Heavy Snow in Oregon, April 10 to 12, 2022

Area Forecast Discussion
National Weather Service Medford OR
324 PM PDT Sun Apr 10 2022

SYNOPSIS...An unusually cold and strong spring storm will bring
strong gusty winds and accumulating snowfall to southern Oregon
and northern California. In general, most of the snow will
accumulate above 2500 feet with some snow falling down to 1500
feet behind the cold front. The snow will be a significant impact
in the Cascades with up to two feet of snow over mountain
roadways. Winds will also bring impacts with blowing snow and
scattered power outages.

&&

.SHORT TERM...

Showers are starting to fill in on radar as the atmosphere gains
some instability with surface heating. The showers and
precipitation overall should increase in coverage as a warm front
moves into the forecast area overnight. A warm front is a slight
misnomer in this case as snow levels barely change and stay
around the 2500 to 3000 foot range. Eventually, the surface low
will hit the central Oregon coastline bringing strong winds to the
coastline and a little more intense precipitation north of the
Oregon and California border. Those wind gusts along the coast are
expected to reach up to 75 mph near the headlands and capes. This
will most likely occur along the coastal jet which can form ahead
of strong cold fronts. The winds aloft don't hint at some of
these higher winds, although they can occur if this coastal jet
indeed forms.

Through the night, the surface low and the 850 mb become stacked
with some relatively warm air being pulled in ahead of the cold
front. Snow rates will pick up during this time as the atmosphere
becomes rather dynamic. Environmental variables aren't that great
with precipitable water around 0.5 inches and IVTs not that
impressive considering what we usually see with winter storms.
This low just seems to be driven by lower level and upper level
dynamics. The most notable weather feature here is the amount of
snow along the Cascades from this evening into Monday. We're
forecasting up to 24 inches of snow in sections of the Cascades.
The NBM 4.1 is feeling reasonably confident here with a 60% chance
to exceed 24 inches in 24 hours in the Central Cascades near
Diamond and Crater Lake ending Monday evening. Given the amount of
snow in short period of time, snow load would be a reasonable
concern. However, most of very high impact events have snow loads
building over multiple storms.

Eventually, the cold front will move into the forecast area
Monday morning. Snow levels are expected to drop down to 1800 feet
during the day on Monday. However, surface temperatures near the
valley floors will end up around the lower to mid 40's during the
later afternoon and evening hours. Usually what happens is we see
graupel showers given the massive amount of instability and warmer
temperatures in the boundary layer. In any case, some snow flakes
could be seen around valley locations like Ashland.

In addition, the warm surface temperatures and cold air aloft will
generate a rather unstable atmosphere. The NBM and model guidance
in general has a 20 to 30 percent chance of thunder west of the
Cascades during Monday. Convective available potential energy is
around 300 J/kg, which is definitely enough for some rumbles of
thunder Monday.

As we move through the day Monday, winds will increase east of the
Cascades by Monday evening into Monday night. In addition snow
will continue to fall along the cold front as it traverses from
the west to the east. Winds will be the most notable weather
feature east of the Cascades, yet there will indeed be some snow,
especially over the higher passes. Blowing snow is a concern and
has been mentioned many places in the our winter storm warning
product.

As we move into Tuesday an upper level trough essentially becomes
stalled over the Pacific Northwest. This will keep us under a
cooler moist flow with precipitation continuing through Tuesday.
We're forecasting another 8 to 12 inches of snow in the Cascades
on Tuesday. Given the upper level pattern, more snow will likely
arrive during the extended forecast period. Read the discussion
below for more information on that.

.Long Term...Wednesday 4/13 through Easter Sunday 4/17...The
upper level trough is expected to have taken up a position right
over the WA/OR state line around the mouth of the Columbia River by
Wednesday morning, and it is likely to remain there in some form
through the rest of the week, and potentially, could tick around
through the remainder of the forecast term.

