659
FXUS66 KPDT 202128
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
228 PM PDT Sat Jul 20 2024

.SHORT TERM...Tonight through Monday...Upper level ridging over
the western CONUS will continue to amplify into Canada today,
while a shortwave trough offshore CA will approach southwestern OR
this evening. Temperatures will continue to warm today as a
result of the amplifying ridge and an inverted thermal trough at
the surface. The NBM shows probabilities of 80-95% exceeding or
meeting 100 degrees this afternoon in the Columbia Basin, Gorge,
and Yakima valley, with probabilities 50-70% in other heat prone
areas.

The ridge will continue to amplify into Canada Sunday while the
shortwave trough will split as it moves north along the PacNW
shore, with the bottom portion of the shortwave moving inland
Sunday afternoon and exiting early Monday morning. The upper ridge
will continue to influence temperatures across the region Sunday,
with another 3 to 6 degrees of warming across the Columbia Basin
and adjacent valleys. Along the OR Cascade gaps, a weak marine
push associated with the incoming shortwave trough passage will
result in temperatures mainly in the mid to upper 90s, with
probabilities of reaching 100 degrees less than 25% in central OR
and the Gorge. Elsewhere in the lower elevations, probabilities of
reaching 100 degrees are 85-95%, with a 35-50% chance of reaching
110 in portions of the Basin near Hermiston and the Tri-Cities.
The shortwave trough passage throughout Sunday will also introduce
isolated to widely scattered thunderstorm chances across the
Cascades and central OR, capable of producing gusty outflows and
abundant lightning (confidence 65-85%). The shower and isolated
thunderstorm potential will move north along the Cascade east
slopes through Sunday evening, before diminishing Sunday night.

By Monday, an upper low in the Gulf of Alaska will push the upper
ridge east with the low gradually pushing inland through the
remainder of the week. Temperatures will begin to cool across the
area, albeit by only 2 to 5 degrees into the 90s and lower 100s in
the lower elevations Monday afternoon. Though confidence is very
low (10-15%), an isolated thunderstorm threat will remain over
the Blues in the afternoon thanks to linger upper level
instability over the forecast area. Otherwise, the last concern
for Monday will be increasing winds through the Cascade gaps and
into the Columbia Basin. Winds of 15-25mph with gusts up to 40mph
are expected through the Gorge, far western Columbia Basin, and
the Kittitas valley with winds 10-20mph and gusts up to 30mph
across the remainder of the lower elevations. While winds will
increase across these areas, RHs will also be on the increase as
cooler temperatures filter into the region. While critical wind/RH
fire weather conditions are not expected, elevated fire weather
concerns remain, especially if increased winds impact area fires.
Lawhorn/82

.LONG TERM...Tuesday through Saturday...

Key Messages:

1. Much cooler than in recent days becoming near normal Thursday
through Saturday.

2. Little if any chance of showers or thunderstorms with a 10-15
percent over the highest eastern Oregon mountains on Wednesday.

3. Breezy afternoon winds through the Cascade gaps each day,
strongest on Thursday and Friday.


Models are in excellent agreement through the long term period in
having a trough affecting the area with only a few minor differences
developing late in the week that should have little impact on the
forecast. Overall, temperatures will be cooler, especially Thursday
through Saturday. The Extreme Forecast Index highlights well above
normal temperatures in the eastern mountains Tuesday through
Thursday with values of 0.85 to 0.95, while other areas are not
highlighted. Otherwise, no abnormal weather is indicated.

On Tuesday, a strong upper low will be centered off the northern
British Columbia coast with a trough axis centered a few hundred
miles off the Pacific Northwest coast. A ridge will be centered over
the Rockies with a southwest flow over our area. Instability
parameters look vary stable so do not anticipate any showers or
thunderstorms. Pressure gradients look tight along the Cascades, the
Kittitas Valley and the Eastern Columbia Gorge and those areas will
have northwest winds of 10 to 20 mph in the afternoon. Temperatures
will be a degree or two cooler than Monday with highs in the lower
to mid 90s in the lower elevations including the John Day and Grande
Ronde Valleys and in the 80s in the mountains. The Tri-Cities and
Hermiston will have about a 25 percent chance of 100 degree
temperatures and John Day about a 50 percent while all other
locations will have less than 15 percent chance.

