000
FXUS66 KPDT 181718
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1018 AM PDT Mon Oct 18 2021

Updated aviation discussion

.UPDATE...Primary edits to the forecast in the short term were
tweaks to temperatures based on morning lows, as well as edits to
skies based on current cloud cover trends. Otherwise, a day of
clearing is anticipated through much of Tuesday as low pressure
sliding over California and Nevada departs or region, allowing for
a brief period of weak ridging. Winds will be the main concerns
for both today and later tomorrow, as breezy westerly flow is
expected today, becoming weak into early Tuesday and then gustier
from the south overnight Tuesday into Wednesday as the next low
approaches our region. Goatley/87

.AVIATION...18z TAFs...VFR conditions expected with just some FEW-
SCT mid level clouds impacting RDM, BDN, PDT and ALW today but then
clear overnight. Breezy 10-20kts at DLS through the afternoon,
otherwise winds less than 10 kts.

&&

.PREV DISCUSSION... /issued 257 AM PDT Mon Oct 18 2021/

SHORT TERM...Today through Wednesday night...A closed low
centered near Lake Tahoe is rotating showers over southern
Oregon, but most precipitation is south of the forecast area.
There will be a few more hours with scattered showers south of
Redmond and John Day before ending as the low moves into NV. By
noon today, showers will end. A WNW pressure gradient will
strengthen, and surface winds 10-20 mph and locally higher gusts
can be expected. Otherwise, it will be a quiet weather day with
highs mainly in the 60s throughout the Columbia Basin and in the
50s elsewhere. It will be a chilly night as skies clear and winds
diminish with lows in the 20s in the mountains and valleys and in
the 30s in the lower elevations.

It will be another quiet and seasonably warm day on Tuesday, but
weather concerns for Tuesday night through Wednesday evening
revolve around the next Pacific frontal system. The biggest
forecast challenge will be winds. It will become windy in several
areas due to a tightening surface pressure gradient and
increasing southerly winds aloft, particularly in the Grande Ronde
Valley, the foothills of the Blue Mountains east-southeast of
Walla Walla and Pendleton as well as near Heppner/Lexington, and
the Long Creek area. Strong winds along the Eagle Caps may cause
downslope winds near Joseph as well. The 4-KM WRF-GFS highlights
these areas for 25-35 mph gusts, and further prognosis of the
high resolution models will give more details as they become
available.

Models have done a good job with the track and strength of the
next Pacific front, as the upper trough takes a negative tilt and
quickly traverses across OR/WA Tuesday night and Wednesday. The
best chance for precipitation in the forecast area will be between
sunrise and noon, and QPF amounts will range from a few hundredths
to 0.2 inch--nothing significant but every zone has at least a
chance of some light precipitation. Snow levels will range from
6000-7000 feet.  Wister/85

LONG TERM...Thursday through Monday...Much of the long term period
is characterized by a wet SW flow pattern that will provide a
persistent chance for showers across much of the CWA. Deterministic
models depict the source of this pattern through a deepening
offshore upper-level low, which ensembles show lifting up along the
BC coast Friday into Saturday. This trajectory would provide the
forecast area with a decent shot of moisture aloft through much of
the period, and the NBM has reflected this with PoPs above 30% for
most of the CWA. Looking at ensemble clustering, solutions have been
smoothed out such as to depict primarily an ongoing SW flow pattern
beyond even the end of the long term, but the overall synoptic
pattern supports what could potentially be a wet weekend.

Emphasis on forecast will be more towards valley rain rather than
any mountain snow, as SW flow aloft will work to keep snow levels
above 5000-6000 ft for most of our elevated zones. Predicting QPFs
this far out will be a challenge, as the synoptic pattern can change
across models substantially this time of year, but ensembles all
pointing towards similar synoptic patterns suggests a decently high
confidence in some kind of precipitation occurring across the CWA
over the next weekend. Towards the end of the period, model
solutions begin to diverge a bit more, but both the deterministic
GFS and ECMWF suggest a more broad low based out of the Gulf of
Alaska that would keep us under a wet pattern beyond even the long
term. Temperatures will be average, with highs in the 50s and 60s,
dropping slightly should the first offshore low lift out of the area
before the more broad system trailing it has time to establish more
SW flow aloft into our area. 74

AVIATION...12z TAFs...VFR conditions expected. An upper-level
system will move out of the forecast area this morning, allowing for
clearing skies through the day Monday. Locally breezy conditions
possible during the afternoon, otherwise mostly W/NW winds less than
15 kts. Sct-bkn cigs around 10-15 kft early, becoming mostly clear
by the evening. 74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  62  35  67  45 /   0   0   0  10
ALW  64  40  67  49 /   0   0   0  10
PSC  68  41  66  47 /   0   0   0  10
YKM  67  35  64  40 /   0   0   0  10
HRI  66  39  68  47 /   0   0   0  10
ELN  63  37  60  41 /   0   0   0  10
RDM  57  30  67  41 /  20   0   0  30
LGD  59  34  65  47 /   0   0   0   0
GCD  59  33  66  45 /  20   0   0  10
DLS  63  41  68  49 /  10   0   0  30

&&

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

$$

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

NWS PDT Office Area Forecast Discussion