Blizzard and High Wind in Washington, November 19 to 20, 2024

Area Forecast Discussion
National Weather Service Pendleton OR
957 AM PST Tue Nov 19 2024

Updated Aviation Discussion

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

Bottom Line Up Front

1. High snow accumulations along the Cascades and Blue Mountains

2. High winds through central, north central OR, along the foothills
   of the southern and northern Blues and John Day Basin.

Winter Storm Warning in effect 4 PM this afternoon through 10 AM
Wednesday for the Lower Slopes of the Eastern Washington Cascades
Crest

Blizzard Warning in effect 4 PM this afternoon through 10 AM
Wednesday for the Upper Slopes of the Eastern Washington Cascades
Crest

Winter Weather Advisory in effect 10 PM this evening through 10 AM
Wednesday for the Northwest Blue Mountains above 4000 ft and the
East Slopes of the Oregon Cascades

High Wind Warning in effect 4 PM this afternoon through 10 AM
Wednesday for the Foothills of the Northern Blue Mountains of Oregon-
Foothills of the Southern Blue Mountains of Oregon-North Central
Oregon-Central Oregon-Foothills of the Blue Mountains of Washington

Wind Advisory in effect4 PM this afternoon through 10 AM Wednesday
for the Lower Columbia Basin of Oregon-Grande Ronde Valley-John Day
Basin

There is a lot going on in the short term as mentioned above. Day of
concern is today through tomorrow morning. Webcams are already
showing snow arriving along the Cascades and in some isolated areas
along the east slopes. This pattern has set up with upper level
westerly flow filled with lots of precipitation and very packed
pressure gradients.

Models are in firm agreement with the upper level low pushing
towards the PacNW from B.C.. Deterministic models show a decent
amount of precipitation headed towards the PacNW ahead of the
system. Westerly flow aloft will continue to bring snow levels to
near 2500-3000 ft allowing for much of the precipitation to fall as
snow along the Cascades and then later the Blue Mountains. 40-60% of
the raw ensembles show there to be upwards of 12+ inches of snow
along the WA Cascades, 60-80% for 8+ inches of snow for the lower
slopes of the WA Cascades and 70-90% for 6+ inches along the OR
Cascades with higher amounts along the Passes and crests. As for the
Blues above 4000 ft, 50-70% show there to be 6+ inches likely. If
you must travel during these time frames, please remember to plan
accordingly, check the forecast as well as tripCheck for road
information.

Not only do we have lots of winter weather highlights for today
through Wednesday, there are also high wind warnings as well as
advisories. Another difference is that these winds ahead of the
front are coming from the east instead of the normal westerly
direction. Looking at the pressure gradient tool, there is a 12-16
mb pressure gradient change across the region. This will lead to
some very windy conditions. In the areas of the high wind warnings,
80-100% of the raw ensembles show the areas to be under 60 mph gusts
with sustained winds of 30-40 mph. Wind advisory areas will see
sustained winds of 25-35 with gusts to 50 mph. Due to the very high
winds along the crests of the Cascades, a blizzard warning is in
effect due to the newly fallen snow. This will makes for hazardous
driving conditions through Snoqualmie and White Passes. Bennese/90

.LONG TERM...Thursday through Tuesday...Wet and windy weather
continues Thursday through Friday night, although winds are not
looking as strong as what we are anticipating over the next 24
hours. The tightest gradients will develop over the southern half of
eastern Oregon as well as the typical SSE gradients that set up in
the fall from the Lower Treasure Valley to the western Blue
Mountains. The probability of 30-40 mph gusts in our southern zones
and the Grande Ronde Valley are 60-80%. Widespread rain is highly
likely. A warm front and an atmospheric river will impact the
forecast area. Snow levels Thursday through early Friday will rise
to around 7000-8000 feet with the exception of the southern WA
Cascades where snow levels will range from 4000-6000 feet.  Both the
GFS and ECMWF indicate the inland IVT as high as 600 kg/m/s by 12Z
Friday.  A bullseye of high QPF (0.85 out of 1.0) is shown on the
ECMWF EFI over the forecast area for Friday afternoon, particularly
over eastern WA. The most likely rainfall accumulations in the 48-
hour time frame (70-100% probabilities) are 0.5-1.0 inch along the
east slopes of the Cascades, the Blue Mountains, and Wallowas and
0.2-0.5 inches for areas in and around the Columbia Basin. There is
a 40-60% chance that precipitation amounts will exceed 1.5 inches
along the Cascade east slopes and the northern Blue Mtns.

The moist southwest flow ahead of the offshore trough will become
more westerly on Saturday and Sunday with showers likely, mainly
over the mountains, but relatively light amounts. There is some
uncertainty on whether the offshore trough will move inland on
Monday as some ensembles (mainly the Canadian members) maintain a
drier westerly flow. The uncertainty in the synoptic pattern
continues on Tuesday. Models vary on solutions of either a shortwave
ridge or a shortwave trough, therefore confidence is low for the
forecast for early next week. Wister/85

&&

.AVIATION...18Z TAFS...VFR conditions will prevail through the
period. MVFR CIGS currently at KDLS will lift to VFR after about 20Z.
Otherwise expect CIGS to be 050-100 for much of the period. Rain
will spread east across the region this evening and overnight. MVFR
CIGS and VSBYS are likely at KDLS and KYKM tonight and Wednesday
morning with the precipitation.

Primary concern is the increasing winds becoming strong especially
at KRDM, KBDN, KALW, KPDT. Tonight into at least early Wednesday
expect SSELY wind gusts 35 to 40 kt, with brief periods of 50 kt
gusts possible...(40-60% chance). With a strong low level Jet in
place, also included a period of LLWS this evening for the four
aforementioned TAF sites. 78

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  47  37  52  36 /  30  90  50  60
ALW  47  38  52  38 /  30  90  60  60
PSC  49  42  55  40 /  30  90  40  50
YKM  41  29  45  29 /  60 100  60  50
HRI  50  41  56  37 /  40  80  40  50
ELN  40  30  44  30 /  60 100  70  40
RDM  44  36  49  34 /  20  60  50  50
LGD  37  31  42  35 /  40  90  70  70
GCD  40  32  45  36 /  60  90  70  90
DLS  46  39  51  39 /  60 100  70  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 4 PM this afternoon to 10 AM PST Wednesday
     for ORZ044-049-505.

     High Wind Warning from 4 PM this afternoon to 10 AM PST
     Wednesday for ORZ507-508-510-511.

     Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Wednesday for ORZ509.

WA...High Wind Warning from 4 PM this afternoon to 10 AM PST
     Wednesday for WAZ029.

     Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Wednesday for WAZ026.

     Winter Weather Advisory from 10 PM this evening to 10 AM PST
     Wednesday for WAZ030.

     Blizzard Warning from 4 PM this afternoon to 10 AM PST Wednesday
     for WAZ522.

     Winter Storm Warning from 4 PM this afternoon to 10 AM PST
     Wednesday for WAZ523.

&&

SHORT TERM...90
LONG TERM....85
AVIATION...85