841
FXUS66 KPDT 141126 AAB
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
426 AM PDT Fri Jun 14 2024

Updated Aviation Discussion

.SHORT TERM...Today through Sunday...A cooling trend is in store
the next several days--nothing dramatic--but temperatures will
fall to near to below seasonal averages today and Saturday and
about 10 degrees below average on Sunday. Saturday night will be a
particularly chilly night as radiational cooling allows overnight
temperatures to fall into the mid 20s to mid 30s over the
mountains and mid 30s to mid 40s in the lower elevations. It will
be mostly dry today, and precipitation will develop from the
Cascades westward tonight then increase over the eastern
mountains on Saturday. Drier conditions are forecast to return on
Sunday. The main weather concern for the short term period will be
the gusty winds. A Wind Advisory is in effect for the Kittitas
Valley through 11 AM this morning. Although no additional wind
highlights are expected, gusty winds will always pose problem for
fire spread in dry grassy areas this time of the year.

Overall confidence in the short term is high, although there is
some uncertainty with just how cool we will get on Sunday. The
PacNW will be under a large low pressure trough and cyclonic flow
aloft for the next several days. Westerly winds aloft and at the
surface have increased, and breezy winds gusting to 25-30 mph have
been observed. Ellensburg has observed gusts between 53-57 mph.
There are no plans to upgrade the Kittitas Valley to a warning as
pressure gradients along the WA Cascades are weakening. The
difference between SMP-ELN was 7 mb and now 4.4 mb. Models,
including the HREF, show winds gradually decreasing during the day
and the NBM probability of gusts greater than 48 kts in the
Kittitas Valley is only 20%.

Gradients relax tonight but tight enough to maintain breezy winds.
Clouds will increase tonight ahead of a shortwave trough, and the
trough will bring a 60-80% chance of rain (snow above 4500-5000
feet) along the Cascades and a 30-40% chance of rain (snow above
6000 feet) over the northeast mountains on Saturday. The fairly
strong westerly flow aloft will provide rain shadowing off the
Cascades so that any precipitation that falls in the Columbia
Basin and the Columbia Deschutes Plateau (10-20% chance) will be
minimal. Skies will clear Saturday night and winds will diminish,
resulting in a chilly night. The probability of freezing
temperatures in the lower elevations is low but frost is likely in
the Grande Ronde Valley, John Day Basin, and near Bend/Redmond
where confidence is 60-80% that temperatures will fall into the
mid 30s.

Although all the models advertise the trough over the PacNW on
Sunday for unseasonably cool conditions, the amplitude of the
trough as well as the position of the polar jet are different.
Since the majority of the ensembles keep our forecast area on the
north side of the jet, the thoughts remain that Sunday will be
around 10 degrees below seasonal average.  Wister/85

.LONG TERM...Monday through Friday...There continues to be some
uncertainty in the forecast for Monday into Tuesday with big
differences between the very wet deterministic GFS and dry ECMWF.
This is due to a much deeper closed low in the GFS compared to a
more open wave in the ECMWF. The ensemble clusters favor a more open
wave solution. Also looking at the raw ensemble data it appears that
a drier scenario is more likely to occur (70% confidence) though
there will still be some rain over the eastern mountains and
foothills Monday into Tuesday. Stuck with the NBM POPS for this
forecast which are close to what you would expect based upon the the
ensembles but they could still be a little on the low side (30-55%
POPS).

The 30 GFS ensemble members are much drier overall tonight compared
to last night which suggests that the operational GFS is an outlier
and not likely to happen (5-10% chance of 1.0 inch QPF in the
foothills and around 2.0 inches in the Northern Blues). Utilized
WPC QPF for this forecast which renders .2-.3 inches QPF for the
foothills and and .5-.6 inches QPF for the Blues and Wallowas. This
is close to what the wetter clusters are showing.

On Monday afternoon and evening it is forecast to be breezy to
locally windy in the Cascade gaps with the NBM 24 hour probabilities
of wind gusts exceeding 40 mph at 30-50% in the typically windy
spots under westerly flow regimes. On Monday and Tuesday afternoon
the NBM probabilities of TSTMS exceeded 15% (slight chance) for
portions of the eastern mountains but very difficult to find much
CAPE in the GFS planar fields or forecast soundings. Thus have opted
to keep TSTMS out of the forecast for now.

It will be quite cool on Monday with high temperatures around 15
degrees below normal. Although there are some differences among the
ensemble clusters for the rest of the week, for the most part they
all suggest deamplifying flow and decreasing chances for showers.
This will result in a warming trend. By Wednesday high temperatures
will be about normal for this time of year with slightly above
normal temperatures expected for Thursday and Friday. 78

&&

.AVIATION...12Z TAFs...VFR conditions will prevail through
the forecast period. SCT-BKN clouds at 15-25 kft are expected. Winds
will be mostly 15G25 kt for today into the early evening with a slow
drop off after 04-06Z. 78

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  74  49  66  40 /   0  10  10   0
ALW  77  52  69  44 /   0  10  20   0
PSC  80  55  72  45 /   0   0  10   0
YKM  77  46  69  38 /   0   0  10   0
HRI  79  52  71  44 /   0   0  10   0
ELN  72  46  64  40 /   0   0  10   0
RDM  72  41  61  34 /   0   0   0   0
LGD  72  46  61  36 /   0  10  20   0
GCD  75  43  64  36 /   0   0  10   0
DLS  73  52  66  46 /   0  10  20   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory until 11 AM PDT this morning for WAZ026.

&&

$$

SHORT TERM...85
LONG TERM....78
AVIATION...78