High Wind in Washington, November 4, 2024

Area Forecast Discussion
National Weather Service Pendleton OR
919 AM PST Mon Nov 4 2024

.MORNING UPDATE...No major changes yet to the overall forecast,
but taking a look at wind products for the region and determining
if a need will arise to upgrade any areas from wind advisory to
high wind warning. The most likely candidate would be the Yakima
Valley. Looking at current conditions though, Rattlesnake Hill in
the Columbia Basin is already showing 72 mph gusts, with some
other peaks in the rest of the region at 30-45 mph. My other line
of thinking is that 21Z (1 PM) may be a bit too late and we might
need to start the highlights a bit earlier. Will continue to
monitor and adjust based on the latest forecast data, but for now
we're definitely going to be seeing the windy day as expected.
Goatley/87

AVIATION...18Z TAFs...VFR conditions expected through the forecast
period. Main concern today will be the windy conditions that will
affect all TAF sites beginning now and 21Z. Winds will range from 15-
30kts through the day with gusts to 40 kts likely, especially in the
wind prone areas of YKM/DLS/PDT. Models and current conditions do
not show any LLWS, however, this is a set up where LLWS could become
a possibility and will be monitored through the day. Bennese/90

&&

.PREV DISCUSSION... /issued 334 AM PST Mon Nov 4 2024/

SHORT TERM...Today through Wednesday...Satellite and radar
imagery tonight are showing the next shortwave trough and frontal
system offshore the PacNW, with light precipitation already moving
across western WA/OR at this time.

Today, an upper shortwave trough and strong frontal system will
push across the PacNW, bringing with it another round of mountain
snow and light rain through this evening. The upper trough will
exit to the east of the region by early Tuesday morning, with
northwest flow aloft developing and persisting over the PacNW
through Tuesday afternoon. The WA Cascades will see the heaviest
snow accumulations late this morning through the afternoon, with
light snowfall persisting through Tuesday morning. In the northern
Blues, light to moderate snowfall will develop with the initial
push of the trough/frontal system by this afternoon, but CAMs are
indicating a weak deformation band developing over far southeast
WA and northeast OR by Tuesday morning, resulting in moderate to
locally heavy snowfall across the interior northern Blues and the
higher peaks of the southern Blues and Wallowas. In the WA
Cascades above 4kft, there is a 70-85% chance of snow
accumulations exceeding 6 inches through Tuesday morning; in the
northern Blues above 4.5kft chances of exceeding 6 inches of
snowfall are 80-90% through Tuesday afternoon. While the upper
slopes of the WA Cascades already has a winter weather advisory in
effect through Tuesday morning, an advisory has been issued for
the northern Blues from late this morning through Tuesday
afternoon. Otherwise, across the remainder of the eastern
mountains and OR Cascades, confidence is high (70-80%) that snow
accumulations will not exceed 4 inches.

The approaching upper shortwave trough and frontal system will
also result in breezy to windy conditions developing across the
forecast area. Pressure gradients at the surface will begin to
tighten this afternoon with the approach of frontal system to the
forecast area, with a strong 45-60kt low-level jet developing on
the lee side of the WA Cascades in the late afternoon. Both
global models and CAMs show a strong signal for the low-level jet
to mix down across areas of the Simcoe Highlands, Kittitas
valley, and while not as strong as the other two regions, the
eastern Columbia River Gorge as well. In these areas, the NBM
shows 24-hr probabilities of exceeding 55mph gusts between 75-85%
by Monday night. For the Columbia Basin, north central OR, Blue
Mountain foothills, and the Yakima valley, the NBM shows 24-hr
probabilities of exceeding 45mph gusts between 80-90% by Monday
night. At this time, do not see a need to upgrade any wind
advisories or extend wind highlights to further zones.

By late Tuesday, the PacNW will come under the influence of an
upper ridge building over the eastern Pacific. As flow aloft
shifts to the north, precipitation chances across the mountains
will taper off, with dry conditions developing Tuesday night.
A strong surface pressure gradient across the region will persist
into early Tuesday morning and will gradually weaken through
Tuesday as the influence of the upper ridge grows over the region.
This will result in breezy to locally windy conditions persisting
through Tuesday afternoon. The upper ridge will move inland early
Wednesday morning and sit over the PacNW through the work week,
resulting in dry and calm conditions. That said, the potential for
fog to develop across the lower elevations and mountain valleys
will increase beginning Tuesday night, though confidence in
location, timing, and extent of areas of fog is low-mod(30-40%) at
this time. Lawhorn/82

LONG TERM...Thursday through Monday...Ensembles in pretty good
agreement on what looks to be a quiet end of the work week before a
more active pattern returns next weekend onward. Thus far, guidance
depicts the start of next weekend's pattern as more SW in nature,
making for limited mountain snow concerns, but that could shift
based on how ensembles evolve towards the end of the period onward.

Not much disagreement across ensemble members with regards to a ridge
overhead Thursday into Friday. We are approaching the time of year
where patchy fog in the valleys may be a concern under high pressure
ridge patterns, however confidence is low on fog developing
overnight through early Thursday and Friday morning (<20%) due to
the relatively transient nature of the ridge, plus dew point
depressions across guidance don't quite support fog development.

By early Saturday morning, ridging is nudged aside by a broad low
based in the Gulf of Alaska that will shift winds aloft more SW.
This will help keep snow levels generally elevated above pass level,
with models currently suggesting around 4000 ft for the WA Cascades
and 4500-5000 ft for the Oregon Cascades and eastern mountains. This
broad Alaskan low will help circulate a series of shortwaves through
the PacNW Saturday onward, which will help eventually trend the snow
levels down more toward 3500-4000 ft, but confidence as of now is
around 50-60% that our major mountain passes will not see impactful
snow through early next week, save for maybe White Pass in WA, but
even then accumulations look to be modest at best at only a couple
inches. The biggest discrepancy across ensembles is the timing of
each shortwave passage, which is to be expected with how progressive
the synoptic pattern looks to be. Evans/74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  55  37  51  26 /  70  20  30   0
ALW  55  39  52  28 /  90  30  40   0
PSC  58  42  56  31 /  80   0  10   0
YKM  57  33  55  25 /  60  10   0   0
HRI  58  42  56  29 /  60  10  10   0
ELN  52  35  50  25 /  80  30  10   0
RDM  53  33  45  24 /  30  10  10  10
LGD  46  35  42  22 /  90  50  60  10
GCD  48  32  41  21 /  70  20  50  20
DLS  57  45  55  34 /  70  20  20  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 1 PM this afternoon to 7 AM PST Tuesday
     for ORZ041.

     Wind Advisory from 1 PM this afternoon to 7 AM PST Tuesday for
     ORZ044-507-508-510.

     Winter Weather Advisory until 4 PM PST Tuesday for ORZ502.

WA...High Wind Warning from 1 PM this afternoon to 7 AM PST Tuesday
     for WAZ024-026-521.

     Wind Advisory from 1 PM this afternoon to 7 AM PST Tuesday for
     WAZ027>029.

     Winter Weather Advisory until 4 PM PST Tuesday for WAZ030.

     Winter Weather Advisory until 10 AM PST Tuesday for WAZ522.

&&

MORNING UPDATE...87
SHORT TERM...82
LONG TERM....74
AVIATION...90