812 
FXUS66 KPDT 160519
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1019 PM PDT Sat Oct 15 2022

Updated Aviation Discussion

UPDATE...Quiet weather continues tonight as high pressure remains
over the Pacific Northwest. The ridge axis has moved from offshore
last night to the Cascade crest and this may give us slightly 
warmer temperatures tonight than last night. Did make a few minor 
temperature adjustments. Freeze warning for the Grande Ronde 
Valley looks good and will remain through tomorrow morning. High 
mountain locations like Seneca and Sunriver may drop to the upper 
20s as well. Winds are decreasing and moving into typical 
nighttime drainage directions. Made a few minor adjustments to the
wind as well. Clear skies should continue into tomorrow morning. 
Other than the minor temperature and wind adjustments, the 
forecast was in good shape and no additional changes were made. 
Forecast update already out. Perry/83

AVIATION...06Z TAFs...VFR conditions to prevail through the
period. Site PSC has seen reductions in vsby down to 5SM 
overnight and early in the morning the past several days,
however there is low confidence in timing and intensity, so have 
left out mention of vsby reduction. Otherwise, mainly clear skies 
will prevail across all sites. Terrain and diurnally driven winds 
will remain light, less than 10kts, through the period. Lawhorn/82


PREV DISCUSSION... /issued 431 PM PDT Sat Oct 15 2022/ 

SHORT TERM...Tonight through Monday night. Minor sensible weather
concerns that revolve around the threat for sub-freezing
temperatures across the Grande Ronde Valley and limited parts of
central OR. Meantime, highs continue to read above seasonable
normal values by 8-12 degrees with fair weather prevailing and
limited cloud cover, except for smoke/haze near area fires. 
Latest day cloud phase distinction RGB shows some thin cirrus 
moving across parts of south central OR and northeast OR, 
otherwise clear skies overhead. Latest water vapor imagery shows 
a well amplified upper ridge with its center offshore the WA 
coast extending into the Yukon territory with the region under a 
blocking regime. Otherwise, modest offshore flow/easterly winds 
ongoing with thermally induced trough extending over southwest OR.
Northeasterly gusts as high as 25 mph across parts of south 
central WA and north central OR occurring with potential for gusts as
high as 30 mph, especially on ridge tops. 

Current thinking is our high valleys will see similar conditions
as this morning thus good potential (>80%) for sub-freezing
conditions. That said, the freezing threat will extend and exist 
in the Grande Ronde Valley as air dries out with low dew points 
anticipated. This setup with adequate radiational cooling 
conditions via clear skies and light winds late night/early 
morning will promote temperatures as low as 30 F there. High 
confidence in clear/mostly clear skies with HREF handling the 
absence of clouds well and matches our current thinking for 
overnight and tomorrow. As such a freeze warning was issued. While
NBM probs were modest for sub-freezing temperatures, the 
combination of recent observation trends and the setup increased 
our confidence. Meantime, there is spotty potential for 
approaching/around 32 F in central OR, generally near Redmond, 
OR. However, confidence in coverage outside of it being spotty was
low and the freeze threat is anticipated to be limited over 
greater central OR on the whole. Looking ahead, little change in 
highs Sunday and Monday, perhaps a couple degrees cooler Monday, 
as the upper ridge evolves to be more over the Northern 
Intermountain West by Sunday. Light easterly breezes continue 
along with fair conditions. 

LONG TERM...Tuesday through Saturday...Dry and abnormally warm 
conditions continue through the middle of the week however a 
transition to a more active weather pattern appears increasing 
likely next weekend. The extended period begins with an area of 
high pressure still exerting its influence across much of the 
Western US. This stable rex block pattern due to the accompanying 
cut-off low offshore of southern California ensures the 
continuation of dry and relatively calm conditions through 
Thursday, thereby also extending the long streak of above normal 
daytime temperatures. That said, most deterministic and ensemble 
guidance depict the high pressure weakening Wednesday night and 
Thursday but it likely won’t result in any appreciable differences
in conditions until Friday. Both the ECMWF and GEFS ensemble 
means maintain 8 to 13C 850mb temperature anomalies through this 
time period resulting in high temperatures rising into the 70s for
a significant portion of the CWA each afternoon. Climatologically,
these values are roughly 10 degrees above normal for mid-October.
Conversely overnight lows hold a bit closer to normal due to 
clear skies and longer nights supporting efficient radiative 
cooling. Daytime temperatures should begin trending closer to 
normal Friday into the weekend as the pattern begins to progress. 

Both deterministic and ensemble guidance are in fairly good
agreement on the arrival of a troughing feature originating from
the Gulf of Alaska late Friday into Saturday. However, at this 
time there are noteworthy discrepancies regarding the potential 
impacts of this disturbance owing to uncertainty in the timing but
more-so the amplitude of this feature as highlighted by the 
variance in the ensemble cluster analysis EOF patterns. Further 
exploring the cluster analysis reveals a split between ensemble 
systems and their members on how to handle the trough with a large
portion, greater than 80%, of ECMWF members favoring a strong 
feature dropping through the CWA. By comparison, a contingent of 
GEFS and Canadian members either place the trough further east 
and/or don’t show a trough at all(roughly 15% of the total grand 
ensemble members). The former scenario heavily favored by the 
ECMWF and containing the highest percentage of the total grand 
ensemble members(around 65%) would result in much needed wetting 
rain for almost all of the mountain zones into portions of the 
inland PacNW accompanied by windy conditions. Precipitation in the
latter cases would be noticeably limited, if any occurred at all.
If there’s any silver lining models have been slowly trending 
away from the dry solutions. But, even with this in mind, 
confidence in widespread rainfall is still only moderate at this 
time given the uncertainty shown in the GEFS/Canadian ensemble 
systems and in the NBM ensemble. Confidence in QPF values should 
increase in the coming days as we get closer to this event. 
Schuldt/99

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  70  40  76  38 /   0   0   0   0 
ALW  71  45  77  42 /   0   0   0   0 
PSC  78  45  76  42 /   0   0   0   0 
YKM  78  44  76  42 /   0   0   0   0 
HRI  74  43  76  40 /   0   0   0   0 
ELN  75  42  76  38 /   0   0   0   0 
RDM  71  32  79  34 /   0   0   0   0 
LGD  72  38  75  37 /   0   0   0   0 
GCD  77  43  80  40 /   0   0   0   0 
DLS  80  48  80  44 /   0   0   0   0 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Warning from 4 AM to 9 AM PDT Sunday for ORZ049.

WA...None.
&&

$$

UPDATE...83
SHORT TERM...80 
LONG TERM....99 
AVIATION...82