750
FXUS66 KPDT 150925
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
225 AM PDT Sat Jun 15 2024

.SHORT TERM...Today through Monday night...Although no highlights
will be issued for the morning package, there are a few weather
concerns in the short term. Today will be breezy with isolated to
scattered showers and thunderstorms with best probability for
lightning (30%) along the WA Cascades. Showers will end tonight,
clouds and winds will decrease, and it will be a chilly Sunday
morning. The cooling trend continues into Sunday with a 60% chance
of showers along the WA and northern OR Cascades. Showers on
Monday will mainly occur along the Blue Mountains and Wallowas
where PoPs are 40-60%.

The PacNW will be under a longwave upper level trough through
Monday night. A 120kt polar jet is along the base of the trough
with the axis of the jet just south of the WA/OR border. Lapse
rates will be steep over eastern WA today where H5 temps will fall
to around -28C and mid-level lapse rates will increase to around
7-8 C/km. CAPES will range from 150-200 J/kg. Along the WA Cascade
north of Mt. Adams, HREF-calibrated thunder is around 50-60% but
probabilities decrease significantly south and east of Mt. Adams.
There are no organized fronts or shortwaves enhancing showers,
just a westerly flow and orographic lift with channeled vorticity.
Therefore, confidence is high that any precipitation amounts
greater than 0.25" will be along the Cascade crest while the
northern Blue Mtns and Wallowas will receive less than 0.10".
Strong winds aloft and a tight MSLP gradient will keep breezy
winds for most of the forecast area where gusts of 25-35
mph...locally 45 mph...will be a minor nuisance for outdoor
events. Dry grassy areas will be susceptible to fire spread.

Surface winds will gradually decouple from winds aloft and
diminish tonight. Drier air will spread across the region, and
skies will be partly cloudy to mostly clear. Overnight lows will
fall into the 30s to mid 40s...locally in the mid 20s in the
colder valleys such as Ukiah, Seneca, and Sunriver. Confidence
that the Redmond and Bend areas will fall below freezing is around
30-40%, so it will be close. Rather than issue a Freeze Warning
for the central Oregon zone (OR511), will give heads up on social
media and weather graphics that it will be cold tonight with areas
of frost.

Models continue to back off on the QPF for Monday. There are some
model differences on the position of an approaching closed low,
but they all are in agreement that a closed low will dive south-
southeast from the coast to eastern Oregon Sunday night and Monday
with the position of the low near the OR/ID border. Wallowa County
will have the best chance for measurable rainfall. The GFS
continues to have the highest QPF compared to the other
deterministic models, showing 0.15-0.2" in Wallowa County. Wrap-
around moisture often is underestimated in these patterns, so this
cannot be ruled out. However, the GFS has backed off considerably
on the QPF compared to the previous runs. The NBM also has 20%
probability for greater than 0.25", so it doesn`t look to be a
big precipitation producer that models advertised several days ago.
A slight chance (20%) of thunderstorms is forecast for the
northeast mountains associated with steep lapse rates from the
cold upper low. Wister/85


.LONG TERM...Tuesday through Saturday...Ensemble clusters are in
very good agreement on the 500 mb pattern Tuesday through Friday
which will be characterized by a broad trough over the West but with
a gradual deamplification of the flow. On Saturday the clusters show
some differences in the position of the trough axis but this will
have little impact on the sensible weather.

For Tuesday the closed upper low that will be impacting the region
on Sunday and Monday will be moving quickly across MT into s-cntrl
Canada. There may be just enough lingering moisture for a 15-20%
chance of showers over Wallowa County during the afternoon. The NBM
probability of TSTMS in this area is 10-15% with highest values over
eastern Wallowa County. CAPE values are only forecast to be 100-200
J/kg so any TSTMS will be rather brief/weak.

From Tuesday night onward the probability of precipitation will be
less than 10% except for occasional 15-20% chances for light showers
along the immediate WA Cascade crest. High temperatures on Tuesday
will be within a few degrees of normal but a warming trend will
begin Wednesday through Saturday with high temperatures as much as
10 degrees above normal Friday and Saturday. The ensemble clusters
and NBM are depicting lower 90s for highs in the Columbia Basin on
Friday spreading to the Yakima Valley and northern foothills of the
Oregon and SE Washington on Saturday. The ECMWF ensemble is
forecasting 100 degrees for KPSC for Saturday but that seems a bit
warm given the 500 mb pattern. With temperatures climbing into the
90s the NWS experimental HeatRisk is forecast to climb into the
moderate category which means the expected temperatures can affect
those sensitive to heat.

Winds will not be a major concern until possibly Saturday when there
could be a weak marine push during the afternoon/evening . The ECMWF
ensemble members are showing breezy winds for KELN and the NBM is
forecasting sustained winds of 20 mph with gusts to 30 mph at KELN
00Z Sunday. Probabilistic NBM is showing the potential for a little
stronger winds Saturday with a 30-50% chance of 45 mph gusts in the
Simcoe Highlands, Kittitas Valley and portions of n-cntrl ORE. 78

&&

.AVIATION...06Z TAFS...VFR conditions will prevail through the
forecast period. Primary concerns will continue to be the winds
across all TAF sites. BDN/YKM are the only TAF sites that are below
10kts at the moment, but winds are expected to increase there
between 14-16Z. All remaining sites are seeing westerly winds
between 12-15 kts and gusts to 20 mph increasing to 15+ kts and
gusts to 30 kts later in the period. Bennese/90


&&



.PRELIMINARY POINT TEMPS/POPS...
PDT  66  40  66  43 /  10   0   0  20
ALW  69  44  69  45 /  30   0   0  20
PSC  72  45  72  48 /  10   0   0  20
YKM  69  37  69  42 /  10   0  10  10
HRI  71  44  72  46 /  10   0   0  20
ELN  64  40  65  43 /  10   0  10  10
RDM  61  33  62  36 /  10   0   0  10
LGD  61  36  62  39 /  20   0  10  30
GCD  64  36  64  38 /  10   0   0  30
DLS  66  46  69  49 /  20   0   0  10

&&

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

$$

SHORT TERM...85
LONG TERM....76
AVIATION...90