336
FXUS66 KPDT 230924
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
224 AM PDT Sun Jun 23 2024

.SHORT TERM...Today through Tuesday night...Red flag conditions
and strong winds will be the primary weather concerns today. The
Red Flag Warning in effect for the Lower Columbia Basin of WA/OR
(fire zones WA691 and OR641) will be expanded to include central
Oregon (fire zone OR640) in effect this afternoon and evening. A
wind advisory is in effect for the Kittitas Valley starting at 5
AM this morning through midnight.

Winds have already increased across the Lower Columbia Basin and
surrounding valleys. These winds are providing mixing of warm and
dry air aloft to the surface, resulting in early morning
temperatures in the lower 70s and RHs in the upper 20s and 30s. To
give a feel for how dry it is aloft, the 00Z UIL sounding has a
dewpoint spread of around 26C at 700mb. However, the depth of the
marine layer at UIL is from the surface to 850mb. GOES nighttime
microphysics shows the marine layer banked up along the west side
of the Cascade Range. The marine layer will deepen as the day
progresses with the passage of a shortwave trough and dry cold
front. There will not be significant winds associated with the
front with the exception of the Kittitas Valley where sustained
winds around 30 mph gusting to 45 mph are forecast. Confidence is
high for these winds to be observed, but gusts at 50+ mph have a
much lower probability (0% from the HREF and 30% from the NBM). As
far as fire weather concerns, the marine layer seeping through
the Cascade gaps will keep RHs high enough along the Kittitas
Valley and eastern CR Gorge despite the gusty winds. Deterministic
models are in good agreement with Min RHs around 30% for these
areas. RHs over the Lower Columbia Basin will be in the teens and
20s. Central Oregon will observe RHs in the teens as well with a
few spots in the single digits. Since the winds are forecast to be
a little stronger in central Oregon, a Red Flag Warning will be
issued to include this zone.

Winds aloft and at the surface will decrease tonight, and Monday`s
winds will be considerably less than today. Afternoon highs on
Monday will be about the same or a tad cooler than today and
closer to seasonal average. No weather concerns are anticipated
for Monday night through Tuesday night. However, the westerly flow
will begin to back to the southwest on Tuesday as an upper level
trough develops offshore. Afternoon temperatures will climb back
into the 80s to mid 90s with the HeatRisk in the minor to moderate
category. There are signs of elevated instability over eastern
Oregon as well, but the threat of any thunderstorms is low...less
than 15%. There is limited mid-level moisture but no indications
of an upper level disturbance to provide the lift needed. However,
I would expect cumulus buildups over the Blues and the John Day-
Ochoco Highlands Tuesday afternoon and evening. Wister/85


.LONG TERM...Wednesday through Sunday...Southwest flow expected over
the region as an area of low pressure approaches the PacNW on
Wednesday. Precipitation associated with this system has a slight to
moderate chance (40-60%) of impacting the Cascade Mountains starting
Wednesday. Additionally, temperatures will decrease on Wednesday by
a few degrees, though values will generally still be around 5
degrees above normal. Wind will be the other consideration for
Wednesday. Wind speeds will increase through the afternoon and
evening hours, with the strongest wind favored to be across the
Columbia Basin, Columbia River Gorge, and into the Kittitas Valley.
In these locations, there is a 60-80% chance for winds of 25 mph
with gusts of 30-35 mph on Wednesday afternoon and evening.
Additional areas of Washington and Central Oregon will see 70-90%
chance for winds around 20 mph with gusts near 25 mph for the same
timeframe. Windy conditions will weaken slightly overnight.

The area of low pressure continues to move through the area on
Thursday, though models and clusters show variations in placement
and related strength of the system`s influence on Thursday. The NBM
has a return of gusty to breezy wind on Thursday afternoon, but
keeps any threat of shower activity generally confined to the higher
terrain. There are some solutions (GFS mainly) that do hint at the
potential for showers across the lower elevations, though confidence
in that development remains low. Further cooling temperatures
anticipated Thursday with values landing around 5 degrees below
normal. While wind will see another increase in the afternoon, winds
are not expected to be as strong. The favored locations of the
Columbia River Gorge and the Kittitas Valley remain, with most of
these areas seeing a 70-90% chance for winds around 20 mph with
stronger gusts. The presence of winds stronger than that is more
isolated.

The area of low pressure will generally move east of the forecast
area by Friday, allowing a drier, northwest flow to influence the
region. A warming trend in temperatures returns with values reaching
near normal values on Friday with widespread dry conditions. This
pattern will keep winds generally light. Similar conditions expected
Saturday with additional warming. An approaching wave late Saturday
into Sunday will turn flow southwesterly again, with a few showers
present over the higher terrain. Branham/76

.AVIATION...06Z TAFS...VFR conditions are expected across all TAF
sites. However, the main concern will be wind as a cold front makes
its way across the region. Winds will increase overnight and become
gusty by afternoon at all TAF sites. DLS is already gusting to
around 30 kts. It is possible that they will see some lower winds
overnight before picking back up again. All other sites will
increase to around 25 kts, with most decreasing late in the period
around 24/04Z to around 10 kts or less.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  81  48  81  51 /   0   0   0   0
ALW  85  52  84  54 /   0   0   0   0
PSC  87  52  86  55 /   0   0   0   0
YKM  83  46  83  51 /   0   0   0   0
HRI  85  52  86  55 /   0   0   0   0
ELN  74  47  80  51 /   0   0   0   0
RDM  82  43  83  47 /   0   0   0   0
LGD  83  47  82  51 /   0   0   0   0
GCD  89  47  87  52 /   0   0   0   0
DLS  77  52  83  55 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 1 PM this afternoon to 8 PM PDT this
     evening for ORZ640-641.

WA...Red Flag Warning from 1 PM this afternoon to 8 PM PDT this
     evening for WAZ691.

     Wind Advisory from 5 AM early this morning to midnight PDT
     tonight for WAZ026.

&&

$$

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