656
FXUS66 KPDT 202119
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
219 PM PDT Fri Sep 20 2024

.SHORT TERM...Today through Sunday night...

Key Messages:

1. Breezy winds this evening, returning Sunday.

2. Warming trend through weekend, reaching above normal Sunday.

Current radar and visible satellite imagery showing dry conditions
under clear to mostly clear skies extending across the region.
This is in response to an upper level ridge pushing onshore and
into the Pacific Northwest in the wake of a weak shortwave along
the Canadian border and another slow, upper low pressure system
moving east through Southern California. These synoptic features
have allowed a weak pressure gradient to develop along the
Cascades, providing breezy west northwest winds across the Gorge,
Kittitas Valley, and portions of the Basin. Winds of 25-35 mph
have been observed at these locations this afternoon, and will
begin to dissipate after 9 PM. Confidence in wind gusts of 30 mph
or greater is high (80%) over the Kittitas Valley, as the HREF
suggests a 70-90% chance of this occurring. The chance of 35 mph
wind gusts is considerably lower to between a 10-30% chance. Winds
through the Gorge are also expected to be on the lower end of the
25-35 mph range this evening, as the HREF advertises a 30-50%
chance of gusts reaching 30 mph or greater, and dropping to a 10%
when bumping up gusts to 35 mph. Today`s northwest flow turns
more from the west Saturday before a return to northwest flow on
Sunday associated with a weak shortwave. This feature on Sunday
will attribute to a chance (15-35%) of showers along the Central
Washington Cascades and another surface pressure gradient
developing along the Cascades. Elevated winds are expected to
return to the Kittitas Valley and the Gorge, with gusts of 25-35
mph out of the west northwest and peaking between 2 PM and 6 PM.
Confidence in these gusts is moderate (70%) as the NBM suggests a
60-80% chance of gusts of 30 mph or greater over the
aforementioned areas Sunday.

Elevated winds both today and Sunday are not expected to result in
any fire weather concerns, as the afternoon humidities will be
improving slightly through the weekend. However, overnight
recoveries will be on the decline through Saturday night ahead of
excellent recoveries returning Sunday night associated with the
incoming shortwave. Temperatures will also be on the increase
through Sunday, with above normal high temperatures anticipated
and highs breaking into the low 80s for lower elevations of the
Basin. Confidence in 80 degree high temperatures on Sunday is
moderate (60%) as the NBM showcases a 50-80% chance of Sunday`s
highs reaching 80 degrees or above for Yakima (78%), Tri-Cities
(51%), and Hermiston (51%). 75


.LONG TERM...Monday through Friday...

Bottom Line Up Front

1. Dry and warming conditions through mid-week

2. Diurnal winds through the Cascade Gaps

3. Cascade rain and a cooling trend late next week

Models are in firm agreement with the upper level ridge moving
overhead at the start of the forecast period. Dry and warmer
conditions will prevail under the ridge through Wednesday before an
upper level trough breaks it down bringing rain to the crests and
east slopes of the Cascades as well as diurnally driven enhanced
winds across the wind prone areas in the CWA.

Even with the upper level ridge moving overhead, EFI is signaling at
or near normal seasonal temperatures through Wednesday. Monday the
majority of the CWA will see temperatures in the mid to upper 70s
with 80-100% of the raw ensembles in agreement. However, 40-60% of
the raw ensembles have the Basin and the Gorge in the low 80s. As
the ridge settles overhead, temperatures will steadily warm with
Wednesday being the warmest day of the period. 70-90% of the raw
ensembles show the majority of the lower elevations and central OR
to be in the low to mid 80s while the higher mid-level terrains will
see upper 70s. Temperature will begin to cool a few degrees as the
upper level trough brings with it cooler temperatures bringing the
majority of the region back into upper 60s to low 70s.

With the current pattern set up under the ridge, winds will remain
the typical diurnally driven winds below 15 mph through the Cascade
Gaps and along the foothills with 80-100% agreement. However, winds
will briefly pick up Wednesday and Thursday as the upper level
trough moves across the region. Models do show a very weak pressure
gradient moving across the Cascades which will bring the heightened
winds. However, only 40-60% of the ensembles show the winds to be at
or near 15 mph both days while 60-90% show the region to primarily
see winds near 10 mph. Thursday ensembles show much of the same
before slightly decreasing Friday.

Models are in some agreement with the incoming upper level trough.
Clusters show the biggest variance between the models is the timing
and precipitation at the onset. EURO brings the trough in much
sooner with lighter amounts of precipitation along the Cascades; GFS
brings it in faster with much more rainfall associated with it and
extending the rain over the Blues. With that said, forecast is using
the NBM which appears to be more on track with the EURO solution of
light rain along the Cascades and the Blues. 20-40% of the raw
ensembles show the WA Cascades seeing 0.02 inches of rain Thursday
while less than 20% show 0.01 inches along the Blues. With that said
and the fact that this is day 7, confidence in the chances of rain
are low (10-20%). Bennese/90


&&

.AVIATION...18Z TAFs...VFR conditions will prevail through
the forecast period. CIGs will be mostly clear skies with some
high clouds moving overhead later in the period. Winds will
continue to remain breezy at DLS through 03Z, PDT through 23Z and
RDM/BDN through 20Z. Bennese/90


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  72  43  77 /   0   0   0   0
ALW  46  74  47  79 /   0   0   0   0
PSC  47  76  49  80 /   0   0   0   0
YKM  43  75  47  81 /   0   0   0   0
HRI  45  76  46  81 /   0   0   0   0
ELN  42  75  46  80 /   0   0   0   0
RDM  35  71  39  78 /   0   0   0   0
LGD  40  71  41  76 /   0   0   0   0
GCD  37  72  40  77 /   0   0   0   0
DLS  47  79  50  83 /   0   0   0   0

&&

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

$$

SHORT TERM...75
LONG TERM....90
AVIATION...90