In other words, the region will remain cool and showery through the
rest of the work week and into the weekend, with temperatures
hovering around 10 degrees below normal for this time of year
(although a very slight and very gradual warmup is possible through
the week). Any number of shortwaves traversing the flow around the
trough could bring periods of heavier precipitation and breezy to
gusty winds, with even a stray thunderstorm or two possible given
the time of year. Unfortunately, any specific timing or detail
remains unpredictable at this time frame, due to their smaller scale
and transitory nature of these shortwaves.  There is however some
trends in the model suites that show that one of the more potent
shortwaves could pass overhead Thursday, with an uptick in winds and
precipitation chances, as well as a reinforcing shot of cold air,
showing up in many of the ensemble runs. The forecast reflects this
trend, but it is very possible that this could change over the next
several forecast cycles.

The longevity of this trough could be due to a blocking ridge
upstream. That is to say, most model solutions show our forecast
area directly under or within the influence of the right-side
anchoring low of an omega block. Models have a notoriously difficult
time with blocking patterns, thus adding even more uncertainty to
what is already an atypical scenario for our region.

That being said, there is the potential for the overhead trough to
finally shove off to the east sometime next weekend, allowing for a
dry and warmer pattern to return. However, some model solutions
maintain the current pattern through the remainder of the forecast
term, thereby keeping us cool with a continuing chance for rain
through the Easter holiday. Given the high uncertainty, no one
solution appears better than another, so next weekend's forecast
reflects a more  "middle-of-the-road" scenario, with some warmer and
drier conditions beginning to reappear by Sunday. -BPN

&&

.AVIATION...10/18Z TAFs...MVFR ceilings are being observed at the
coast this morning, as a warm front spreads precipitation into the
coast and Umpqua Valley. Elsewhere, mainly VFR conditions exist.
Conditions aren't expected to change much today, though expect
increasing terrain obscurations from the coast and inland this
afternoon and evening.

A strong spring storm will bring increasing winds to the coast first
this evening, then inland areas tonight and tomorrow and increasing
turbulence is expected tonight into Monday. A period of low level
wind shear is expected near the coast, and possibly into the Umpqua
Basin, this evening into tonight before stronger winds reach the
surface overnight. Ceilings will lower to IFR and MVFR from west to
east over inland areas this afternoon into tonight. Keene/BR-y

&&

.MARINE...Updated 200 PM PDT Sunday, 10 April 2022...Seas will
remain steep through this afternoon with moderate northerly to
westerly winds. A strong front will move across the Oregon waters
tonight, and this will bring strong south gales and very steep and
dangerous seas. Winds will shift northwest behind the front late
tonight/early Monday morning, and chaotic seas will result, as
residual southerly seas begin to mix with northwest wind waves and
northwest fresh swell. Northwest winds remain at or near gale force
into Monday. Additionally, the weather pattern on Monday will
support isolated thunderstorms over the waters. Seas are expected to
peak Monday evening. Gusty winds and steep seas last through Tuesday
night with active weather continuing through the week. Keene/BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 5 AM to 11 PM PDT Monday for ORZ030-031.
     Winter Weather Advisory until 5 PM PDT Monday for ORZ029-030.
     Wind Advisory from 5 AM to 11 PM PDT Monday for ORZ029>031.
     Winter Weather Advisory until 11 PM PDT Monday for ORZ028.
     Winter Storm Warning until 11 AM PDT Tuesday for ORZ027.
     High Wind Warning from 11 PM this evening to 2 PM PDT Monday for
     ORZ021-022.
     Wind Advisory from 11 PM this evening to 11 AM PDT Monday for
     ORZ023-024.
     Winter Weather Advisory until 11 PM PDT Monday above 2500 feet
     in the for ORZ023.
     Winter Storm Warning until 11 PM PDT Monday above 2500 feet in
     the for ORZ024-026.
     Winter Storm Warning until 11 AM PDT Tuesday for ORZ025.

CA...High Wind Warning from 5 AM to 11 PM PDT Monday for CAZ085.
     Wind Advisory from 5 AM to 11 PM PDT Monday for CAZ084-085.
     Winter Storm Warning until 11 PM PDT Monday above 2500 feet in
     the for CAZ080.
     Winter Weather Advisory until 11 PM PDT Monday for CAZ083-084.

Pacific Coastal Waters...Small Craft Advisory until 8 PM PDT this evening for
     PZZ350-356-370-376.
     Gale Warning from 8 PM this evening to 2 PM PDT Monday for
     PZZ350-356-370-376.
     Hazardous Seas Warning from 2 PM Monday to 5 PM PDT Tuesday for
     PZZ350-356-370-376.