888
FXUS66 KPDT 222334
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
433 PM PDT Wed May 22 2024

Updated aviation discussion

.SHORT TERM...Today through Friday...

Key Messages:

1. Windy conditions this afternoon and evening.

2. Thunderstorms possible through this evening.

3. Warming conditions Thursday and Friday.

Current visible satellite imagery shows the upper level low
pressure system moving into northeast Oregon as it slowly
transits the area from northwest to southeast through the day
today. This, coupled with a passing cold front, has allowed a
pressure gradient to develop along the Cascades, bringing
elevated winds across the area. Wind gusts between 45-55 mph have
already been observed at the Ellensburg, Pendleton, and Hermiston
airports, with these winds expected to linger into the evening
hours. Thus, a Wind Advisory has been issued for the Lower
Columbia Basin of Oregon and the northern Blue Mountain foothills
until 5 PM; as well as north central Oregon and the Kittitas
Valley until 9 PM this evening. Guidance has had a tough time
capturing the extent and strength of winds today, which lends only
moderate confidence (50-60%) in these elevated wind gusts
lingering through much of the evening.

Current radar imagery is showing several discrete thunderstorm
cells developing across the Lower Columbia Basin and northern Blue
Mountains/foothills as increased cloud-to-ground lightning
strikes have been occurring in the last hour. This activity is
expected to continue through the afternoon and extend south into
the John Day-Ochoco Basin before subsiding shortly after 8 PM.
The highest surface CAPE values (100-200 J/kg) exist from Boardman
east to the northern Blue Mountains, with the higher wind shear
(30-40 knots) further south in the John Day-Ochoco Basin as
advertised by the HREF. These marginal convective conditions lead
to high confidence (80%) that cells will stay discrete and storms
sub-severe. However, there is a chance of pea-sized hail (30-50%)
and a slight chance of a brief cold-core funnel (5-15%). Showers
will linger through the evening across the John Day-Ochoco
Highlands, Elkhorns, and higher elevations of the northern Blue
Mountains before drying into Thursday morning. Another upper
level shortwave will be passing through the Pacific Northwest on
Friday, returning shower chances to our mountain zones (40-60%)
and the foothills (20-35%). A slight chance of thunderstorms also
returns to areas of the northern and southern Blue Mountains
Friday afternoon and evening. Surface CAPE looks marginal between
100-150 J/kg, so discrete cells and sub-severe conditions are
likely (70-80% confidence).

A transient upper level ridge will move into the area in the wake
of the departing upper level on Thursday, providing drier and
warmer conditions with the latter extending into Friday as an
approaching and passing upper level trough will enhance southwest
flow aloft. High temperatures will be bumping up 10-15 degrees on
Thursday and another 5 degrees on Friday as highs reach into the
mid-to upper 70s for lower elevations of the Basin, which is near
normal values for this time of year. 75


.LONG TERM...Saturday through Wednesday...The long term will be
characterized by active weather with a slight reprieve between
systems. An upper level tough will begin the period off ahead of an
upper level ridge followed yet another trough. Temperatures will
begin to hover back towards near normal with near normal
precipitation as well.

Models are in relatively decent agreement with the upper level
trough axis being over the forecast area on Saturday. Clusters show
the main variance between the ensembles to be with the amplitude of
the trough. All solutions however, do suggest there to be some light
precipitation over the mountains with some rain/snow along the
higher peaks with snow levels between 4500-6000ft. 20-40%
probabilities of between 0.01-0.03 inches of rain along the Cascades
and less than 15% along the northern Blues Mountains. Also, NBM
ensembles are showing between 10-15% probability of thunderstorms
along the far eastern mountains of Wallowa County late Saturday
morning into early afternoon. Guidance is picking up on some light
instability over the area and slightly warmer temperatures along the
Snake River. Couple that with the westerly flow and orographic lift,
one can not rule out the probability of a stray thunder clap.
Temperatures over the forecast area will be near normal according to
the EFI guidance with over 48% of the raw ensembles showing the
Pendleton area in the upper 50s to 60s, 41% has the Basin in the
upper 60s to low 70s, 67% having north and central OR in the 50s and
lastly, the higher elevations in the mid 40s. Winds will be breezy
as the trough passes with 60-80% probabilities of the Gorge, Blues,
Columbia Basin and adjacent valleys seeing sustained winds of 25 mph
or greater.
By Saturday evening the models show the upper level tough move
eastward while the system behind the trough flattens the flow to a
zonal flow with westerly winds. With the zonal flow, surface
pressure gradients will loosen allowing a reprieve from the windy
conditions.

Sunday through Tuesday afternoon the models continue to be in decent
agreement with the zonal flow beginning to give way to an upper
level ridge. This will bring dry and warming conditions back to the
area. Clusters remain vigilant with the main variance being with the
amplitude of the incoming ridge. With this shift in pattern, winds
will be mostly light with some diurnal variances through the Gorge,
lower Columbia Basin and adjacent Valleys with 30-50% probabilities
of sustained winds of 20 mph. EFI remains steady with the
temperatures being at or slightly above normal with 45-50% of the
raw ensembles showing the Pendleton area in the low 70s, increasing
to low 80s Monday and Tuesday. 50-60% show the Basin in the mid to
upper 70s Sunday increasing to mid 80s Monday and Tuesday, over 50%
showing norther and central OR in the upper 70s to low 80s and the
higher elevations in the upper 50s increasing to the low 60s Monday
and Tuesday.

Tuesday night through Wednesday the models remain in decent
agreement with the upper level trough begins to push back into the
region bringing with it chances of precipitation and slightly cooler
temperatures. With this upper level low, guidance is beginning to
pick up on some elevated instability over the region with the bulk
showing up primarily over the eastern mountains. NBM ensembles show
a 10-20% 6 hour probability of thunderstorms over the eastern
mountains Tuesday evening. Ensembles show the CAPE values increasing
to over 100 J/kg during the same time frame with 40-60%
probabilities. With this being day 7 and 8, confidence in the
chances of thunderstorms is low/moderate at this time. With the
incoming trough, NBM is showing temperatures to decrease with the
passage as well as an increase in the surface winds nearing 20 mph
through the Cascade Gaps and along the foothills. Bennese/90


&&

.AVIATION...00Z TAFS...An upper level low over the region will
continue to provide showers through the evening mainly impacting
PDT and ALW with showers and possible thunderstorms then ending and
partial clearing overnight. Overall expecting VFR conditions but
could see brief MVFR conditions at PST and ALW through 06Z. Winds
are decreasing but could see some 10-20kts winds with gusts around
30kts through the early evening then becoming less than 10 kts
overnight and Wednesday.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  67  43  68 /  70  10   0  10
ALW  45  69  47  73 /  30  10   0  20
PSC  48  74  49  76 /  30  10   0  10
YKM  43  74  45  74 /  20  10   0  10
HRI  44  73  47  74 /  60  10   0  10
ELN  44  69  43  70 /  10  10   0  10
RDM  33  65  39  65 /  10   0   0  10
LGD  38  61  39  67 /  60  10   0  30
GCD  37  62  38  67 /  80  10   0  30
DLS  47  71  48  71 /  20  10   0  10

&&

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

WA...None.

&&

$$

SHORT TERM...75
LONG TERM....90
AVIATION...97