Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 221116
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
416 AM PDT Fri Mar 22 2024

.DISCUSSION...The weather continues to transition to a wet and
active pattern today, as an offshore low just north of 40N 135W
sends a frontal system through the region. Currently, we have a
warm front lifting north offshore of Washington State and a cold
front moving northwest that will move ashore later this morning.
Precipitation has started along the immediate coastal areas per
recent radar imagery, and widespread precipitation will spread
inland this morning into the afternoon for areas west of the
Cascades, and this afternoon into the evening for areas eastward.

The heaviest precipitation will be across Curry and western and
south-central Siskiyou counties, with moderate precipitation
amounts (generally 0.75 to 1.5 inches) expected today with the
passage of the surface cold front. Snow levels at 5500 to 6000
feet this morning into the afternoon will gradually lower west to
east late this afternoon into the evening as cold air behind the
front settles into the region, but the majority of snow today is
expected to be isolated to the mountains (Cascades, the mountains
of western and south-central Siskiyou County, and the higher
Warner Mtns). Brisk southerly flow ahead of and along the front
will lead to some gusty winds over higher terrain and in the
Shasta Valley in the 15 to 20 mph range with gusts generally to 25
to 35 mph. The Shasta Valley has about a 50% chance to see gusts
to 45 mph today, but with upper level winds in the area looking to
max out at around 45 kt these gusts would likely be infrequent
and not long- duration. Milder but breezy winds are expected along
the coast and in the south Rogue Valley today.

As mentioned, cold air behind the front will lead to snow level
dropping later late this evening into early Saturday morning to
3500-4000 feet. With plenty of showery precipitation behind the
front, particularly in southern Siskiyou County, this will lead
to some snow impacts in the area. A Winter Weather Advisory has
been issued for western and south-central Siskiyou County for
areas above 4000 feet from late this evening to early Saturday
morning, with impacts mainly over the mountains including Highway
89 near Snowman`s Hill Summit and higher portions of Sawyer`s Bar
Road. Precipitation will also likely transition to a rain-snow mix
or wet snow early Saturday morning for areas of Interstate 5 near
Mt. Shasta City as snow levels lower locally, which could result
in light accumulations along the road, particularly near Black
Butte Pass. Roads are still warm from recent good weather, so
impacts are expected to be limited.

Cold air behind the front will also increase atmospheric
instability, bringing a slight chance for some thunderstorms along
the coast and into the coastal mountains today (15-25% chance),
and inland areas west of the Cascades in the late afternoon and
early evening (10-20% chance). -CSP


PREVIOUS LONG TERM DISCUSSION...Sunday morning through Thursday
evening.

Starting on Sunday, the upper level wave impacting us will remain
overhead with showers persisting in Monday.  This will result in
pretty minimal precipitation accumulation with up to 1 inch of snow
in the mountains and under 0.1 inches of liquid below the snow
levels.  High pressure should begin to build by early Monday
morning, which will really push down shower activity and give a
brief break before the next wave begins to move in.  This is shown
in the ensemble data with Monday as a relative dry time.

By Tuesday,  the next wave should be approaching with some higher
Integrated Water Vapor transport values hitting the region under a
strong north to northwest upper level jet.  These values are about
250, which isn`t all that strong for an atmospheric river.  The NBM
has a persistent high probability of precipitation for Tuesday with
the highest chances along the coast and snow levels around 4500
feet.  Again Tuesday doesn`t look good for major weather impacts at
this point.

Things become a little more interesting by Tuesday night as a
surface low builds in the Pacific.  Where this low ends up is a
little uncertain, but it seems fairly reasonable it will be to our
northwest.  This will result in the region being under some warmer
southwest flow with snow levels pushing up a bit to 5000 feet as a
warm front, or leading edge of an atmospheric river hits us.  The
cold front should eventually swing through with snow levels dropping
to 3000 feet around Monday.  There could indeed be some impacts with
this low and system moving through.  The latest snow forecast
between 12Z Wednesday and 12Z Thursday shows between 12 to 16 inches
of snow at Crater Lake with up to 22 inches in a worst case
scenario.  This amount of snow in the mountains over 24 hours could
bring high impacts, although given the time of year and higher sun
angles, it seems a more moderate impact event with some driving
difficulties.

Otherwise,  the cool and wet pattern appears to continue into
Thursday and perhaps even into next weekend. Weather impacts appear
to be limited, although there could be some moderate impacts on
Wednesday with the system hitting the region. -Smith

&&

.AVIATION...22/12Z TAFs...Low level wind shear will be possible for
North Bend airport early this morning. VFR conditions prevail across
the region and will do so into the early morning hours. A front is
arriving at the coast and will push onshore Friday morning. This
will bring lowering conditions (MVFR, potentially brief periods of
IFR under frontal precipitation), widespread terrain obscurations
and gusty winds. The strongest winds are expected Friday afternoon
east of the Cascades and in the Shasta Valley. -Schaaf/BR-y

&&

.MARINE...Updated 300 AM Friday, March 22, 2024...A
persistent gusty south wind will result in conditions hazardous to
small craft for much of the waters through this evening. An upper
level low pressure will approach the region late tonight and linger
over the waters through Saturday before pushing inland on Sunday.
This will bring periods of increased southerly winds tonight into
early Saturday, with isolated and occasional gale force gusts
possible. In addition, seas will become very steep with a dominant
wind-driven sea state mixed with a lower westerly swell at 14
seconds. A hazardous seas warning has been issued for these
conditions from 8PM Friday through 11AM Saturday. Lastly, colder air
aloft associated with the upper low could bring isolated
thunderstorms Friday night into Saturday.

After the front passes, winds become westerly Saturday and then
northwesterly on Sunday. Winds will begin to subside, but remain at
advisory levels during this time with steep waves continuing into
Sunday.

The pattern will remain active going into next week with very steep
seas possible by the middle of next week. That said, there are
timing differences and strength issues between long range models, so
uncertainty remains high at this time for the end of this forecast
period. -Schaaf

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...Winter Weather Advisory from 8 PM this evening to 5 AM PDT
     Sunday above 4000 feet for CAZ080>083.

PACIFIC COASTAL WATERS...Small Craft Advisory until 8 PM PDT this
     evening for PZZ350-356-370-376.

Hazardous Seas Warning from 8 PM this evening to 11 AM PDT
     Saturday for PZZ350-356-370-376.

&&

$$


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