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131
FXUS66 KPDT 271143 AAA
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
442 AM PDT Mon May 27 2024

Updated aviation discussion

.SHORT TERM...
Today through Wednesday night...
An upper ridge will be located over the Pacific Northwest early
today. This ridge will move eastward later in the day, allowing
for southwesterly flow to establish itself ahead of an approaching
trough and cold front.

The trough and associated cold front will move onshore Tuesday
afternoon and cross the region through Tuesday night.

There could be lingering precipitation over the mountains into
Wednesday afternoon, then dry conditions Wednesday night. However
it will be cooler on Wednesday.

In the developing southwesterly flow this afternoon/evening, CAPE
will increase to over potentially over 1000 J/KG in spots,
especially across the Blue Mountains and LI values will be in the
range of -1 to -4 degrees Celsius. However, moisture is quite
lacking. During the evening hours, there is at least some better
moisture. So it looks as if there could be some isolated
thunderstorm potential during the afternoon and evening hours, but
overall potential is low (<20%). The Storm Prediction Center has
placed a large portion of central and northeast Oregon and
southeast Washington in general thunderstorms today, though any
activity looks to be later in the afternoon into the evening. The
ECMWF EFI is not all that excited about thunderstorm potential
today.

The better chance of showers in the mountains and thunderstorms is
on Tuesday in increasing southwesterly flow ahead of the advancing
trough. The Storm Prediction Center has placed much of Wallowa
County and a very small portion of Union County in Marginal Risk
of severe thunderstorms, with general thunderstorms expected west
of this area from about Walla Walla to Pendleton, including Grant
County and points eastward.

CAPE values on Tuesday will range from 200 to over 1000 J/kg with
LI values -1 to around -6 degrees Celsius. The highest values will
be further east. As the cold front works its way eastward,
conditions will stabilize, and based on current timing it appears
that any thunderstorm activity should be winding down by early
evening, with CAPE decreasing and LI values becoming positive
behind the passage of the cold front. The ECMWF EFI does key in on
thunderstorm potential on Tuesday mainly across the Blue Mountains
and Wallowas on Tuesday, with a large area of 0.6 to 0.7 for CAPE
and some embedded areas of 0.7 to 0.8.

The other concern on Tuesday will be wind with the front/trough.
It does look to be breezy, especially in the Oregon Basin,
Columbia Gorge, Simcoe Highlands, Kittitas Valley. NBM
probabilities of wind gusts >=39 mph are 80 to 90%. However, NBM
wind gust probabilities of wind gusts >= 47 mph drop to 40% or
less everywhere except in the Kittitas Valley, where they are
about 50%. If a wind advisory is needed anywhere, the most likely
location would be the Kittitas Valley. The ECMWF EFI ranges from
0.5 to 0.7 across the Columbia Basin on Tuesday. On Wednesday
(which would mainly be Wednesday morning), it has values of 0.6 to
0.7 across the Simcoe Highlands and 0.7 to 0.8 across the Kittitas
Valley and 0.6 to 0.8 across the Blue Mountains and portions of
Wallowa County.

High temperatures will be about 5 to 10 degrees above normal today
and will generally be in the upper 70s to lower 80s. Highs will
be cooler on Tuesday and close to normal, with values ranging from
the low 70s to lower 80s. Wednesday, will be even cooler, with
high temperatures ranging from the mid 60s to the lower 70s. These
temperatures are 5 to 10 degrees below normal.

