346
FXUS66 KPDT 120321
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
821 PM PDT Tue Jun 11 2024

.UPDATE...
Winds have begun to decrease across the region and have lowered
enough that the wind advisory has been cancelled. Winds will be
breezy for several more hours before finally dropping during the
overnight hours. Otherwise, just made some minor tweaks to
overnight lows.

.AVIATION...
06Z TAFS...VFR conditions expected for the next few days. DLS will
keep 20 to 25 kt gusts for a few hours before winds decrease to
around 10 kts. Winds will increase and become gusty again with 20
to 25 kts in the afternoon before decreasing in the evening.
Similarly PDT will keep gusts for a few hours but will have winds
10 kts or less on Wednesday. All other locations should have 10
kts or less through the period.

&&

.PREV DISCUSSION... /issued 424 PM PDT Tue Jun 11 2024/

Updated for Aviation...

AVIATION...
00Z TAFS...High Confidence (95-100%) in VFR conditions through the
period. Gusty winds this evening will subside in most locations
this evening and everywhere overnight, with winds becoming 10 kts
or less and remaining there. The only exception is DLS which will
have gusty winds 20 to 25 kts again Wednesday afternoon.

PREV DISCUSSION... /issued 258 PM PDT Tue Jun 11 2024/

SHORT TERM...Tonight through Thursday Night...

Key Messages:

1. Breezy to windy conditions through this evening with wind
advisories issued for the Kittitas Valley, Eastern Columbia Gorge
and Simcoe Highlands.

2. Cooler Wednesday but warming back up Thursday.

A weak shortwave is passing to our north through central British
Columbia this afternoon and it has a cold front that will cross our
area a few hours from now. Radar is not showing any shower activity
and satellite shows clouds mainly west of the Cascades with mostly
clear skies over our area. The main concern today is the winds,
which will be peaking later this afternoon and then decreasing this
evening after sundown. The GFS, NAM, SREF and GEFS all have pressure
differences between Portland and Spokane in excess of 10 MB with the
RAP is between 9-10 MB. These values point to windy conditions in
the Columbia Basin and adjacent valleys. Observations have been
mainly in the 20 to 30 mph with gusts to 35-40 mph so far but winds
are increasing. Ellensburg had northwest winds of 31 mph gusting to
46 mph in the latest observations. NBM probabilities show a greater
than 90 percent chance of wind gusts of 40 mph in Kittitas Valley.
Simcoe Highlands, Columbia Gorge and and a 50-90 percent chance in
the Blue Mountain Foothills later this afternoon. Chances for a wind
gust of 49 mph are 70 percent chance in the Kittitas Valley and 50-
60 percent in the Simcoe Highlands and Columbia Gorge but drop off
to less than 15-30 percent elsewhere. Current wind advisories for
the Kittitas Valley, Simcoe Highlands and the Eastern Columbia River
Gorge look good and will remain in effect through 11 PM this
evening. Winds look to remain just below wind advisory levels in the
Columbia Basin, Blue Mountain Foothills and Yakima Valley. Relative
humidities are as low as 20-25 percent as well and a few weeks from
now, would probably need to consider a Red Flag Warning for fire
danger but believe the vegetation is still a bit too green for large
fires.

As winds die down this evening after the cold front passage, colder
air will move over the area and along with clear skies, temperatures
will drop off as much as 8 to 12 degrees from last night with lows
in the 40s in the lower elevations and in the mid 30s to lower 40s
in the mountains. Tomorrow, with the shortwave moving into the
Rockies and the next trough still up in the Gulf of Alaska, a zonal
westerly flow will be over the area and sunny and dry weather is
expected. Winds will be fairly light with only the Kittitas valley
and Columbia River Gorge reaching 10 to 15 mph in the afternoon.
Lingering cooler air will drop temperatures 5 to 8 degrees from
today and highs will be in the mid 70s to lower 80s in the lower
elevations and in the mid 60s to mid 70s in the mountains. Lows
Wednesday night will be a few degrees warmer than tonight but still
a few degrees below normal in most locations.

