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Area forecast discussion 
National Weather Service Pendleton or
1028 am PDT Thursday Sep 18 2014

Updated aviation discussion

Update...the current forecast remains on track with just a few
minor adjustments to the today and this evening period. Have made
some minor adjustments to the highs today...mainly across the
western portion of the County Warning Area.

Expect windy conditions along the Kittitas Valley and the Columbia
River gorge today...with the basin and foothill areas being breezy.
Expect 20 miles per hour gusting to 30 miles per hour for The Gorge and the kittias
valley...with 15 miles per hour gusting 25 miles per hour elsewhere across the basin.
Winds should begin to pick up after noon today...and are expected to
be strongest around 5 PM diminishing after midnight.

Have also pulled back on probability of precipitation to go mostly slight chance east of the
Cascade crest. The split flow will cut off most of the moisture
from the trough that will progress south along the California coast
today into tonight. Slight chance upslope showers can be expected
across the northeast mountains today and this evening. Have
mentioned slight chance thunder across the northeast mountains
through 5 PM...as it still can't be ruled out. But once the west
northwest flow sets in this evening...instability will be very
limited. So have pulled back on the thunder potential to just The
Eagle caps...southern Grant...Crook...and Deschutes County from 5 to
8 PM this evening. Weber

Aviation...18z tafs...VFR conditions are expected to persist
through the next 24 hours. There may be some light showers around
the region today with the remote possibility of a thunderstorm at
krdm and kbdn in the afternoon and evening...then partial clearing
overnight. Westerly winds will be increase slightly today at 10 to
20 miles per hour then decrease overnight.

&&

Previous disc... /issued 255 am PDT Thursday Sep 18 2014/

Short term...today through Saturday night...an upper level trough
is near the coast as it slowly shifts eastward. The trough is
splitting as it moves inland with the northern section in Washington
and the southern section in California. There are two bands of
precipitation on radar and models. One is near the Cascades on the
east side of the trough axis and the second one is in eastern Grant
County...Wallowa County...and Baker County. Hrrr shows the first
band remaining in central/north central Oregon and central
Washington this morning. The second band is associated with a jet
streak. Hrrr shows this band remaining separate and moving northeast
out of the Oregon by 16z. The morning forecast has the two separate
bands...then the first band will spread across central to northeast
Oregon as the trough axis moves across eastern Washington and Oregon
this afternoon. The best instability will move from central to
northeast Oregon where the diffluence from the splitting trough is
added to the instability ahead of the trough. Isolated thunderstorms
may develop in this region during the afternoon and early evening.
The trough axis will be in Idaho by 6z/2300 PDT with rain showers
ending except for orographic showers near the Cascade crest. Friday
and Saturday the upper level ridge will build over the Pacific
northwest with clearing skies and warming daytime temperatures.
Coonfield

Long term...Sunday through Wednesday...00z model runs indicate very
similar solutions over forecast area and northeast Pacific with a
middle/upper level ridge of high pressure continuing over the Pacific
northwest Sunday and Monday. Models show consistent solutions for
Tuesday as well with the ridge moving east into the northern plains
by daybreak Tuesday as the next longwave trough spreads eastward to
130-140w. The GFS is more progressive in taking the axis of an open
longwave trough to 132w by Tuesday afternoon whereas the European model (ecmwf) keeps
the lowest heights in the overall trough near 140w where a closed
low with much lower heights develops in the European model (ecmwf) solution. Both GFS
and European model (ecmwf) show a very weak disturbance moving through forecast area
Monday night and Tuesday so I have increased probability of precipitation a tad to slight
chance for possible isolated light showers in the Blue Mountains
Monday night and Tuesday. The trough approaches the coast Tuesday
night and spreads increasing clouds, moisture, and rain to the
Cascades just before daybreak on Wednesday. The precipitation
spreads across forecast area Wednesday morning. As already
mentioned, the GFS is faster in terms of bringing the trough axis to
the coast by late Wednesday morning while the European model (ecmwf) keeps the trough
axis well offshore. This phasing difference between the two models
on Wednesday with respect to the placement of the trough axis
results in the European model (ecmwf) taking longer to spread rain to the Blue
Mountains until late Wednesday night or Thursday morning. As such
have lower confidence in pop forecast for Wednesday in the eastern
sections of forecast area. Polan




&&

Preliminary point temps/pops...
PDT 80 55 80 52 / 20 10 0 0
alw 83 61 80 57 / 20 10 0 0
psc 85 57 85 51 / 10 10 0 0
ykm 80 56 84 54 / 20 10 0 0
hri 83 55 85 48 / 10 10 0 0
eln 80 57 83 52 / 20 10 0 0
rdm 76 43 79 40 / 20 20 0 0
lgd 81 51 79 44 / 20 10 0 0
gcd 78 49 81 47 / 20 10 0 0
dls 78 58 83 52 / 30 10 0 0

&&

PDT watches/warnings/advisories...
or...none.
Washington...none.
&&

For additional weather information, check our web site at...
www.Weather.Gov/Pendleton

$$

89/99/99

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