.LONG TERM...
Thursday through Monday...Models start out in good agreement in
having a trough moving off to the east with a ridge building over
area from the eastern Pacific. On Friday, model clusters show
general agreement in having the ridge building further with the
ridge axis just off the coast. The trough moves further east in 80
percent of the model ensemble members while the remaining 19
percent keep the trough over Idaho and still having an influence
over Wallowa County. By Saturday, models develop greater
differences though each case keeps dry weather over our area. 48
percent have a flat ridge centered offshore or just at the coast
with a westerly flow over head and the other 52 percent have the
ridge (with varying amplitude) centered over the Rockies and a
shallow trough just off the coast. On Sunday, 63 percent have a
ridge centered over the Rockies with a southwest flow over our
area, 23 percent have a ridge centered along the coast and 14
percent have the ridge centered several hundred miles offshore
with a weak trough centered along the Idaho border. On Monday,
models favor a strong ridge with significant differences as to the
location of the ridge axis. 38 percent have the ridge axis at the
coast while the other 62 percent have the ridge centered over the
Rockies with a trough approaching the coast. However, the ECMWF
and Canadian deterministic runs have a trough near the coast with
a front moving through the area Sunday night into Monday. The
extreme Forecast Index indicates little in the way of unusual
weather aside from cool temperatures Thursday into Friday with
values of around -0.75.

The result of all this favors mainly dry weather Thursday through
Sunday aside from a slight chance of rain showers along the Cascades
and in the higher terrain of Wallowa County at times. There will
also be a warming trend. Thursday will have a slight chance of light
rain showers from the departing front over the Wallowa mountains and
the higher terrain near Hells Canyon. Winds will be generally light,
though the Kittitas Valley will have northwest winds around 20 mph
in the afternoon. The Columbia Basin will have highs in the upper
60s to mid 70s with mid 50s to mid 60s elsewhere. Lows Thursday
night will be in the upper 30s to mid 40s in the Columbia Basin and
in the lower to mid 30s elsewhere.

Friday and Saturday will remain dry with mainly light winds.
Temperatures Friday will warm to the 70s in the lower elevations
with upper 50s and 60s in the mountains. Saturday will rise to the
upper 70s to mid 80s with upper 60s and 70s in the mountains.

On Sunday, the NBM brings a chance of rain showers to the Cascades
and a slight chance to the eastern mountains in the late afternoon
and Sunday night reflecting the ECMWF and Canadian deterministic
runs. The ECMWF brings in the cold front with the bulk of the
precipitation on Monday, so have a chance of rain in the mountains
and a slight chance in the lower elevations. Temperatures Sunday
rise a couple of degrees from Saturday. Monday begins to show some
cooling with temperatures dropping back to near Saturday`s values.
Overnight low temperatures will show a similar warm up Friday night
through Sunday night, ending up in the mid 50s to lower 60s in the
Columbia Basin and in the mid 40s to lower 50s elsewhere. Perry/83

&&

.AVIATION...
-- Changed Discussion --
12Z TAFs...VFR conditions are expected for the next 24 hours. Under
high pressure today, expect mainly FEW-SCT cirrus at 250 this
morning. This afternoon increasing clouds will develop at 8-12k feet
AGL as high pressure departs and instability increases under a
southwest flow. There will be a slight chance of showers and
thunderstorms over the eastern Oregon mountains after 00Z and could
possibly impact KPDT, KALW and KPSC after 04Z, though the limited
nature of the threat at those sites (<20 percent) kept just a
mention of VCSH in those TAFs. CIGs after 04Z will become BKN-OVC at
8-10k feet AGL. Winds will remain below 12 kts for the next 24 hours
though KDLS, KRDM and KBDN could have a few higher gusts from 21Z-
05Z. Perry/83
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  78  53  74  44 /   0  20  20  10
ALW  81  56  78  49 /   0  20  20  30
PSC  82  58  82  51 /   0  10   0   0
YKM  80  50  77  41 /   0   0   0   0
HRI  82  56  78  48 /   0  10  10   0
ELN  76  52  71  43 /   0   0  10   0
RDM  78  46  69  40 /  10  10  10   0
LGD  78  50  75  44 /  10  10  40  60
GCD  81  49  77  43 /  10  20  60  40
DLS  79  55  70  49 /   0   0   0  10

&&

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

$$

SHORT TERM...77
LONG TERM....83
AVIATION...83