487
FXUS66 KPDT 111615 AAA
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
915 AM PDT Tue Jun 11 2024

.MORNING UPDATE... Current winds in Ellensburg, The Dalles and along
the Blue Mountain Foothills are already at around 20 mph with gusts
of 30 to 35 mph, so the expected windy conditions are developing.
Wind advisories for the Kittitas Valley and Simcoe Highlands look
good and believe the Columbia Basin will remain just below wind
advisory levels. The winds, along with very dry soil moisture values
in Washington and the Oregon Columbia Basin, will make blowing dust
possible today with the higher wind gusts. Have added patchy
blowing dust today and this evening to the Kittitas Valley and
Simcoe Highlands as well as portions of the Columbia Basin and the
Blue Mountain Foothills. Otherwise, the forecast looks good and no
other changes were made. Forecast update already out. Perry/83


.SHORT TERM...Today through Thursday...

Key Messages:

1. Breezy to windy conditions today. *Wind Advisories Issued*

2. Cooling trend through Wednesday.

Current radar and infrared satellite imagery showing dry
conditions as pockets of mid-to high level clouds pass across the
Columbia and John Day-Ochoco Basins. This is a result from the
transient upper level ridge, that brought sunny skies and warm
temperatures across the area Monday, continuing to exit to our
east. An upper level trough is currently approaching Vancouver
Island, and will be passing to our north later today. A dry cold
front will be associated with this system and will transect the
area, allowing a pressure gradient to develop along the Cascades.
This will lead to windy conditions across the Kittitas Valley,
Simcoe Highlands, and the Eastern Gorge, as sustained winds of
20-35 mph and gusts of up to 50 mph are anticipated. Thus, a Wind
Advisory has been issued for the aforementioned areas between 9 AM
and 11 PM today. Confidence is high (80%) in wind gusts reaching
advisory criteria, as the GFS and NAM suggest a pressure gradient of
11.5-13 mb will develop between Portland and Spokane (11 mb is
normal advisory threshold). Further confidence is gleamed from the
NBM, which highlights an 80-95% chance of wind gusts of 45 mph or
greater over the earlier mentioned areas, with the ECMWF EFI showing
60-70% of ensemble members indicating above climatological normal
wind gust values. A significant temperature gradient of 7-10 degrees
will also be setting up along the Cascades as advertised by the
ICON, NAM, and HRRR 925 mb temperatures, further enhancing
confidence. The only lacking piece of evidence resides with 850 mb
winds, which are only around 45 mph as advertised by the GFS, NAM,
HRRR, and the ECMWF. Winds will also be breezy across the Lower
Columbia Basin and Blue Mountain foothills this afternoon, but are
expected to stay below advisory level and hover between 30-40 mph.
The NBM showcases a 70-90% chance of wind gusts of 39 mph or greater
over the Basin and foothills this afternoon, but this may be a bit
inflated when taking into account the lack of 850 mb winds. Thus, it
is expected that the higher winds through the Gorge will slow as the
terrain becomes less variable in the Basin.

Flow aloft will stay predominately out of the west-southwest on
Wednesday as another transient upper level ridge builds across the
area. This more zonal flow will provide cooler overnight
temperatures in the mid-to upper 40s across the Basin, as
Wednesday`s high temperatures drop 4 to 8 degrees from Tuesday.
Wednesday morning temperatures across Central Oregon will be
slightly cooler, with lows dropping into the low to mid-40s.
Breezy winds are again anticipated on Wednesday along the Gorge
and Kittitas Valley, with gusts of 25-35 mph likely (70-80%
confidence). A large upper level low pressure system will
approach the British Columbia coast on Thursday, which will
steadily increase winds through the day. By the evening hours,
wind gusts of 20-30 mph will arrive as a cold front passes. The
large approaching system will also lead to flow aloft turning more
southwest and enhancing to allow high temperatures to rebound
back into the mid-to upper 80s across lower elevations of the
Basin and foothills - which is 6-8 degrees above normal. 75


.LONG TERM...Friday through Tuesday...There is excellent ensemble
agreement (99-100% chance) that a deep, upper-level closed low
centered over the Northeast Pacific Ocean will propagate east-
southeastward towards the Pacific Northwest on Friday. In response,
onshore-directed pressure gradients will increase resulting in
westerly gap flow across the Columbia and Deschutes plateaus. As for
precipitation, while areas east of the Cascade crest will be
shadowed, there is a chance (25-50%) of light rain along the WA
Cascade crest Friday afternoon and evening.

Saturday through Tuesday, ensemble concensus loosens regarding the
evolution of the aforementioned low, and any attendant shortwaves,
as it tracks into the Pacific Northwest.

Delving into possible forecast scenarios, Saturday, ensemble
clusters range from a deep closed low overhead (10% of members) to a
weaker open-wave trough across Washington and southern Canada (35%
of members). Sunday, most ensemble members (75%) advertise the upper-
level trough over the Pacific Northwest, while the remaining 25% of
members suggest the main upper low will track north of the forecast
area. The latter scenario would be warmer and drier than the favored
outcome (cool and unsettled). The unsettled pattern is still the
most likely outcome (75% of members) Monday, though cluster
scenarios diverge regarding pattern details; the favored scenario
among the range of unsettled patterns is the upper-level closed low
overhead (45% of members). This would result in the coolest
temperatures and showery weather across the region.

Breezy to windy westerly gap winds Friday and Saturday will be the
primary instigator of any potential highlights. Both days, 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 system will have the potential to bring rain to the
forecast area Friday through Tuesday, chances of wetting rain (0.1"
or higher) are low through the period (<35% chance), with the
exception of the Cascade crest (35-65% chance, highest for WA).

Due to aforementioned ensemble spread leading to uncertainty in
exact pattern details, confidence is low (20-40% chance), but the
combination of cold temperatures aloft and low PWATs may facilitate a
late-season freeze Sunday and Monday mornings in freeze-prone
locations of central and northeast OR. Plunkett/86


&&

.AVIATION...12Z TAFs...VFR conditions are very likely (95-100%
chance) at DLS/YKM/PSC/PDT/ALW, and likely (75-85% chance) at
BDN/RDM through the period. Should sub-VFR conditions materialize,
it would be due to post-frontal BKN-OVC low-level stratus (015-030
AGL) Tuesday evening and night in the wake of a dry cold front. An
upper-level low and aforementioned cold front will induce westerly
to northwesterly winds of 15-25 kts accompanied by gusts of 25-40
kts this afternoon and evening. Aside from the low probability of
low-level stratus, clouds will be limited to FEW-SCT cirrus.
Plunkett/86


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  83  46  77  46 /   0   0   0   0
ALW  86  50  78  49 /   0   0   0   0
PSC  88  52  81  51 /   0   0   0   0
YKM  83  45  79  46 /   0   0   0   0
HRI  86  49  81  49 /   0   0   0   0
ELN  74  45  73  46 /   0   0   0   0
RDM  81  41  76  42 /   0   0   0   0
LGD  82  43  74  44 /   0   0   0   0
GCD  85  45  79  46 /   0   0   0   0
DLS  79  50  80  50 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 9 AM this morning to 11 PM PDT this evening
     for ORZ041.

WA...Wind Advisory from 9 AM this morning to 11 PM PDT this evening
     for WAZ024-026-521.

&&

$$

MORNING UPDATE...83
SHORT TERM...75
LONG TERM....86
AVIATION...86