379 
FXUS66 KPDT 162319
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
419 PM PDT Sun Oct 16 2022

Updated Aviation Discussion

.SHORT TERM...Tonight through Tuesday night... Rather dry and
benign conditions persist into the middle of the week as a 
strong area of high pressure remains planted over the inland 
Pacific Northwest. The next several days the western US shifts 
into a stable ‘Rex Block’ pattern with an upper-level high 
pressure centered over central Idaho accompanied by a developing 
cut-off low off the coast of southern California. This translates 
locally to dry and calm weather continuing as daytime temperatures
rise well above normal into the 70s to near 80 Monday and Tuesday
for a large portion of the region. Compared to climatology, high 
temperatures are set to run 10-20 degrees above normal with the 
greatest abnormalities found in the mountain areas. Unfortunately 
these dry conditions, warm temperatures, and low afternoon RHs in 
the 10s to 30s will keep wildfire season persisting a bit longer 
until we can get a good shot of fall-like precipitation. At the 
very least, winds don’t appear particularly noteworthy during this
time period due in-part to weak surface pressure gradients under 
the high pressure. 

Beyond abnormally warm daytime conditions, overnight low
temperatures tonight through Tuesday night remain a little 
closer to normal and in some cases potentially nudge a few degrees
below normal. Clear skies in combination with light winds will 
allow for very efficient radiative cooling in many of the mountain
valley locations as cooler air pools off nearby terrain and the 
boundary layer decouples. This process is likely aided by drying 
in the mid- level as well with most models like the HREF and 
GFS/NAM depicting a slight decrease in overnight dew-points 
tonight onward compared to the past several nights. Locations like
Sunriver/La Pine, Seneca, La Grande, and Cle Elum, likely drop 
around or below freezing while the Columbia Basin sees lows in the
upper 30s and 40s. It’s worth noting confidence is still low 
regarding zone-wide freezing temperatures which besides the Grande
Ronde Valley have yet to be observed so have held off issuing any
freeze warnings for this forecast cycle. 99 

.LONG TERM...Wednesday through Sunday...The main sensible weather
highlight revolves around the breakdown of a blocky upper-level 
ridge Friday-Saturday that will prompt a pattern change. 
Confidence is high at this point (90%) that there will be a change
away from unseasonably warm temperatures. Current thinking is 
this will correspond to breezy to locally windy conditions, more 
seasonable to slightly below normal temperatures, and potential 
for beneficial rainfall this weekend as an amplified upper trough 
digs southeast into the Northern Intermountain West and Central 
Great Basin ridge. There are increasing odds (at least 40% or 
more) for beneficial rain of a 0.25” or more falling across and 
over the high slopes of the Cascades, Blues, and parts of the 
central OR mountains. Meantime, lower elevations will see the 
possibility (30%) for a tenth of an inch or more. 

Prior to this feature, fair and dry weather with highs 10-15
degrees above normal in tandem with light breezes will continue to
prevail Wednesday and Thursday. The large scale pattern early
Wednesday will be characterized by an upper ridge centered over
eastern WA/OR extending into the Northwest Territories. Generally
quiet weather in this time period, though a weak shortwave trough
embedded in the flow will move through early Thursday night will
prompt increasing clouds, at least partly cloudy. Otherwise, high
valleys and other colder climo-prone areas will see near or sub-
freezing temperatures Wednesday and Thursday AM. 

While weak ridging fills in early Friday, ensemble systems are
showing good agreement in an upper trough at this time in the Gulf
of Alaska evolving north of Vancouver Island Friday and digging
into central WA early Saturday east into the Northern
Intermountain West by late Saturday. Confidence in timing Saturday
is moderate-high owning the ensemble forecasts. Clustering
scenarios Friday and Saturday show much of the disagreement
revolves around amplitude/strength with this feature with
phase/timing a secondary driver of uncertainty. This aspect
becomes more lopsided by Saturday with percent variance/fraction
of disagreement in EOF2 that revolving around timing/position is
less than 20% while the percent variance is near 60% in EOF1
associated with the upper trough’s amplitude. Thus high confidence
in the upper trough impacting the region. Of which, the primary
scenario calls the aforementioned trough, albeit one flavor being
strong and the other moderate with all clusters and grand
ensembles showing at least -150 m height anomalies in their 500
hPa forecasts. Of note, one scenario is the upper ridge persist
Saturday but the likelihood is less than 10% with only 7 members
total. 

The primary differences between the strong and moderate trough is
how much beneficial, measurable rainfall will be seen across the
area. The EPS ensemble system is most favorable with its mean IVT
near/above 400 kg/m s showing stout moisture (90th percentile
relative to m-climo) being transported into the interior.
Meantime, GEFS IVT isn’t as bullish and near 250 kg/ m s. The belt
of moisture curves somewhat cyclonically w-e into southern WA and
northern OR beginning late Friday to early Saturday. IVT
probabilities with both systems greater than 250 kg/ m s show 
this moisture is quick in nature and roughly normal to the Cascade
and parallel to the Gorge. A very modest signal in EPS EFI QPF 
with the northern Blues and parts of the Cascades exceeding 0.5. 
Of which, the latter has probs of exceeding 0.5” above 30%. As the
system drops southeastward with its positive PV anomaly Friday 
night, there will be increasing winds with this system with its 
cold front expected to advance through early Saturday. Current 
thinking is gusts up to at least 35 mph are more likely then not.
Highest gusts across north central OR, Blues/Foothills south 
into central OR and the central OR mountains. Fair agreement in 
timing of winds with what is expected to be a gusty period Saturday.
That said, concern is the potential for higher gusts with 
potential of up to 45 mph over the eastern Columbia Gorge, north 
central OR, Foothills, and across parts of south central WA. There
is also concern that there could be downsloping winds as well on
Saturday along the OR cascades (west of Bend/Redmond) given the 
cross-barrier flow setup with strong subsidence and lower static 
stability in deterministic forecasts that will need to be
monitored. As this system advances, pattern generally remains 
unsettled with chances for precip extending through Sunday. 
Meantime, temperatures this weekend are expected to be near 
seasonable to reading slightly below normal by few degrees outside
the Basin and south central WA. 

.AVIATION...06Z TAFs...VFR conditions to prevail through the
period. Clear skies will continue as stable and dry conditions
persist across the region. Terrain and diurnally driven winds will
also continue to be light, less than 10kts, through the
period...except at site RDM where north winds of 10kts to 15kts 
may be possible through this afternoon. Lawhorn/82 


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  40  73  41  73 /   0   0   0   0 
ALW  43  74  44  74 /   0   0   0   0 
PSC  42  74  43  74 /   0   0   0   0 
YKM  41  76  39  77 /   0   0   0   0 
HRI  41  75  41  76 /   0   0   0   0 
ELN  38  76  38  76 /   0   0   0   0 
RDM  31  75  30  76 /   0   0   0   0 
LGD  36  77  36  76 /   0   0   0   0 
GCD  41  81  40  81 /   0   0   0   0 
DLS  46  79  45  80 /   0   0   0   0 

&&

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

$$

SHORT TERM...99
LONG TERM....80
AVIATION...82