317 
FXUS66 KPDT 080954
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
254 AM PDT Fri Oct 8 2021

.SHORT TERM...Today through Sunday night...A longwave trough with
multiple embedded waves will be the primary influence of the
weather across the PacNW for the next 24 hours. The forecast area
is under a cyclonic flow aloft, and a strong wave riding down the
backside of the trough will bring precipitation to western WA/OR 
but not have an effect for the east side of the Cascades. Any 
precipitation today and this evening will be mainly east of the 
Blue Mtns and east of John Day where scattered showers are 
expected. This is associated with an upper low over northern CA 
pushing moisture and instability to far eastern Oregon. QPF 
amounts of 0.1-0.3 inch are forecast, and the Wallowa Mountains 
could have a couple inches of snow in the higher peaks. The threat
of thunderstorms is minimal and mainly over southeast Oregon. 
Skies will be partly cloudy today and temperatures will be near or
slightly cooler than yesterday.

The longwave trough will be forced eastward by an increasing
westerly flow off the eastern Pacific. A drier northwest flow 
tonight will bring clearing skies and chilly conditions. No Freeze
Warnings are planned at this time, as temperatures will be in the
mid to upper 30s across the Columbia Basin. Central Oregon and 
the Grande Ronde Valley have already observed a hard freeze this 
season. The John Day Basin will be flirting with near freezing 
temperatures.

The weak shortwave ridge will maintain dry conditions Saturday,
and near seasonable temperatures will make for a pleasant day for
outdoor activities. The next system to arrive Saturday night and
Sunday will bring scattered to numerous showers over the
mountains, but rain shadowing is likely off the Cascades with only
isolated to scattered showers over most of the Columbia Basin 
down to central Oregon. Winds aloft will increase significantly on
Sunday, and isentropic descent will bring 20-30 knot winds to the
surface...possibly up to 40 knots. The NBM would support this 
with gusts at 30-35 mph in the meteograms at various stations in
and around the Columbia Basin. QPF amounts are not impressive for
Sunday and Sunday night with mostly up to 0.25 inch expected. 
Snow levels will fall to near 3500 feet Sunday night, but the 
precipitation will taper off overnight as well. However, some of 
the mountain passes may see light accumulations of snow for the 
first time of the season. The crest of the WA and OR Cascades 
could have 1-3 inches of new snow, including White Pass and Mt. 
Bachelor. Wister/85

.LONG TERM...Monday through Friday...The long term will be
mostly a troughy pattern through the work week as the deep low
bringing the strongest shot of cold air across our region yet for
this fall moves towards the Four Corners and then the Central US,
followed by a pair of weaker troughs moving just north of us over
the week before some ridging may finally settle in just beyond the
long term forecast period.

An upper level low will be over the CWA to begin the long term, 
deepening and descending towards the Four Corners region through 
Tuesday. The primary weather feature with this low will be the 
notably colder air associated with it, as much of the region drops
below 40 degrees for overnight lows Monday into Tuesday. Freeze
warnings will be likely for a notable portion of the CWA aside
from the Columbia Basin/Gorge. Then, during the middle through 
end of the work week, a pair of weaker troughs associated with a 
low that's moving from the Gulf of Alaska into Canada, will move 
north of us. These should mostly bring precipitation that will 
cutoff at the Cascades, but some breezy to gusty winds may be 
possible Wednesday through Friday. Otherwise a steady increase in 
temperatures through the week is likely after the cool off, with 
highs on Friday about 5 to 10 degrees warmer than Monday.

At this point in the forecast, ensembles are lining up well on the
placement of the main low early next week, with the remaining 
question the strength and depth of the system as it moves towards 
the Four Corners. With multiple days of forecasts all but 
confirming our expected cooldown, it's unlikely major changes will
occur and our first widespread freeze of the season should occur
Tuesday morning. Goatley/87

&&

.AVIATION...(previous discussion)...vfr conditions are expected to continue across all taf 
sites for the next 24 hours. However a weather system may increase 
mid level clouds and some showers could near taf sites kpdt and kalw 
between 15z to 18z.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  60  36  63  44 /  10   0   0  10 
ALW  62  40  64  48 /  10   0   0  10 
PSC  65  41  67  51 /   0   0   0  20 
YKM  63  35  65  43 /   0   0   0  20 
HRI  65  39  66  48 /   0   0   0  10 
ELN  62  37  61  43 /   0   0   0  30 
RDM  60  29  62  35 /   0   0   0  10 
LGD  59  33  59  38 /  20  10   0  10 
GCD  62  32  61  37 /  20   0   0  10 
DLS  66  42  66  49 /   0   0   0  20 

&&

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

$$

SHORT TERM...85
LONG TERM....87
AVIATION...97