Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 231758 AAA
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
1057 AM PDT Sun Apr 23 2017

Updated AVIATION Discussion

.UPDATE...A weak weather system is moving through the eastern CWA at
this time and is beginning to exit the area. There were a few light
showers or sprinkles over the forecast area, but they have mostly
moved off to the east. The next system will quickly move into the
CWA by this afternoon with a chance of showers except rain and
higher mountain snow showers in the eastern mountains and near the
crest of the Cascades of both Oregon and Washington. There will be
locally breezy winds by this afternoon and early evening...but winds
will not exceed 15 to 25 mph and the strongest winds will be over
the ridge tops of the hills from central Oregon north to the Lower
Columbia Basin, Yakima and Kittitas valleys. It will be cool today,
due to cloud cover and expected precipitation, with below normal
temperatures. The weather pattern will remain wet and unsettled as a
moist Pacific weather system slowly moves east into the Pacific
Northwest. This will result in a mostly wet week...at least the
first half of the week. Temperatures will be below normal with snow
levels dropping to 3500 to 4500 feet by Tuesday. As such there will
be some snow over the higher mountains and passes. Will have to
monitor this for the possible need of winter highlights for
snow above elevations of 3500 to 4500 feet. 88

&&

.AVIATION...18Z TAFs...VFR conditions through the next 24 hours.
15-20 degree dewpoint spreads in the boundary layer at TAF sites
point to a very dry airmass in lowest layers above ground thus
yielding cloud bases AOA 5000 ft AGL through this evening followed
by cloud bases lowering to BKN040 by 12Z. Sustained winds increasing
through this afternoon to 10-15 kts with gusts to 21 kts, then
diminishing through tonight to 5-10 kts.  Polan

&&

.PREVIOUS DISCUSSION... /issued 440 AM PDT Sun Apr 23 2017/

SHORT TERM...Today through Tuesday...A west-northwest upper level
flow will develop today the eastern Pacific and the Pacific
Northwest, then continue through the remainder of this period. A
disturbance moving into northern California this morning will move
across the region today. Thus will see an increase in chances of
showers late this morning into this afternoon. May be enough
instability for a stray thunderstorm over southern Wallowa county
this afternoon. A stronger system within this upper level flow will
move into the region Monday. Thus expect scattered to numerous
showers over the area. This precip will keep high temps Monday well
below seasonal. Instability over portions of the eastern mountain
zones will be strong enough for a few afternoon thunderstorms.
Tuesday will see a break and a decrease in shower chances as the
region will be between the Monday system and another system expected
Tuesday night. 90

LONG TERM...Tuesday Night Through Saturday...Models are in good
agreement that a moist west to northwest flow will be over the
region Tuesday through Thursday. The moist westerly flow will allow
a series of weather systems to impact the WA and OR with showers,
occasionally breezy conditions, and  cooler than normal
temperatures. Rain shadowing will limit pops in the lower Columbia
Basin, Yakima and Kittitas Valleys, and Deschutes Plateau. Thursday
night through Saturday an upper level ridge will build offshore and
slowly shift east to the coast. Showers will decrease Thursday night
and Friday as an upper level trough moves into ID. Dry conditions
will prevail by Saturday as the building ridge influences WA and OR.
Coonfield

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  39  55  39 /  30  40  60  40
ALW  60  43  57  43 /  50  40  60  50
PSC  67  44  61  43 /  20  30  60  30
YKM  64  39  60  38 /  30  30  50  20
HRI  65  41  59  40 /  20  40  60  30
ELN  59  37  57  38 /  30  30  40  20
RDM  55  33  53  33 /  30  40  70  40
LGD  56  36  51  37 /  60  60  70  70
GCD  57  37  52  36 /  60  60  80  60
DLS  61  42  57  43 /  40  50  70  50

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

88/99/90/76



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