On Thursday, a strong upper low and trough will begin moving south
out of the Gulf of Alaska to the central british Columbia coast.
This will send a warmer southerly flow over our area. There will
continue to be no chance of precipitation through Thursday night but
there will be increasing cloudiness along the Cascades and in the
northern portion of the area in the afternoon and Thursday night.
Winds will continue to be light through Thursday evening but will
become breezy overnight in the Columbia Basin and adjacent wind
prone valleys. Highs Thursday will rebound back to the lower to mid
80s with 70s and lower 80s in the mountains. Lows Thursday night
will warm to the mid 40s to mid 50s. Perry/83

LONG TERM...Friday to Tuesday...The main sensible weather
highlights include:

- Breezy to locally windy conditions across our windy/climo-prone
areas Friday and Saturday,

- Cooler, below normal temperatures with the coldest conditions this
weekend, particularly Sunday, and

- Unsettled weather this weekend onward with generally periodic
chances, highest along the crest of the Cascades and eastern
mountains.

The long term initially will be characterized by a deep, anomalous
upper-level closed low offshore British Columbia with southwest flow
aloft with the expectation of a weak front moving across Thursday
night. Ensemble guidance is in very good agreement with the synoptic
pattern as cyclonic flow dominates through Saturday with the upper
trough forecast to evolve to the WA/BC region. A modest synoptically
imposed surface pressure gradient will develop late Friday and
persist Saturday with the stronger winds prevailing Saturday.
Limited support aloft in the lower troposphere until more so
Saturday. 24-hr peak daily gusts chances for exceeding 40 kts around
60-95% over the eastern Columbia Gorge into the Lower OR Basin,
Simcoe Highlands, and the Kittitas Breezeway, highest across the
later area. Slightly higher probs, by 10-15%, on Saturday across the
same locations. That said, chances for exceeding 45 mph are around
25-50%, except for 60-90% across the Kittitas Valley. Meantime, the
best chances (50-80%) for precip in the long term will arrive
Saturday across the WA Cascades near the crest.

As the upper trough evolves, an cooler air mass is anticipated to
take hold this weekend. This in tandem with limited sky cover across
some areas will favor radiational cooling when/if combined with
light winds as well. Of which, lows will be around 3 to 10 degrees
below normal area-wide Sunday morning across the lower elevations;
lows will be into the 30s across parts of central OR. Confidence is
low right now in central OR seeing lows below 32 with chances
peaking around 25% across Redmond.

Thereafter there are modest differences in the 500 mb pattern
beginning Sunday that grow more by Monday/Tuesday next week with the
latest guidance in fairer agreement compared to overnight.
Specifically, the amplitude and character of the upper trough early
next week. There is potential for embedded wave(s) to deepen this
upper trough Monday over the Northern Intermountain West, or the
other possible outcome is a pattern that becomes more progressive,
less amplified with open waves/shortwave troughs passing across the
PacNW. Confidence in more persistent upper-level troughing affecting
the region around ~80% and 90% Monday and Tuesday, respectively.
Currently there are low to moderate chances (15-50%) across the
upper slopes of the eastern Cascades and the eastern mountains
Sunday, highest odds in the former. Lower confidence on Monday and
Tuesday with chances more broad and lower overall (15-40%).
Lastly, there are concerns (~15-20%) for isolated thunderstorms
Monday, however, confidence is low giving the spread in guidance
and uncertainty this far out in time.

AVIATION...Previous discussion...18Z TAFS...VFR conditions prevail
during this TAF period. Most sites currently have FEW-SCT clouds
except KRDM with clear skies. Cloud coverage will decrease
throughout the day for KDLS/KPDT/KALW/KPSC. All sites will
experience gusty westerly winds at 20-30kts with sustained winds
at 15-25kts this late morning. These wind conditions should
decrease overnight but afternoon for KDLS (>50% confidence).
Feaster/97

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  47  76  46  83 /   0   0   0   0
ALW  48  79  49  86 /   0   0   0   0
PSC  50  81  50  87 /   0   0   0   0
YKM  44  79  46  84 /   0   0   0   0
HRI  47  81  48  87 /   0   0   0   0
ELN  45  76  46  82 /   0   0   0   0
RDM  40  77  43  83 /   0   0   0   0
LGD  43  74  45  84 /   0   0   0   0
GCD  44  79  46  89 /   0   0   0   0
DLS  50  80  50  85 /   0   0   0   0

&&

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

$$

SHORT TERM...77
LONG TERM....80
AVIATION...77