast area tonight combining with the increasing cloud cover
to produce a very warm night. Will see some increasing westerly
winds Monday afternoon coming over the Cascades which will usher in
some cooler air for the western portion of the forecast area but the
eastern portion will remain hot, similar to today.

.AVIATION...06Z TAFs...Generally VFR conditions are expected for the
next 24 hours but there will be convection to deal with. Convection
is decreasing overnight but leaving considerable mid and high level
clouds over the region. This will break up overnight but then
another round of convection is likely Monday afternoon possibly
impacting sites KRDM, KBDN, KPDT and KALW. Will also see increasing
westerly winds Monday becoming 10-20 kts in the afternoon and
evening.



&&

.PREV DISCUSSION... /issued 245 PM PDT Sun Jun 25 2017/

SHORT TERM...Tonight through Wednesday...Models in pretty good
agreement on trends through Wednesday. A brief stretch of active
and unsettled weather will hit mainly eastern Oregon tonight through
Monday night. Satellite/radar to show moisture moving moving north
and thunderstorms developing in southern Jackson County. A few
lightning strikes were detected in the past hour over extreme
northern CA. Expect this moisture to continue moving north and
affect mainly Deschutes county near the Cascades this evening.  Very
warm temperatures will continue overnight with this unusually warm
airmass, especially where clouds move in and slow the outgoing heat
loss. An upper level low
offshore will transition to a trof and push across area Monday
and overnight. Best moisture/instability will continue over
central and NE oregon south of a line from Madras to Walla Walla.
With the dry air in the lower levels we could see gusty outflow
winds with some of these storms.  The trof passage will return a
more stable westerly flow with modified marine air. Gusty
winds will be noted in some areas, especially over north central OR
and the Kittitas Valley. Temperatures Tuesday and Wednesday will
average near to slightly above normal.

LONG TERM...Wednesday night through Sunday night...A mid/upper
level ridge of high pressure in the NE Pacific near 130W Wednesday
evening will be migrating eastward toward the coast overnight with
the ridge axis arriving on the coast Thursday evening. The region
from the Cascade crests to the Idaho border will be on the eastern
flank of the ridge during the day on Thursday for dry/stable
conditions. The ridge axis moves directly over the interior Pacific
Northwest on Friday thus continuing dry and stable conditions.

Models are advertising a basically zonal flow aloft over the
interior Pacific Northwest as well as over marine environs
immediately offshore by virtue of a flat ridge upstream in the NE
Pacific through the remainder of the period.

Differences did appear in the 12Z model runs for Saturday night and
Sunday with the ECMWF indicating a mid/upper level trough undergoing
amplification as it digs SE and across the region Saturday night and
Sunday, but QPF amounts were restricted to the WA/OR Cascade crests
with this ECMWF run. The 12Z GFS and Canadian runs show the westerly
flow aloft persisting over the region and upstream over the NE
Pacific, due west of the coast. This mid/upper pressure pattern
would produce sinking air east of the Cascades for dry conditions. I
discounted the ECMWF model for the weekend forecast and went with
the GFS and Canadian models, which show dry and stable conditions
through the weekend.  Polan


FIRE WEATHER...Will continue the current Red Flag Warning for
zones 640/641/675 for Haines level 6 and low RH until 11 PM.
Isolated thunderstorms will be possible across Central Oregon
tonight, but with coverage limited and RH`s increasing by the time
any convection does develop, no significant fire weather threat is
expected. On Monday, scattered to numerous thunderstorms will
develop in Central Oregon by early afternoon, spreading to the east
by late afternoon/evening. With abundant lightning expected, along
with the potential for outflow winds, have upgraded the Fire Weather
Watch to a Red Flag Warning for zones 640 and 644. In addition,
breezy to locally windy conditions will develop further north across
the Columbia Basin and Gorge. However, with RH`s increasing from
this weekends very low readings, will not issue any watches or
warnings for now. Periods of breezy conditions can be expected
Tuesday and Wednesday, but duration of low RH`s look marginal for
headlines.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  66  93  59  82 /   0  20  30   0
ALW  71  96  64  85 /   0  20  30  10
PSC  67  97  62  88 /   0  20  20   0
YKM  68  97  59  87 /  10  10  10   0
HRI  67  95  60  85 /   0  20  20   0
ELN  66  93  56  83 /  10  10   0   0
RDM  59  90  48  83 /  20  20  10   0
LGD  59  94  56  81 /   0  40  40  10
GCD  62  95  55  83 /   0  50  40  10
DLS  69  89  61  82 /  20  10   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 11 AM to 10 PM PDT Monday for ORZ640-644.

     Red Flag Warning until 11 PM PDT this evening for ORZ640-641.

WA...Red Flag Warning until 11 PM PDT this evening for WAZ641-675.

&&

$$

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