285
FXUS66 KPDT 260517
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1017 PM PDT Wed Sep 25 2024

Updated Aviation Discussion

.EVENING UPDATE...An eventful evening as areas of blowing dust
were able to encroach into the foothills of the Blue Mountains
here at the office, and we even saw strong winds cause
visibilities below 1/4 mile in the Grande Ronde Valley. But with
the main shield of precipitation now mostly exited out of the
area, winds have dropped significantly and almost all sites are
reporting full visibility again. With this, have discontinued wind
and blowing dust products for the evening. Also made adjustments
to the winds to account for the lowered post-frontal speeds/gusts,
and made some adjustments to precipitation in response to ongoing
activity and how it is expected to evolve this evening.
Goatley/87

.AVIATION...06Z TAFS...VFR conditions to prevail through the
period. Winds significantly weakened across much of the region as
the precip shield moved east of the region. However, winds are
starting to increase slightly this evening at most sites,
generally to around 12-15kts. This trend will continue through
7-10Z, with winds expected to be below 12kts through the rest of
the period. Otherwise, bkn-ovc CIGs AOA 5kft to 12kft AGL will
impact sites through tonight, with clearing skies and a few
passing cirrus decks AOA 15kft AGL developing. Lawhorn/82

PREV DISCUSSION... /issued 451 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.


&&

.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...None.
WA...None.
&&

$$

EVENING UPDATE...87
SHORT TERM...90
LONG TERM....77
AVIATION...82