470 
FXUS66 KPDT 061736 AAA
AFDPDT

Area Forecast Discussion...Updated 
National Weather Service Pendleton OR 
1037 AM PDT Wed Oct 6 2021

Updated aviation discussion

.MORNING UPDATE...Visible satellite imagery showing a cold front 
pushing east across the forecast area, currently settling in over 
the eastern mountains. Light showers producing a couple hundredths 
of an inch have been reported this morning, with any rain or high 
mountain snow expected to move out of the CWA by the late morning. 
Clear skies are visible behind this front, where cooler temperatures 
will prevail this afternoon. Highs in the mid 50s and 60s expected 
across most areas, with some breeziness expected primarily along the 
east slopes of the Cascades. SW flow aloft will prevail behind the 
front, so some high clouds may build towards the evening, but 
otherwise expecting much of Wednesday to be clear. Current forecast 
looks to be on track, with only minor adjustments to precip and 
temps made. 74

&&

.AVIATION...18Z TAFs...VFR conditions expected over the next 24 
hours. A few light showers continue east of the Blue Mountains and 
will move east out of the area in the next few hours. Skies have 
cleared rapidly behind the departing cold front this morning. Expect 
generally clear skies through tomorrow morning aside from FEW high 
cirrus clouds tonight. Winds will increase this morning and 
afternoon to 7 to 15 kts before decreasing to around 5 kts tonight. 
KDLS will have gusts to 20 to 25 kts this afternoon. Perry/83

&&

.PREV DISCUSSION... /issued 429 AM PDT Wed Oct 6 2021/ 

SHORT TERM...Today through Friday night...A longwave trough
currently resides west of the Continental Divide with the axis of
the trough along the west coast. There are two frontal bands of
showers embedded in the southerly flow aloft over the forecast 
area...one band along the WA/OR Cascades and a lesser organized 
band over the northeast mountains. Precipitation amounts so far
have been less than a tenth of an inch east of the Cascades.
Precipitation will taper off later this morning when the trough
shifts eastward and a drier west-southwest flow aloft takes over.
Any showers this afternoon will be widely scattered and east of 
the Blue Mtns and along the WA Cascades. There may be a light 
dusting of snow between 5000-6000 feet and up to 0.5 inch of snow 
above 6000 feet today. A fairly tight pressure gradient is causing
breezy winds over portions of the forecast area, and this will 
likely continue for most of the day. Today's highs will be about 
15-25 degrees cooler than yesterday with highs in the 50s to mid 
60s.

The longwave trough will split overnight, and WA/OR will be under
a dry westerly flow associated with the northern branch while the
southern branch strengthens off the CA coast. A chilly night is 
in store as skies will be clear to partly cloudy and temperatures
will fall into the mid 20s to mid 30s (35-40 in the Columbia 
Basin). A freeze watch was issued for Central Oregon and will also
include the Grande Ronde Valley. While confidence is high that 
these zones will be quite cold tonight, the one fly in the 
ointment will be the high level clouds that could keep lows just 
above freezing for some locations. Rather than jumping into a 
freeze warning, will keep the watch and determine how much cloud 
cover to expect and have a better feel for overnight lows.

A wave sliding down the backside of the trough will cause the
westerly flow to buckle Thursday through Friday. Thursday will
continue to be a dry and cool day with a weak cyclonic flow over
the area. The deterministic models and the HREF members keep 
showers over southeast Oregon on Thursday. On Friday, the 
shortwave will travel east of the Cascades for a slight chance of 
showers over the eastern mountains/valleys. The NAM is the only 
model that shows very little QPF, but the other models hint at 
some light QPF over southeast Oregon and as far north as the Eagle
Caps and Elkhorns. Locally breezy winds are also expected on 
Friday, mainly in the Grande Ronde Valley near North Powder and
the John Day Basin. Wister

LONG TERM...Saturday through Wednesday...The long term will be
characterized by a brief round of ridging across our area on
Saturday, helping to bring a slight increase in temperatures
through the weekend, followed by a strong and deep low that will
produce gusty conditions and the coldest temperatures since last 
winter into spring, with even a chance at some mountain snowfall.

Saturday a ridge will be over the region as the trough that 
impacted our area late in the week departs, with another system 
right behind it. This will allow us one calm/fair day in regards 
to the pattern, with mostly clear skies and temperatures into the
60's. Overnight into Sunday, a deep low will begin to overspread 
our region from the northwest, bringing cloud cover and then gusty
winds. Temperatures should remain mild, in the 50's to 60's. As
temperatures drop Sunday evening, high elevations of the Cascades
may begin to see light snow, with a chance of showers otherwise
for the rest of the area. Then, as the upper low moves across our
area, we're expected to remain in a troughing pattern through all
of next week as this strong system descends across and down into 
the Four Corners, then across towards the Central US. Temperatures
will plummet behind a cold front Sunday into Monday, with 
widespread lows Monday night into Tuesday in the 20's to 30's, 
causing freezes to be expected across nearly the entirety of the 
forecast area except for the Columbia Basin and along the Columbia
River into the Gorge. A light chance of showers is possible Monday
evening, with light mountain snowfall as snow levels descend
below 3000 ft. Then under a troughing pattern into the middle of 
next week, cool temperatures for highs in the 50's to low 60's 
are likely, with a weak trough bringing scattered precipitation 
yet again Tuesday into Wednesday.

Ensembles remain in agreement on the likelihood of this system and
its impacts, but there is some disagreement on the strength and
placement. Cluster analysis for Monday all show the system over
our region, with variance in the strength. Thereafter, models
diverge on how far southeast of our region the low can make it, as
well as how deep it can become. Regardless of these outcomes, a
notably cooler than average pattern remains on track for our area,
with areas of much needed precipitation also likely. Goatley/87

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  60  35  59  36 /  20   0   0   0 
ALW  62  39  62  39 /  20   0   0   0 
PSC  66  40  63  40 /  20   0   0   0 
YKM  63  34  62  34 /  10   0   0   0 
HRI  64  38  63  38 /  20   0   0   0 
ELN  60  35  60  34 /  10   0   0   0 
RDM  57  28  59  31 /  10   0   0   0 
LGD  53  32  59  35 /  20   0   0   0 
GCD  57  32  63  37 /  30   0   0   0 
DLS  64  42  65  42 /  10   0   0   0 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Watch from late tonight through Thursday morning for 
     ORZ049-511.

WA...None.
&&

$$

SHORT TERM...74
LONG TERM....87
AVIATION...83