481
FXUS66 KPDT 251736
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1036 AM PDT Sat May 25 2024

.AVIATION...18z TAFs...VFR conditions through the TAF period with
dry conditions. The main impacts at area terminals will be gusty
to breezy wind through the evening. The strongest wind is expected
at KDLS and KPDT, where gusts of 30 to 35 kt are favored (85-90%
chance). Most other terminals will see the potential for gusts to
25 kts (70-90% chance). Wind will weaken between 03z and 10z
Sunday with winds generally below 12 kts expected through the
remainder of the TAF period.

&&

.PREV DISCUSSION... /issued 926 AM PDT Sat May 25 2024/

MORNING UPDATE...The main update this morning was to increase
forecast wind speeds and gusts for the Kittitas Valley through
tonight. At the synoptic level, northwesterly flow through the
much of the column will persist over the PacNW as an upper-level
trough axis exits to the east over the Rockies through the day.
Moreover, morning soundings at SLE/UIL show the top of an upstream
marine layer around 850 to 750 mb. Cross-Cascade surface pressure
gradients range from 4-5 mb from SEA to ELN and are advertised by
CAMs to be maintained through the evening. While NBM and HREF
probabilities are marginally supportive of advisory criteria,
pattern recognition increases forecaster confidence. Thus, have
issued a Wind Advisory through 11 PM this evening as confidence is
high (70-80% chance) that marginal advisory criteria (sustained
winds of 25-35 mph with gusts of 35-45 mph) will be maintained
through the day. Plunkett/86

PREV DISCUSSION... /issued 458 AM PDT Sat May 25 2024/

SHORT TERM...Today through Monday night...An upper trough over
the Pacific Northwest will move eastward during the day today.
Some generally light showers, mainly over the mountains will occur
early before drying commences as dry northwesterly flow moves in
over the entire region.

Dry weather is then expected for the remainder of the short term
period, with the exception of the Washington Cascades, where there
could be a few showers on Sunday.

The flow will become more westerly on Sunday then southwesterly
Sunday night. By Monday night, there could be a few showers,
mainly over the Blue Mountains. However, for the vast majority of
the area, the holiday weekend looks dry, with warming temperatures
each day.

With the trough over the Pacific Northwest today, there will be
some breezy conditions, mainly over the Oregon Columbia Basin,
Simcoe Highlands and Kittitas Valley. Winds should gust in the 25
to 35 mph range, with locally higher gusts to 40 mph possible. The
NBM probabilities of winds >= 39 mph in these locations are
70-100%. However, the wind gust probabilities of >= 47 mph are
generally 40% or less. The ECMWF EFI also keys in on wind gusts
across much of this area, with values mainly in the 0.6 to 0.7
range.

High temperatures today will be 5 to 10 degrees below normal, with
readings mainly from the low 60s to possibly the lower 70s in the
Columbia Basin. Highs on Sunday will be much warmer and much
closer to normal and generally in the low to mid 70s everywhere.
On Memorial Day, highs will be warmer still, and will be 5 to 10
degrees above normal, ranging from the upper 70s to lower 80s.

LONG TERM...Tuesday through Saturday...Models start out in good
agreement in having a ridge over the Rockies and a closed low and
trough off the west coast. A cold front will come ashore in the
afternoon and evening followed by a second weaker front Wednesday.
Models are diverging by Thursday with 71 percent of model ensemble
members having a trough somewhere over the Pacific Northwest
while the remaining 29 percent have a flat westerly flow over the
area. Differences grow on Friday as model ensemble members are
fairly equally divided between having a ridge overhead, a trough
overhead or a ridge offshore with a shallow trough over northern
Montana and southern Saskatchewan. Friday shows a similar widely
varied set of solutions though there is a preference of a ridge
somewhere over the region with only 20 percent of model ensemble
members favoring a trough over our area. Fortunately, the Extreme
Forecast Index shows few concerns in the long term period. It does
highlight convective energy for thunderstorms over the eastern
Oregon mountains on Tuesday with a 0.70 value. It also highlights
below normal high temperatures on Wednesday and Thursday and below
normal low temperatures Thursday morning and Friday morning with
values of -0.67 to -0.75 mainly over the mountains. Overall
forecast confidence is good on Tuesday and then declines, becoming
below normal by Friday and Saturday.

