Heavy Snow and High Wind in Washington, April 3 to 5, 2022

Area Forecast Discussion
National Weather Service Pendleton OR
1058 AM PDT Sun Apr 3 2022

.Updated Aviation Discussion.

UPDATE...This morning sees changes beginning as a strong weather
system approaches the area. Satellite imagery show a well
developed low pressure system along the British Columbia and
Pacific Northwest coasts this morning with a long fetch of
moisture feeding the system with a weak atmospheric river aimed
at the Pacific Northwest late tonight and tomorrow. Skies are
mostly cloudy this morning though some clearing is expected over
the Columbia Basin this afternoon before overcast skies return
this evening. Radar shows rain already coming ashore along the
Washington coast and expect that the Washington Cascade crest will
see showers begin later this morning and this afternoon. Amounts
will be light initially with snow levels around 4500 feet. Tonight
will see heavier rain and higher mountain snow will expand to the
Oregon Cascades this evening. Overnight there will be a chance of
rain in the lower elevations and rain and snow likely in the
mountains. The lower elevations will get up to two tenths of an
inch in the wettest locations and generally less than a tenth of
an inch in most locations. The Cascade crest could see as much as
an inch of precipitation with locations above 4000 feet getting
4-8 inches of snow in the Washington Cascades and 3-6 inches in
the Oregon Cascades. Current Winter Storm Warnings for the
Cascades look good and no changes are anticipated. Winds will
become a significant factor from this storm starting late this
afternoon with winds increasing to 10 to 20 mph with gusts to 30
mph. Tonight will see steadily increasing winds with most of the
area reaching 15 to 25 mph with gusts of 30 to 40 mph in the late
night hours. The big forecast challenge today will be whether to
upgrade the current High Wind Watch to Wind Advisories or High
Wind Warnings. Latest model runs have been trending somewhat
weaker than yesterday's runs but will await the 12Z models before
making a decision. Temperatures today looked good and only minor
adjustments were made. Highs will mostly be in the mid 50s to mid
60s with mid 40s to lower 50s in the higher mountains. Forecast
update already out. Perry/83

PREV DISCUSSION... /issued 432 AM PDT Sun Apr 3 2022/

SHORT TERM...Today through Tuesday...The transient ridge that
brought calm and dry conditions to the region tonight is beginning
it's departure to the east. Behind it, a deck of cirrus advancing
ahead of the next weather system is spreading from west to east
across the forecast area and will increase through the early
morning hours.

Today, troughing in the Gulf of Alaska will start to influence
the region by beginning the setup for a wet and strong westerly
flow aloft into the PacNW. At the head of this westerly flow
aloft, an impulse is expected to push across the PacNW with rain
and high mountain snow showers in the Cascades, where a couple
inches of snow accumulations are expected above 4000ft through
this evening. Precipitation is expected to begin in the WA
Cascades by this afternoon, and by this evening in the OR
Cascades. Outside of the mountains, influence from the approaching
robust weather system is expected to see west-southwest winds
increase to 10-20 mph through this evening and persist overnight.

Overnight Sunday through Monday night, the region will be under
the influence of a strong low pressure system that will slide
across southern BC and Alberta. Directly to the south of this
system, a stacked 170kt jet at the 300mb level will move overtop
the PacNW, with strong winds of 50-60kts down to the 850mb level
overtop the forecast area. Strong winds are anticipated to develop
across forecast area beginning early Monday morning through late
in the evening. At this time, model guidance is still between high
end advisory level to low end warning winds across much of the
lower elevations, so will allow the next shift to take one last
look before making determinations on warnings or advisories across
the forecast area. That said, at the minimum wind advisories will
be needed as winds from central OR to Columbia Basin, including
adjacent valleys and the Simcoe Highlands, will see sustained
winds of 30-40mph with gusts up to 55mph through much of the
daylight hours on Monday.

