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fxus66 kpdt 132214 

Area forecast discussion
National Weather Service Pendleton or
214 PM PST Tue Nov 13 2018

Short term...tonight through Friday...upper level ridge
currently overhead will continue to flatten ahead of an
approaching frontal system this evening. Patchy fog is expected to
return to the basin this evening with loss of heating, but with
increasing west-southwesterly flow aloft with downslope off the
Cascades, and to a lesser extent the southern blues may curtail
coverage in their immediate vicinity. Weak warm air advection
ahead of the approaching frontal system early Wednesday morning
will spread precipitation chances across the Washington Cascades
and adjacent valleys. With snow levels rising through 4000 to 5000
ft across this area Wednesday morning do not expect any
significant snow impacts, however, cold air in Cascade valleys
will result in a chance of light freezing rain for areas like
Snowden, US-12 near Rimrock, sunrise-410 near Cliffdell and I-90 near
Cle Elum for a few hours Wednesday morning until surface
temperatures rise above freezing. A bulk of the cold air
advection with the aforementioned cold front slides north of the
area Wednesday night/Thursday morning and looks unlikely to
completely scour out the near surface inversions across the
Columbia Basin, so will keep at least a mention of some patchy
morning fog there. Given somewhat weaker inversions/thinner
potential stratus coverage with the flattening upper ridge have
trended the Max temps in the basin toward a middle ground
representing a partial breakout to sunshine during the afternoon.
Temperatures away from the basin will continue to see fairly wide
diurnal swings with lows in the upper teens to lower 20s and highs
in the 50s. A backdoor cold front drops south across the area
Friday and this should serve to scour out any remaining
fog/stratus across the basin as well as bringing rain chances to
the wallowas and blues/foothills early Friday morning. Snow levels
with the front are around 6000 ft so do not expect any snow other
than on the highest peaks of the wallowas. Breezy gradient driven
winds will continue in the Ladd/pyles canyons near La Grande
through early Wednesday. Peck

Long term...Friday night through Tuesday. A dry northerly flow
aloft will follow the backdoor cold front on Friday. Rain and high
elevation snow showers over eastern or and far southeast Washington on
Friday evening will end by midnight. High pressure will rebuild for
a dry and stable weekend. Fog, freezing fog and low clouds will
return and will blanket the Columbia Basin and surrounding valleys
with a potential for patchy fog in the mountain valleys. The 12z GFS
and European model (ecmwf) are flatter with the ridge (12z Canadian maintains a high
amplitude ridge) compared to the previous runs and advertise a weak
shortwave Sunday night. The latest GFS introduces light
precipitation across south central Washington and north central or while the
European model (ecmwf) is much weaker with the shortwave and shows no precipitation.
Will keep Sunday night dry for now but the upcoming shifts may
decide to add slight chance pops if future models come into
agreement. The ridge will completely flatten and shift eastward
Monday night and Tuesday. This will allow a low pressure trough
offshore to move inland and spread precipitation east of the
Cascades on Tuesday. The European model (ecmwf) is slower with the breakdown of the
ridge and the shift to a southwest flow aloft compared to the GFS,
but both models would indicate a good chance of rain and high
elevation snow Tuesday night. Wister


Aviation...00z tafs...visibilities have generally improved this
afternoon with modest heating despite low stratus. This will
likely prevail through sunset. Thereafter, stratus will slowly
settle with fog and freezing fog development expected again
overnight. This will lead to another night of IFR/LIFR ceilings
and visibilities for terminals east of kbdn/krdm. Variable winds
of 8 knots or less will prevail through the period.


Preliminary point temps/pops...
PDT 27 47 37 48 / 0 0 0 0
alw 28 44 39 49 / 0 0 0 0
psc 27 43 33 49 / 0 0 0 0
ykm 26 42 31 49 / 10 10 0 0
hri 28 42 35 51 / 0 0 0 0
eln 23 44 33 49 / 10 20 10 0
rdm 24 58 26 56 / 0 0 0 0
lgd 29 50 34 54 / 0 0 10 0
gcd 31 55 35 55 / 0 0 0 0
dls 33 48 38 53 / 0 10 10 0


PDT watches/warnings/advisories...
Washington...air stagnation advisory until 1 PM PST Friday for waz027.

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