823 
FXUS66 KPDT 081750 AAA
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
1050 AM PDT Fri Oct 8 2021

Updated aviation discussion

.SHORT TERM...Today and Tonight...A long wave trough continues to 
impact the forecast area today with some showers over the eastern 
portion. This trough is split with the southern portion moving into 
California and sending some moisture across far eastern oregon this 
morning in the form of isolated to scattered showers. The northern 
portion is sliding down the coast and will consolidate with the 
southern portion to form a closed low over the Great basin on 
Saturday. The northern portion will have little impact to the 
forecast area other than some clouds. Overall the trough shifts 
eastward late tonight and Saturday allowing a temporary ridge of 
high pressure move into the region. Clearing skies will allow for 
some freezing temperatures in the upper John Day Basin so have 
issued a freeze warning for overnight through early Saturday.

&&

.AVIATION...18Z TAFs...VFR conditions are expected for the next 24 
hours. A few showers will continue through this afternoon from the 
Blue Mountains eastward but should not affect ALW or PDT. Most TAF 
sites will have FEW-SCT clouds at 7K-10K feet AGL today then skies 
will clear this evening and overnight. Winds will remain below 10 
kts aside from DLS which will have northwest winds of 10-15 kts with 
gusts to 20 kts this afternoon. 83

&&

.PREV DISCUSSION... /issued 417 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

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  61  36  63  44 /  20   0   0  10 
ALW  62  40  64  48 /  20   0   0  10 
PSC  66  40  67  51 /  10   0   0  20 
YKM  63  35  65  43 /   0   0   0  20 
HRI  66  37  66  48 /  10   0   0  10 
ELN  61  37  61  43 /   0   0   0  30 
RDM  61  27  62  35 /   0   0   0  10 
LGD  58  34  59  38 /  30  20   0  10 
GCD  60  31  61  37 /  20   0   0  10 
DLS  67  42  66  49 /   0   0   0  20 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Warning from 2 AM to 9 AM PDT Saturday for ORZ505.

WA...None.
&&

$$

SHORT TERM...91
LONG TERM....91
AVIATION...83