On Tuesday, the cold front will bring a chance of showers to the
mountains and the Blue Mountain Foothills along with a chance of
thunderstorms in the eastern mountains in the afternoon and
evening before tapering off overnight. The eastern mountains
will get as much as a third of an inch of rain while other areas
with precipitation will have just a few hundredths of an inch.
Winds will pick up with the frontal passage and westerly winds of
15 to 25 mph are anticipated in the afternoon and early evening.
The front will affect temperatures in central Oregon the most with
temperatures dropping 6 to 8 degrees to the lower 70s while the
rest of the area will cool 2 to 4 degrees to the mid 70s to lower
80s. Low temperatures Wednesday morning will cool 4 to 8 degrees
to the mid 40s to lower 50s in the Columbia Basin and in the upper
30s to mid 40s elsewhere.

On Wednesday, models favor the trough moving ashore with a
weakening closed low over British Columbia and then crossing the
area though Wednesday night. The mountains will have a chance of
afternoon showers with just minor amounts of rain. A slight chance
of thunderstorms will be confined to the higher terrain near John
Day. The afternoon will have a recurrence of westerly afternoon
winds though a little slower at 10 to 20 mph. With the low
overhead, temperatures will cool further to the 60s with a few
lower 70s in the Columbia Basin.

Thursday becomes more uncertain, but the GFS and ECMWF
deterministic runs both have the departing low and trough over
western Montana with moisture circulating into the eastern
mountains and further west, an upslope flow into the Cascades.
Have kept a chance of showers and a slight chance of thunderstorms
over the eastern mountains and a slight chance of showers
elsewhere except dry in the Columbia Basin. Rain amounts will be
up to a tenth of an inch in the mountains and light elsewhere.
Temperatures will be a degree or two cooler than Wednesday.

Uncertainty continues on Friday and Saturday though the model
deterministic runs favor a ridge crossing the area, so have a
slight chance of very light mountain rain showers Friday and
Saturday. Temperatures begin recovering to the mid 60s to mid 70s
Friday and then to the 70s on Saturday. Perry/83

AVIATION...12Z TAFs...VFR conditions will continue for the next
24 hours. Skies will be SCT-BKN at 040-080 through 03Z then rise
to SCT-BKN at 090- 150 through 12Z tomorrow morning. Mountain rain
showers will end by 20Z this afternoon. At KDLS and KPDT, west to
northwest winds at 10- 20 kts with gusts to 25-30 kts will
increase to 20-25 kts with gusts to 35 kts then start decreasing
after 04Z and dropping below 12 kts after 08Z. KPSC and KALW will
become southwest at 10-20 kts with gusts to 30 kts from 15Z
through 05Z after which KPSC will drop below 12 kts while KALW
will shift to the south and continue at 10- 15 kts with gusts to
20 kts. KRDM, KBDN and KYKM will have northwest winds at 10-20 kts
with gusts to 30 kts from 20Z-04Z then drop below 12 kts. Perry/83

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  62  40  71  46 /  10   0   0   0
ALW  66  44  73  49 /  10   0   0   0
PSC  71  46  76  51 /   0   0   0   0
YKM  68  40  73  44 /   0   0   0   0
HRI  67  44  76  49 /   0   0   0   0
ELN  62  43  68  44 /  10   0  10   0
RDM  59  33  72  41 /  10   0   0   0
LGD  59  36  69  42 /  20   0   0   0
GCD  59  35  71  43 /  20   0   0   0
DLS  64  46  74  49 /  10   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory until 11 PM PDT this evening for WAZ026.

&&

$$

MORNING UPDATE...86
SHORT TERM...77
LONG TERM....83
AVIATION...76