575
FXUS66 KPDT 252117
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
217 PM PDT Wed Sep 25 2024

.SHORT TERM...Today through Friday...

Bottom Line Up Front

...WIND ADVISORY AND DUST ADVISORY IN AFFECT UNTIL 11 PM Wednesday...

1. Windy and Breezy with blowing dust concerns remain through the
   evening.

2. Thunderstorms along the WA Cascades this afternoon and along the
   Blues through Wallowa this evening.

3. Rain along the WA Cascades today and again Thursday evening before
   a return to quite weather.

Short term models are in agreement showing the leading edge of the
front nudging just west of the Cascades. Ground observations are
already showing wind gusts up to 35 mph along the Cascade crests,
33 mph in the Dalles and 36 mph through the John Day Basin. The
front is still just west of the Cascades as seen on the radar.
Ground observations are also showing the precipitation beginning
to move over the Cascades.

Primary concerns for today still revolve around the winds ahead of
this strong cold front. Models show the front to be over the region
beginning in the next few hours which will bring the enhanced winds
with it. Raw ensembles show there to be between 50-70% agreement
that sustained winds through the Gorge, Simcoe, Columbia Basin and
Kittitas Valley will be between 25-30 mph with gusts to 40-45 mph.
Elsewhere, 50-70% of the raw ensembles are showing winds between 15-
25 mph with gust to 30 mph. Winds will remain elevated across those
areas through the later evening. Not only will there be winds, but
due to the time of year and the climate we know and love, these
winds will pick up dust along the way. Blowing dust will make
travel through those areas difficult, dropping visibility to
between one-quarter mile to a mile. If driving in these
conditions, drive with extreme caution.

CAMs show that ahead and a bit behind the front, MUCAPE values
will steadily increase. Model soundings are showing MUCAPE values
along the WA Cascades to be between 300-500 J/kg with LIs of - 1
to -3 and bulk shear of nearing 57 kts. These ingredients could
allow the potential for thunderstorms to develop along the WA
Cascades through the afternoon and evening with 15-20% chances. As
the front moves across the area, CAMs show the Blue Mountains and
Wallowas starting to the MUCAPEs over 500 J/kg, LIs of -2 to
-4, and bulk shear of 40 kts. Again, cannot rule out the potential
for thunderstorms over those areas later this afternoon and
evening with 10-15% chances.

Lastly, this front will also bring with it high mountain rain. As
mentioned earlier, radar is showing the leading edge over the WA
Cascades and putting in a few showers along the western slopes. Raw
ensembles over a 6 hour period are showing 60-80% chances the crests
of the Cascades could see up to 0.15 inches of rain. As the front
moves across the Blues, 40-60% of the raw ensembles show they could
see up to 0.05 inches of rain tonight. Models also show a bit of a
trail of rain making its way through the Cascades again Thursday
evening into Friday early morning with 40-50% of the raw ensembles
showing the WA Cascade crests seeing an additional 0.05-0.10 inches
of rain. After that, Friday will return to dry conditions with zonal
flow aloft. Bennese/90

.LONG TERM...Saturday through Wednesday...Southwesterly flow will prevail on
Saturday, with the flow becoming more westerly by Sunday.  A ridge
will build over the Pacific Northwest from the south for much of the
first half of next week.

As a result, dry weather is expected through at least Tuesday and
possibly longer.  By later Tuesday, guidance begins to diverge with
respect to precipitation chances, at least over the Washington
Cascades.  Much of the area will still be dry.  However, there could
be at least some rain chances over the Cascades later Tuesday into
early Wednesday.

The ECMWF breaks down the ridge faster in the Tuesday/Wednesday
timeframe and develops a trough by Wednesday.  The ensemble clusters
are not supportive of the ECMWF troughier solution, with only about
20 percent of the ensemble clusters supporting that solution.  The
drier ridge or more zonal solution seems to be the preferred
solution, but we are 6 to 7 days out.  Additionally, the GFS
ensemble mean is more supportive of its deterministic run in this
time frame at 500 mb than the ECMWF, which also adds more
credibility to its solution as well.

There will be diurnal breezes, especially Sunday and Tuesday, with
winds expected to gust in the 25 to 30 mph range in the normally
breezier locations.  NBM probabilities of wind gusts >=39 mph on
Sunday are generally in the 50 to 60 percent range.

High temperatures will be 7 to 10 degrees above normal, generally in
the 70s to lower 80s.  The ECMWF EFI focuses in on these
temperatures especially over the eastern half of Oregon with values
of 0.6 to 0.7 and even a small area of 0.7 to 0.8. However, by
Sunday, high temperatures return close to normal for most of the
rest of the extended period.  Monday and Tuesday mornings will be
cool, with lows in the 30s and 40s.  Monday will be the colder of
the two.  Lows could end up about 5 or so degrees below normal but
and depending on how cold it gets, may need to look at freeze
headlines in a few spots.


&&

.AVIATION...18Z TAFS...A strong cold front will move across the area
from west to east this afternoon into early evening.  Winds will
increase and become quite gusty along and ahead of the front with
gusts generally in the 25 to 30 kt range. By early early evening
winds should begin to subside to around 10 kts and become less
than 10 kts by Thursday morning. With the gusty winds, it is
possibly for some BLDU, especially in the Columbia Basin, which
would most likely impact DLS and PSC, but could affect anywhere.
If BLDU does occur, it would bring reduced VSBYS to MVFR, and
possibly lower. The timing and extent is difficult to pinpoint.
For now, have added some reduced VSBYS at PSC and excluded it
elsewhere.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  46  73  48  78 /  60   0   0   0
ALW  49  75  53  80 /  60   0   0   0
PSC  51  75  56  81 /  50   0   0   0
YKM  40  72  46  78 /  20   0   0   0
HRI  49  75  52  80 /  50   0   0   0
ELN  42  71  49  74 /  20   0  10   0
RDM  43  76  43  79 /  30   0   0   0
LGD  46  75  47  80 /  60   0   0   0
GCD  47  78  48  83 /  40   0   0   0
DLS  48  76  55  80 /  50   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 11 PM PDT this evening for ORZ041-507-508-
     510.

     Blowing Dust Advisory until 11 PM PDT this evening for ORZ044.

WA...Wind Advisory until 11 PM PDT this evening for WAZ024-026-027-
     029-521.

     Blowing Dust Advisory until 11 PM PDT this evening for WAZ028.

&&

$$

SHORT TERM...90
LONG TERM....77
AVIATION...77