418
FXUS66 KMFR 092132
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
232 PM PDT Sun Mar 9 2025

.DISCUSSION...Satellite image shows a thin layer of high level
cirrus moving from southwest to northeast. The cloud deck is a bit
thicker over the marine waters.

It will be dry the rest of today, and possibly into the early part
of next week. As mentioned in previous discussions the upper flow is
splitting with an upper low digging south west of the California
coast. The one grey area where there could be a limited amount of
precipitation will be over the marine water, north coast, and
northwest Douglas County. A few of the individual ensembles show
what would amount to trace amounts of precipitation tonight into
Monday morning, but the precip field basically gets washed out,
meaning trending towards nothing. This is something to be expected
in a split flow pattern. As is typical the NBM does not appear to
take this into consideration due to perhaps a bias correction as
opposed to what the upper pattern is being depicted by the various
operational models, individual ensemble members, and the clusters.

Therefore the forecast will lean on the dry side through Monday
except for the areas mentioned above, and would not be surprised if
it remained dry into the start of next week.

The operational models and individual ensemble members are trending
drier on Tuesday and it could actually end up dry because we could
see brief upper ridging as the upper trough outside of 130W begins
to dig with the surface low deepening.

The main event for the forecast period will be Tuesday night. There
is still the potential for a strong low to develop late Tuesday
afternoon and night, then move inside of 130W Tuesday night into
Wednesday. The only difference is there`s good agreement the track
of the low is farther northwest. If this remain the case, then the
odds of wind impacts will be less, but non the less still exist and
precipitation amounts will be lower. The net result will be a strong
front reaching the coast Tuesday night, then moving inland during
the day Wednesday.

Active weather will return Tuesday night and could last through next
weekend. The next frontal system offshore will move onshore Tuesday
night into Wednesday. High confidence continues for another period
of impactful, potential advisory winds in the Shasta Valley and over
the East Side with winter impacts during the day Wednesday over the
mountains (Cascades/Siskiyous) above 4500 feet. The main frontal
band and upslope precipitation will shift through southwest Oregon
and NorCal Wednesday into Wednesday evening maintaining snow above
about 3500-4000 feet, though snow levels could lower to around 3000
feet Wednesday morning near Mt. Shasta City. The main thrust of
precipitation shifts east of the area Wednesday night into Thursday,
but post-frontal showers continue in onshore flow behind it. Storm
total snow accumulations of 8-16 inches are likely above 3000 feet
with 12-20 inches above 5000 feet. Additionally snow will be
moderate to heavy and wet, with snowfall rates getting close to an
inch or more per hour Wednesday into Wednesday evening. This will
also bring winter impacts to I-5 near Siskiyou Summit and around Mt.
Shasta City. Given the increasing confidence of significant snow
impacts in and around Mount Shasta, a Winter Storm Watch has been
issued. Please see WSWMFR for more details. Highways 97 and 140 are
also likely to be snow covered and slippery by Thursday morning,
when snow levels drop to around 2000 feet.

Active weather is likely to continue Thursday into next weekend.
First, the upper trough will swing through Thursday maintaining a
showery pattern, with highest chances near and west of the Cascades.
This will be followed by a warm front moving across the region
Friday/Friday night with another round of potentially impactful
south winds and rain/mountain snow. Models are then showing a deep
low pressure forming offshore Saturday and moving into the PacNW
Saturday night into Sunday. -Petrucelli


&&

.AVIATION...09/18Z TAFs...VFR conditions prevail across most of the
region with a thin layer of high level cirrus streaming over. Marine
layer stratus and MVFR is currently over the coastal waters and over
areas of the coast, including near Brookings. These conditions will
prevail through this morning. LIFR is present in the Umpqua Basin,
including Roseburg, with low ceilings and wavering visibility, and
this will lift in the afternoon.

Gusty winds develop today in response to an approaching front, with
strongest winds in the afternoon and into the early evening. Winds
will be strongest along the coast, east of the Cascades and in the
Shasta Valley. The front will stall along the coast roughly near
North Bend, bringing some light precipitation this afternoon into
tonight. The front will split before moving inland, so gusty winds
will be the main impact for inland locations. Winds ease this
evening, after sunset. MVFR and local IFR conditions will develop in
rain along the coast and into northwest Douglas County Sunday night.
-CC/Hermansen


&&

.MARINE...Updated 200 PM PST Sunday, March 9, 2025...Gusty south
winds and a moderate west swell will maintain steep seas through
tomorrow morning. Conditions improve tomorrow afternoon into
Tuesday, then an approaching low level system will bring another
round of gusty south winds and west swell. The exact wind/sea
conditions depend on the movement of the low pressure system.
Current deterministic guidance keeps the low farther to the
northwest than previous forecasts. This has decreased expected winds
on Tuesday and Wednesday, keeping gusts below gale strength but
keeping periods of very steep and hazardous seas possible in all
waters, especially Tuesday night. Probabilistic guidance keeps a 20%
chance of gale gusts in the forecast for Tuesday evening into
Wednesday morning. The track of this low will be watched closely as
midweek approaches.

Marine showers and steep seas look to continue beyond this first
system to next weekend. Another low pressure system could approach
next Sunday, affecting sea conditions into the following week. -
TAD/Hermansen


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...Winter Storm Watch from late Tuesday night through Wednesday
     evening for CAZ080-082-083.

Wind Advisory until 5 PM PDT this afternoon for CAZ081.

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT Monday
     for PZZ350-356-370-376.

&&

$$