784
FXUS66 KPDT 220506
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1006 PM PDT Fri Jun 21 2024

.Updated for Aviation...

.AVIATION...
06Z TAFS...VFR conditions expected for the next few days.
Winds will be 10 kts or less overnight and through the morning
hours on Saturday. However around 22/21Z winds should increase at
DLS/RDM/BDN and become gusty to around 25 kts as a cold front
begins to cross the region. Winds will increase to around 10 kts
or slightly higher at the other sites as well and will likely
increase further beyond the end of the TAF period.

&&

.PREV DISCUSSION... /issued 409 PM PDT Fri Jun 21 2024/

Updated for Aviation...

AVIATION...
00Z TAFS...VFR conditions are expected through the TAF period.
Winds of 10 kts or less can be expected at all sites through
tonight and much of the day on Saturday. However, as a cold front
approaches later Saturday, winds will increase at DLS, RDM and BDN
towards the end of the TAF period and could gust as high as 25
kts. Winds could also pick up at PDT as well. Expect further
increases beyond the end of the TAF period.

PREV DISCUSSION... /issued 221 PM PDT Fri Jun 21 2024/

SHORT TERM...Tonight through Sunday...A dry westerly flow
developing over the PacNW this afternoon has produced light
winds, dry conditions, and hot temperatures. Meanwhile, satellite
imagery is showing scattered cumulus clouds attempting to develop
over the WA Cascades and higher peaks in the eastern mountains.

Today and tomorrow, a thermal trough building in from the south
will continue to bring a warming trend across the forecast area.
Temperatures today are expected to be anywhere from 4 to 10
degrees warmer than yesterday, and another 2 to 5 degrees warmer
on Saturday. While temperatures in the lower elevations Saturday
will be in the 90s, the NBM does show a 20-35% chance that areas
around Hermiston and the Tri-Cities could hit 100 degrees. With
temperatures this warm, HeatRisk values are also increasing into
the moderate category, with widespread moderate in the lower
elevations today and Saturday.

Beginning late tomorrow, a dry upper low with a surface cold front
will approach the PacNW from the the Gulf of Alaska. This system
will begin to tighten the cross Cascade pressure gradient Saturday
evening, resulting in breezy winds developing through the Cascade
gaps during the late afternoon and evening. By Sunday, the upper
low will be swinging into southern BC while dragging the cold
front across the PacNW. The main concern with this system passage
will be the increased winds through the Cascade gaps into the
Columbia Basin, where winds will be 15-25 mph with gusts mainly up
to 40mph. That said, NBM probabilities of 24 hour max wind gusts
greater than 45mph are 60-80% in the Kittitas valley, Simcoe
Highlands, and the OR Columbia Basin. The increased winds will
also coincide with critically low relative humidities across the
Columbia Basin Sunday, resulting in elevated fire weather
conditions. In the Cascade gaps, however, the cooler temperatures
associated with the marine push/frontal passage will keep relative
humidities above critical thresholds. Otherwise, there will be
very little precipitation associated with this system, which will
be mostly confined to the central WA Cascades. In this area,
probabilities for only 0.01 inches of precipitation are only
40%-60%, highlighting the dryness of this system. Alluded to
earlier, the cold front and upper low passage will help break down
the surface thermal trough and bring relatively cooler
temperatures back to the region, albeit afternoon temperatures
will still be in the 80s. The best chances of reaching 90 degrees
on Sunday will be around the Tri-Cities area, where the chance is
only 20-30%. Lawhorn/82

LONG TERM...Monday through Friday...A zonal pattern remains over
PacNW Monday before building into a ridge through Wednesday.
Then, a trough will move inland PacNW late Wednesday into Thursday
until exiting east when another ridge arrives off OR coast
Friday. Models and ensembles are in great agreement with the
weather pattern through Wednesday. However, there are some
differences with Thursday`s pattern and the timing of Friday`s
trough. 21% total members favor a zonal pattern whereas the
majority agree with troughing for Thursday. And Friday, both GFS
and ECMWF show the ridge occurring sooner than Canadian.
Nonetheless, no major weather impacts will happen during the
extended period due to dry conditions.

Confidence remains low for mountain showers at the crest of WA/OR
Cascades and the Blues late Wednesday through Thursday (<30%). The
trough and cold front passage will have limited moisture. Seasonable
temperatures will be Monday with the zonal pattern over the region.
Tuesday into late Wednesday, temperatures warm up again from the
transient ridge but decreases Thursday into Friday with the arrival
of the upper trough off the coast.

Wednesday afternoon will begin with wind gusts at 25-35 mph through
early night along the lower Columbia Basin, Columbia River and
Kittitas Valley (>70% chance). Confidence increases for increased
wind gusts in these areas Thursday from the arrival of the trough.
Breezy conditions will continue across the forecast area with wind
gusts at around 30 mph or less through this remaining extended
period (40-50% probability). Feaster/97

AVIATION...Previous Discussion...18Z TAFS...VFR continues for
this TAF period with current light winds and clear skies. Periodic
mid to high clouds will impact sites during the next 24 hours.
Feaster/97

FIRE WEATHER...A Fire Weather Watch has been issued from Sunday
1pm to 8 pm for wind and low relative humidity for fire weather
zones OR641 and WA691. An incoming dry cold front will result in
breezy to gusty conditions developing in the Lower Columbia Basin,
which will coincide with afternoon relative humidities in the
teens. Strong winds through the Cascade gaps will also produce
elevated fire weather concerns, but relative humidities are
expected to remain above critical thresholds. Current confidence
in elevated fire weather conditions Sunday is 60-70%. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  93  59  82 /   0   0   0   0
ALW  59  96  64  86 /   0   0   0   0
PSC  60  98  64  88 /   0   0   0   0
YKM  61  95  56  83 /   0   0   0   0
HRI  59  98  64  86 /   0   0   0   0
ELN  58  92  57  74 /   0   0   0   0
RDM  53  91  51  82 /   0   0   0   0
LGD  53  91  56  84 /   0   0   0   0
GCD  54  95  55  88 /   0   0   0   0
DLS  63  93  61  78 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Sunday afternoon through Sunday evening
     for ORZ641.

WA...Fire Weather Watch from Sunday afternoon through Sunday evening
     for WAZ691.

&&

$$

SHORT TERM...82
LONG TERM....97
AVIATION...77