On Wednesday, the upper low moves to the British Columbia coast and
the trough axis moves a little closer to the coast. Circulation
around the trough helps strengthen the ridge to our east and this
raises 500 MB heights over our area, which warms our temperatures a
couple of degrees. This gives us highs in the mid 90s to around 102
in the lower elevations and in the 80s to lower 90s in the
mountains. There will be a 25 to 50 percent chance of 100 degree
temperatures in the lower elevations. Pressure gradients are
slightly tighter and winds through the Cascade gaps will reach 15 to
mph in the afternoon. Models indicate a 10-15 percent chance of
showers or thunderstorms over the Elkhorn, Strawberry and Wallowa
mountains but with those low values, kept the dry forecast of the
NBM for now.

On Thursday, the trough moves overhead and the ridge moves further
off to the east. The cooler air with the trough drops temperatures
7 to 10 degrees to the upper 80s to lower 90s with mid 70s to mid
80s in the mountains. Probabilities of 90 degree temperatures in the
lower elevations are 40 to 70 percent. Winds will again reach 15 to
25 mph in the afternoon.

On Friday, the lower low weakens and begins ejecting northeast into
northern Saskatchewan and Alberta though a shallower trough remains
overhead. Temperatures are a degree or two cooler than Thursday and
the 90 degree probabilities drop to 25-50 percent. Pressure
gradients weaken a bit and winds through the Cascade gaps in the
afternoon are 10 to 20 mph. The chance for showers and thunderstorms
continue to look minimal.

On Saturday, the trough weakens further and is more shallow. Models
have a more westerly flow aloft. Temperatures warm a degree or two
to the upper 80s to lower 90s with mid 70s to mid 80s in the
mountains. 90 degree probabilities rise to 70 to 75 percent for the
Tri-Cities and Hermiston and 30 to 60 percent in the rest of the
lower elevations. Winds are a couple mph lighter than Friday.
Perry/83


&&

.AVIATION...Previous Discussion...18Z TAFs...VFR conditions will
continue for the next 24 hours with primarily clear skies and
light winds. Hazy conditions due to smoke from area wildfires will
continue but is not expected to reduce visibility at local
terminals below 6SM but that could happen locally elsewhere. Late
this evening and overnight, mid level clouds will move into
central Oregon becoming BKN100 with VCSH at KRDM and KBDN after
12Z. Winds will remain below 12 kts except for KDLS having
northwest winds at 14 kts gusting to 20 kts after 15Z tomorrow
morning. Perry/83


&&

.FIRE WEATHER...Hot, dry, and unstable conditions will persist
over fire weather zones OR642 and OR644, resulting in Red Flag
Warnings in effect through Sunday for these areas. Unstable
conditions will continue into Monday, however temperatures will be
cooling and RHs increasing above critical thresholds. Isolated to
widely scattered thunderstorms will also be developing across
southern portions of central OR Sunday afternoon, with abundant
lightning and gusty outflows possible. As a result, Red Flag
Warnings are in effect for abundant lightning for fire weather
zones OR611 and OR640. Additionally, there are concerns for
elevated fire threat due to increasing winds late Sunday as the
cooler air associated with an the approaching trough begins to
push into the region. This will produce winds of 10-20 mph with RH
values in the teens to lower 20s. Winds continue and increase on
Monday but RH values will be higher generally in the 20s.
Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  63 104  65  96 /   0   0  10  10
ALW  67 108  69 100 /   0   0   0  10
PSC  66 107  70 100 /   0   0  10   0
YKM  67 105  68 100 /   0   0  10   0
HRI  65 107  68  98 /   0   0  10   0
ELN  63 104  67  94 /   0   0  10  10
RDM  60  96  56  93 /   0  20  20   0
LGD  60 104  63 100 /   0   0   0  10
GCD  64 105  63 102 /   0  10  20  10
DLS  69  95  66  88 /   0  10  20   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning until 10 PM PDT Monday for ORZ041-044-049-
     050-502-503-505-507-508.

     Red Flag Warning until 11 PM PDT Sunday for ORZ642-644.

     Heat Advisory until 8 PM PDT Monday for ORZ506-510-511.

     Red Flag Warning from noon to 10 PM PDT Sunday for ORZ611-640.

WA...Excessive Heat Warning until 10 PM PDT Monday for WAZ024-026>030-
     521.

     Heat Advisory until 8 PM PDT Monday for WAZ523.

&&

$$

SHORT TERM...82
LONG TERM....83
AVIATION...83