Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 250000

Area Forecast Discussion
National Weather Service Medford OR
400 PM PST Wed Feb 24 2021

.Updated Aviation Discussion.

.DISCUSSION...Sunny skies prevail across the forecast area this
afternoon under high pressure. Even with mostly sunny skies,
afternoon temperatures will still be below normal (especially for
areas east of the Cascades) for most areas because of the cold air
mass in place. The air mass will moderate and warm over the next
24 hours, but clouds will increase starting tomorrow as a frontal
boundary pushes from north to south towards the forecast area.
Energy will ride along this frontal boundary through Saturday
morning, bringing rain and mountain snow mainly to areas from the
Umpqua Divide northward. More specifically, we expect
precipitation to be focused north of a line from about Gold Beach
to Glendale to Butte Falls. Snow amounts through Saturday morning
will be a foot+ in the Willamette Pass area, about 10 inches at
Diamond Lake, and about 5 inches at Lake of the Woods. Several
inches are possible at Chemult along Highway 97 and a few inches
are expected at Mount Ashland. Latest data suggests snow levels
will bottom out around 2000-2500 feet between Friday morning and
Saturday morning. The highest chance for impacts to lower passes
(Canyon Mtn Pass on I-5 for instance) is Saturday morning because
all indications are that more precipitation will fall Saturday
morning. That said, we`re talking about 0.1 to 0.2 inches of
precipitation so a few inches of snow at most. Additionally,
impacts to these lower roadways will likely be confined to
nighttime and morning hours when the February sun isn`t
influencing the roadways.

Even though we`re not expecting heavy precipitation with this front,
we do expect hefty winds in the northern and eastern sections of the
forecast area. Exposed high terrain areas from the Cascades eastward
will be windy from Thursday through Saturday morning. Latest model
data continues to show a 60kt+ midlevel jet moving over Lake County
Friday afternoon, and we`ve issued a High Wind Watch for the
potential for 60mph winds there, generally from Christmas Valley
eastward. Elsewhere east of the Cascades, the typical wind prone
areas will see 45mph+ wind gusts (Summer Lake is in the High Wind
Watch). Additionally, blowing dust and low visibility may result
from these gusty winds. Keene

Long Term...Saturday through Wednesday...Precipitation will taper
off Saturday as the trough moves to the east and the upper level
ridge over the eastern Pacific slowly edges inland. The ridge`s
arrival should push a weak warm front through the region, which
could keep some light precipitation in the area Saturday night
into early Sunday morning, but amounts would be light if
measurable at all.

For the rest of the forecast term, confidence is lacking, as model
and ensemble solutions diverge into two basic patterns. The first
scenario suggests that a large trough will dig south towards the
western US, but will break off into a closed low before making it
onshore. The trough then slides farther south and takes up station
off of southern California, keeping our region dry under high
pressure through the remainder of the term. The other scenario is
one where the trough remains intact within the prevailing
westerlies, bringing a chance for light to moderate precipitation to
the Pacific Northwest Sunday night into Monday before quickly
departing into the Great Basin. The GEFS members and the
deterministic GFS heavily lean towards the first solution, while the
ECMWF and its ensembles heavily favor the second. While neither
scenario is favored, there has been a slight movement overall
towards a drier forecast. Thus, spent some time today bringing
precipitation chances in the extended period down, but still kept at
least a slight chance in place for early next week to account for
the possibility of the wetter pattern.

Overall the long term forecast should be rather quiet, and although
there is a possibility for precipitation early in the week,
temperatures should trend near or slightly above normal for early
March. -BPN


.AVIATION...For the 25/00Z TAF Cycle...At the coast and just
offshore. VFR conditions will continue into tonight. A front will
bring lowering ceilings late tonight. The TAF at North Bend shows
MVFR conditions starting 14z tomorrow morning, but there`s a chance
it could develop an hour or two earlier. There`s a good chance
ceilings could lower to IFR for a few hours around 18z tomorrow and
this has been reflected in the North Bend TAF.

Inland westside. VFR ceilings are expected through tonight. Ceilings
will lower to MVFR late tomorrow morning north of the Umpqua Divide,
including Roseburg. The TAF at Roseburg shows MVFR ceilings around
18z, but there`s a chance the higher terrain could be partly
obscured prior to then. South of the Umpqua Divide VFR ceilings are
expected through the TAF period.

East of the Cascades and northern California, VFR conditions will
continue through the TAF period. Gusty winds could be a concern into
early this evening, then again tomorrow afternoon. However, strong
winds are not expected at this time. -Petrucelli


.MARINE...Updated 200 PM PST Wednesday 24 Feb 2021...Offshore high
pressure and a thermal trough near the coast will support gusty
north winds and steep seas south of Cape Blanco. Steep seas will
also affect the northern waters through tonight due to moderate
northwest swell. Winds will weaken Thursday as a weak front moves
through, then strengthen again Friday into Saturday. Seas will
quickly build late Thursday afternoon and Thursday night as heavy
long period northwest swell builds into the waters. Guidance has
backed off on the swell height and are now showing swells peaking
out between 17 and 19 feet 17 at Friday morning. Despite the
decrease in swell height, seas are still expected to be hazardous
and the Hazardous Seas Watch has been upgraded to a Hazardous seas
Warning from 10 pm pst Thursday until 4 pm pst Friday. However seas
could be Hazardous to Small Craft as early as 10 am pst Thursday and
additional refinements will likely need to be made once the current
small craft advisory ends. The reason for this is to keep the marine
headlines simple and thus less confusing. For details on the all the
marine hazards, please see MWWMFR.

High surf will be another concern during this time period. Current
projections show surf between 20 and 25 feet late Thursday night
through Friday afternoon and a High Surf Advisory has also been
issued. Please see CFWMFR for more details.

Northwest swell will gradually diminish Friday evening through
Saturday night. Meanwhile another front will move into the waters
Friday evening followed by increasing northwest winds Friday night
into Saturday morning. Winds will shift northerly Saturday, but will
remain moderate south of Cape Blanco Saturday afternoon as strong
offshore high pressure sets up along with a developing thermal
trough along the southern Oregon coast. North winds will gradually
lower Saturday night. -Petrucelli


OR...High Surf Advisory from 4 AM to 10 PM PST Friday for ORZ021-022.
     Wind Advisory from 10 AM Thursday to 4 AM PST Saturday for
     High Wind Watch from Friday morning through late Friday night
     for ORZ030-031.

CA...Wind Advisory from 10 AM Thursday to 4 AM PST Saturday for
     High Wind Watch from Friday morning through late Friday night
     for CAZ085.

Pacific Coastal Waters...High Surf Advisory from 4 AM to 10 PM PST Friday for PZZ350-356.
     Small Craft Advisory until 4 AM PST Thursday for
     Hazardous Seas Warning from 10 PM Thursday to 4 PM PST Friday
     for PZZ350-356-370-376.

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