Along with a strong jet max, a weak atmospheric river is expected
to arrive to the PacNW overnight Sunday and through the duration
of Monday. This will see rain and high mountain snow showers
increase in intensity through Sunday night, with snow levels
lowering across the region through Monday and the early part of
Tuesday. Through the duration of this system, the WA Cascades
above 2500ft can expect to see 12 to 24 inches of snow
accumulation with locally higher amounts along the crests and
peaks, while the OR Cascades will see 10 to 20 inches of snow
accumulations above 4000ft. The Winter Weather Watch for these
areas has been upgraded to Winter Storm Warnings above their
respective elevations listed above, and will be in effect from
this afternoon through Tuesday morning. Otherwise, snow showers
will impact the higher terrain of the Blues and Wallowas overnight
Sunday through Monday, with generally 5-10 inches of snow
accumulation expected in those areas. As for the rest of the
forecast area, a chance of rain showers can be expected through
the course of Monday, though the highest rain accumulations of 0.2
to 0.4 inches will mainly be seen along the lower east slopes of
the Cascades, central and north central OR, and the Blue Mtn
Foothills with generally less than a tenth expected elsewhere.
Light snow showers will be possible across central and N central
OR Monday night as snow levels lower to the floor level, though
any accumulations will be less than an inch.

Tuesday, upper level ridging will begin building into the region,
decreasing the mountain snow and rain showers across the forecast
area through the afternoon. At the surface, a low level jet will
linger through the day, with breezy west winds persisting into the
late evening hours. Winds at this time will not be nearly as
strong as Monday, so no wind highlights are anticipated at this
time. By late Tuesday evening, dry conditions will settle into the
region with winds on the decrease.

Cooler temperatures can be expected after today as the robust low
to our north will push in a much cooler airmass into the PacNW.
Though afternoon temperatures today will be in the mid 50s to mid
60s, they will drop mainly into the mid 40s to 50s Monday and
Tuesday. Lawhorn/82

LONG TERM...Wednesday through Sunday...Models are in good agreement
through Friday and then diverge with ECMWF digging a trough over the
region while GFS remains with a more zonal flow. Ensemble models
show a more troughy pattern for next weekend so leaning that
direction with the forecast. A ridge of high pressure centered along
the coast will continue building inland on Wednesday and persist
through Friday. This will be the beginning of a warming trend which
will peak on Friday with highs reaching into the 70s across the
lower elevations. Then the ridge begins shifting eastward in
response to a deepening upper level trough in the Gulf of Alaska.
The trough will nudge inland late Saturday and Sunday increasing the
chance of some precipitation and cooling temperatures.

AVIATION...18Z TAFs...Increasing high clouds with VFR conditions
through the day before a cold front arrives tonight, lowering
clouds, producing precipitation, and increasing winds. CIGS BKN-
OVC 100-250 today, then lowering tonight to 035-050 with onset of
precipitation. Winds today will be 10-12 kts with gusts around 20
kts. Winds will increase later tonight into Monday morning to
15-25 kts with higher gusts, potentially 35-40 kts. Additionally,
LLWS potential will increase beginning around 10Z Monday as a
strong low-level jet of roughly 40-60 kts with a core around 5kft
develops above all TAF sites. Based on forecast soundings,
confidence is low to moderate in criteria being met for LLWS in
TAFs so have opted to omit from the 18Z update. Plunkett/86

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  61  44  56  36 /  10  50  60  30
ALW  63  46  57  37 /   0  60  70  30
PSC  65  50  60  40 /   0  40  30   0
YKM  63  41  54  32 /  10  50  60  30
HRI  65  47  59  36 /  10  40  30  10
ELN  58  38  49  33 /  10  60  70  40
RDM  60  39  52  26 /  10  40  70  40
LGD  59  40  51  31 /  10  60  90  60
GCD  60  39  52  29 /   0  50  50  30
DLS  63  47  55  41 /  10  80  90  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 8 PM this evening to 5 AM PDT Tuesday
     for ORZ509.

     High Wind Watch from Monday morning through Monday evening for
     ORZ041-044-507-508-510-511.

WA...High Wind Watch from Monday morning through Monday evening for
     WAZ024-026>029-521.

     Winter Storm Warning from 2 PM this afternoon to 8 AM PDT
     Tuesday for WAZ520.

&&

UPDATE...83
SHORT TERM...82
LONG TERM....91
AVIATION...86