771
FXUS66 KPDT 100957
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
257 AM PDT Mon Jun 10 2024

.SHORT TERM...Today through Wednesday...

Key Messages:

1. Breezy winds Tuesday afternoon and evening.

2. Above normal temperatures approach near normal on Wednesday.

Current radar and infrared satellite imagery showing dry
conditions and clear skies, which is a result of an upper level
ridge beginning to build across the region in the wake of the
departing system. This ridge will provide sunny skies across the
area today as high temperatures increase 2 to 5 degrees from
Sunday, reaching into the mid-to upper 80s across lower elevations
of the Basin and along the foothills. Flow aloft will turn from
the northwest through much of the day as the upper level ridge`s
axis slowly moves onshore, leading to breezy winds along the east
slopes of the Cascades, Eastern Gorge, and the Kittitas Valley.
Sustained winds of 15-20 mph and gusts of up to 30 mph are
anticipated to peak 2 PM and 8 PM today, with directions out of
the west across the Gorge and northwest in the Kittitas Valley.
Confidence in these wind values is high (80-90%) as the HREF
suggests a 90% chance of wind gusts reaching 25 mph or greater in
Ellensburg, decreasing to a 10% chance when increased to 30 mph
or greater. The upper level ridge will shift east tonight as an
upper level shortwave flattens it quickly over the Pacific
Northwest on Tuesday. This will allow a dry cold front to quickly
pass the region, allowing a pressure gradient to form along the
Cascades as isobars tighten at upper levels to support breezy
winds across the Gorge, Lower Columbia Basin of Oregon, and the
Kittitas Valley. Sustained winds of 20-30 mph and gusts of 35-43
mph will be possible, with highest values occurring over the
Kittitas Valley. Confidence in these wind values is moderate to
high (60-80%) as the NBM highlights a 70-80% chance of 40 mph wind
gusts or greater across the aforementioned areas, dropping to a
60-70% chance of 47 mph gusts or greater. There is also
consistency in model guidance in regards to the strength of the
pressure gradient building along the Cascades, with the GFS and
NAM both highlighting a gradient of 11-12 mb between Portland and
Spokane (11 mb is the normal advisory threshold). However, wind
speeds have trended downward over the last 24 hours and 850 mb
winds of only 40-45 mph are forecast via the GFS and the ECMWF. At
this time, confidence in wind advisories being issued for Tuesday
is moderate (30-60%), with the highest chance (50-60%) being over
the Kittitas Valley.

As stated above, high temperatures will be warmer today under
sunny skies but will cool through the period. Today`s passing
upper level ridge will allow for northwest flow aloft to initiate,
which will turn more from the west to allow high temperatures to
drop 1 to 3 degrees on Tuesday. A more noticeable drop in
temperatures will occur Tuesday night into Wednesday as flow
aloft becomes more northwest in the wake of the exiting trough and
ahead of the approaching ridge. Clear skies overnight will also
support additional cooling as Wednesday morning temperatures drop
into the upper 40s to low 50s across the lower elevations of the
Basin and the foothills, and into the low to mid-40s through
Central Oregon and the Yakima Valley. High temperatures will drop
another 3 to 7 degrees on Wednesday as afternoon temperatures
only reach into the upper 70s to low 80s across Lower elevations
of the Basin, foothills, Gorge, and Central Oregon, which is near
normal for this time of year. 75


.LONG TERM...Thursday through Monday...There is excellent ensemble
agreement (all four cluster scenarios) that a deep, upper-level
closed low will propagate southeastward towards the Pacific
Northwest from the Gulf of Alaska on Thursday. Flow aloft will turn
southwesterly in response to the approaching system. Coupled with
mostly clear skies, forecast 850-mb temperatures strongly suggest
afternoon high temperatures will be above seasonal averages. NBM
probabilities further corroborate this outcome; the chance of
exceeding 80 degrees is 80-100% for our major population centers,
and the chance of exceeding 90 degrees is 10-20% for the lower
Columbia Basin. HeatRisk concerns are "Minor", or a category 1 on
Thursday. This level of heat primarily affects individuals extremely
sensitive to heat.

Friday through Monday, ensemble concensus loosens regarding the
evolution of the aforementioned low as it tracks into the Pacific
Northwest. However, confidence is high that a cooling trend will
commence Friday with area-wide near- to below-normal temperatures
persisting through Monday. Ensemble cluster scenarios range from an
upper-level closed low overhead to a weaker open-wave trough across
the Washington and southern Canada.

Breezy to windy westerly gap winds on Friday and Saturday will be
the primary instigator of any potential highlights. NBM
probabilities suggest a 30-90% chance (predominantly 30-60% except
for climatologically windy locations) of 24-hr maximum wind gusts
exceeding advisory magnitude (45 mph) for the lower Columbia Basin
of OR, foothills of the northern and southern Blue Mountains of OR,
the eastern Columbia River Gorge of OR/WA, the Simcoe Highlands, and
the Kittitas Valley.

While the low will have the potential to bring rain to the forecast
area Friday through Monday, chances of wetting rain (0.1" or higher)
are low with the exception of the Cascade crest. To illustrate this,
NBM 24-hr probabilities of a wetting rain through the period are the
following: less than 10% for central OR, the Columbia Basin, the
eastern Columbia River Gorge, and the Yakima and Kittitas valleys;
10-15% for the foothills of the Blue Mountains and Blue Mountain
valleys; 15-20% for the Blue Mountains; 15-25% for the OR Cascade
crest; 25-55% for the WA Cascade crest. Plunkett/86


&&

.AVIATION...12Z TAFs...VFR conditions are very likely (>95% chance
for all sites). Diurnally driven winds of 10 kts or less are
forecast for all sites except DLS where westerly gap flow of 15 kts
with gusts to 25 kts is forecast Monday afternoon and evening.
Existing FEW-BKN altocumulus and high-level cirrus (primarily over
the Columbia Basin) will transition to SCT-BKN cirrus through
afternoon and evening. Plunkett/86


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  83  55  83  48 /   0   0   0   0
ALW  85  59  87  52 /   0   0   0   0
PSC  89  59  89  52 /   0   0   0   0
YKM  87  56  84  45 /   0   0   0   0
HRI  88  58  87  51 /   0   0   0   0
ELN  80  54  74  47 /   0   0   0   0
RDM  82  51  82  43 /   0   0   0   0
LGD  79  50  82  46 /   0   0   0   0
GCD  81  53  85  47 /   0   0   0   0
DLS  85  59  79  50 /   0   0   0   0

&&

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

$$

SHORT TERM...75
LONG TERM....86
AVIATION...86