229
FXUS66 KPDT 170505
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1005 PM PDT Sun Jun 16 2024

Updated Aviation Discussion

.AVIATION...06z TAFs...Light shower activity will continue into
the overnight hours, mainly for RDM, BDN, and PDT. Showers remain
spotty in nature, but have briefly produced MVFR conditions in
central Oregon. By around 10z, rain is expected to dissipate,
with the last of the breezy winds dying down, before picking up
once again by mid-morning Monday. Another round of light showers
is possible Monday afternoon for primarily PDT and ALW, however
the bulk of the rain threat is expected to remain over the eastern
mountains. Cigs will undergo some slight clearing overnight for
sites outside of central Oregon, before building back up again
around the mid-levels tomorrow. Evans/74

&&

.PREV DISCUSSION... /issued 629 PM PDT Sun Jun 16 2024/

EVENING UPDATE...Latest radar imagery this evening shows
scattered showers across the east slopes of the Cascades,
extending from Kittitas County down into central Oregon. A few of
these shower cells have spawned lightning, primarily over the high
terrain in Klickitat and eastern Kittitas Counties, with very
little CG. As we head further into the evening, the thunderstorm
threat will diminish, leaving us with primarily showers, the
threat spreading eastward as the broad trough enveloping the
region shifts eastward. Gusty winds will back down as well, only
to pick up once again tomorrow as the center of low pressure
associated with this trough remains overhead.

Updated the forecast to mention isolated thunder chances in the
aforementioned areas, and updated PoPs based on latest trends.
Also warmed overnight lows a tad, as cloud cover should prevent
temps from dropping below freezing as they did in many elevated
valleys last night. Evans/74

PREV DISCUSSION... /issued 227 PM PDT Sun Jun 16 2024/

SHORT TERM...Tonight through Tuesday...

Key Points:

1) Chance of showers and thunderstorms for our mountains, along
with high elevation snow.

2) Breezy conditions expected again on Monday.

3) Cool temperatures continue through Tuesday before notable
warming trend thereafter.

Showers are beginning to form along the east slopes of the
Cascades as the second in a series low pressure systems impacts
our region. This low will sweep eastward and exit by Tuesday,
bringing the continued chances of precipitation along with further
cool temperatures and some breezy winds. For the precipitation -
the aforementioned showers will continue to increase in coverage
along the east slopes of the Cascades and into the Ochoco-John Day
Highlands through this evening. Some modest instability is
currently present along the Cascades, generally around 100-250
J/kg of CAPE, and models indicate we may reach up to around 500
J/kg, allowing for some strikes of lightning to be possible with
this activity, but support is lacking for any sort of stronger
activity. Into the mountains, this precipitation will also produce
some snowfall, with snow levels at around 4500-5000 feet. With a
lack of significant QPF, these amounts also remain on the lower
side, with a few inches expected outside of the highest peaks.

As the low continues its movement eastwards tomorrow, the pressure
gradient tightens one more time for another round of breezy winds.
Overall gusts are not expected as strong as they were on Sunday,
with the NBM showing a 60-95% chance of gusts 39+ mph for our
normal windy locations (Kittitas Valley, Simcoe Highlands,
Columbia Basin, and Foothills of the Blues). If anywhere were to
gust high enough to warrant a wind advisory (45+ mph), the
Kittitas Valley would be the most likely location.

Finally temperatures remain on the cool side, with highs still 5
to 10 degrees below normal Monday (60`s to mid 70`s for our
population centers), increasing to around 2 to 8 degrees below
normal for Tuesday (widespread 70`s). Overnight lows tonight and
Monday night still show widespread 40`s to 30`s. Some areas of
frost for Central Oregon up through the Wallowas are likely, but
there is low confidence (30%) that we will see further freezes.
The Wallowa Valley is once again the most likely location for a
freeze overnight tonight, but the NBM shows much less widespread
freeze probabilities outside of the mountains leading to the
lower confidence. Lows Tuesday night rise enough that freeze
potential diminishes (widespread 40`s), a signal that our cool
streak is over and summer is on its way back. Goatley/87

LONG TERM...Wednesday through Sunday...Models are in fairly good
agreement through the week but begin to have some timing issues next
weekend.

The Pacific Northwest will be under the influence of a weak and
decaying upper level trough Wednesday into Thursday. The trough will
dissipate allowing the flow to become westerly Friday and then
amplify into an upper level ridge centered over the northern Rockies
on Saturday as the next upper level trough approaches the coast. The
arrival of this trough into the region is the timing issues as the
GFS is slightly quicker than the ECMWF. As of now there is no
convection showers in the forecast as probabilities are below 10%.
However, as the flow aloft becomes more southwesterly late in the
week due to the building ridge this could become an issue over the
eastern mountains as probabilities begin to increase to 10-15%.

Wednesday through Saturday will see a gradual warming trend with
generally light winds. Hottest temperatures of the week will be
Friday into Saturday with Saturday being the peak day. The
probability of temperatures greater than 90 degrees these 2 days
across the Lower Columbia Basin is 50-80% but the probability of
greater than 100 degrees is less than 10%. So, primarily expecting
high temperatures Friday and SAturday across the Lower Columbia
Basin in the lower to mid 90s and 80s in the higher elevations.

Main forecast concern comes over the weekend as the upper level
trough approaches the coast. Past model runs were indicating a weak
marine push possible late Saturday. Current runs are pushing this
back making it more likely to occur overnight and into Sunday. This
will usher in cooler temperatures on Sunday with temperatures
lowering 5-10 degrees. Will see increasing westerly winds becoming
15 to 25 mph along the east slopes of the Cascades spilling out into
the Columbia Basin which could pose an increased risked of fire
spread in existing or new fire starts.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  45  67  43  73 /  30  30  10   0
ALW  47  70  47  76 /  20  50  20  10
PSC  49  75  48  78 /  10  20  10   0
YKM  45  72  43  76 /  30  10   0   0
HRI  49  73  47  78 /  20  20  10   0
ELN  46  67  46  75 /  30  10   0   0
RDM  38  61  33  72 /  40   0   0   0
LGD  40  60  39  69 /  70  80  20  10
GCD  38  59  36  70 /  80  60  10  10
DLS  50  68  48  78 /  20  10   0   0

&&

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

$$

SHORT TERM...74
LONG TERM....91
AVIATION...74