935
FXUS66 KPDT 241714
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1014 AM PDT Tue Sep 24 2024

.UPDATED AVIATION...18Z TAFs...VFR conditions will prevail over
the next 24 hour period. Cigs will begin to move overhead later in
the period with high clouds 25kft and higher. Winds will be
primarily from the south and southwest under 10 kts. Bennese/90


&&


PREV DISCUSSION... /issued 247 AM PDT Tue Sep 24 2024/

SHORT TERM...Today through Thursday night...Today will be warm
and dry with light winds. Strong high pressure aloft and an
inverted surface thermal trough will allow afternoon temperatures
to climb into the 80s to lower 90s--about 15 degrees above
seasonal average. A few record highs may be reached as well. The
air mass is stable with strong low and mid-level inversions,
therefore some of the colder valleys will be slow to reach their
max temperature today and would actually be warmer if not for the
strong inversions in place. It will be another quiet night
tonight, although the upper level ridge will shift eastward and
allow the upper flow to increase from the southwest. Bands of mid
and high level clouds will also move across the area tonight.

Weather concerns ramp up on Wednesday associated with a fairly
organized cold front. Winds and blowing dust will be the two main
concerns with the front. Models push the cold front east of the
Cascades in the afternoon with the ETA along the Cascade Range
between 1200-1400 PDT, across the Columbia Basin down to the
southern Blue Mtns between 1400-1600 PDT, then the rest of the
forecast area between 1600-1800 PDT. There is strong isentropic
descent advertised by the deterministic models that could push
winds aloft to the surface. There is an 850mb jet of 35-40kts and
700mb winds will be as strong as 50kts. ECMWF EFI has a large
area of the Lower Columbia Basin down to Central Oregon in the
0.8-0.9 out of 1.0 for strong winds. The Columbia Basin and
surrounding valleys are often susceptible to blowing dust around
newly plowed fields in late September. Upon further review,
highlights may be needed for winds and blowing dust. Confidence is
high (80%) that patchy blowing dust will be observed but only 30%
confidence that visibilities will fall below 1 mile for a large
area. Will address the blowing dust concern in social media and
weather graphics. Fire season is still upon us, and the hot dry
windy product places some areas in the 90th to 95th percentile.
RHs are not expected to be critically low to meet red flag
criteria, but the Fire Danger Rating Areas are in the moderate to
high category, so fire spread potential remains.

Isolated thunderstorms are also forecast for northeast Oregon and
southeast Washington Wednesday evening. The atmosphere will
quickly destabilize ahead of the cold front, and a few storms are
expected. CAMS gives about a 20% chance of thunder over the Blue
Mountains and Wallowas. Storms that develop have a good chance of
wetting rain but the probability of heavy rain is low (20%).

Thursday and Thursday night will be met with a dry westerly
flow. Seasonal average temperatures will return, and winds will be
locally breezy. Any precipitation will be late Thursday night
(40-60% chance) along the east slopes of the WA Cascades north of
Mt. Adams ahead of a cold front over NW WA. Wister/85

LONG TERM...Friday through Tuesday...A zonal pattern will make its
way over the PacNW through Saturday. Slight chance (20-30%) of
showers occurring at the WA Cascades Friday morning, but could
increase due to orographic lifting from the arrival of the cold
front. Elsewhere will be low (<15% chance). Winds will be fairly
light with occasional breezes up to 20 mph with increased westerly
flow (30-40% probability).

A transient trough will then continue passing through the PacNW
Sunday before an upper ridge builds over starting Monday. Winds
remain fairly light with lingering breezes around 20 mph or less
(>40% probability). Though, models remain deviated for Sunday
where the GFS and Canadian model both favor a shortwave trough
passing through, but with the ECMWF being zonal.

Tuesday, the ridge will break down as another shortwave trough
arrives with a cold front inland of the forecast area. With
orographic lifting and southwest flow, chances of evening showers
could increase. But, confidence is low (20%). The GFS and Canadian
models show the trough moving over to the forecast area whereas
ECMWF favors a ridge. If the trough occurs, cooler temps and
potential showers will continue. But if not, then a upper ridge
builds over off the OR coast thus returning warm temps and dry
conditions. Being said, this can make it challenging to forecast
given the uncertainty. High temperatures will be mainly in the 70s
through the long term period. Feaster/97

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  88  58  82  47 /   0   0  20  40
ALW  91  64  87  50 /   0   0  20  50
PSC  88  62  87  51 /   0   0  20  30
YKM  88  55  81  40 /   0   0  30  20
HRI  91  60  84  49 /   0   0  20  30
ELN  88  56  78  43 /   0   0  50  20
RDM  91  54  81  40 /   0   0  10  20
LGD  86  58  87  47 /   0   0  20  50
GCD  87  54  86  47 /   0   0  20  20
DLS  93  59  79  50 /   0   0  40  20

&&

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

$$

SHORT TERM...85
LONG TERM....97
AVIATION...90