FXUS66 KMFR 111138

Area Forecast Discussion
National Weather Service Medford OR
338 AM PST Mon Dec 11 2023


.AVIATION...11/12Z TAFs...A weakening front will keep the
precipitation through parts of this morning. It will fall mainly as
rain from the coast to the Cascades, but with lighter amounts and
mixed precipitation also from the Cascade crest across northern
portions of south central Oregon. Freezing levels will be around
7000 to 8000 feet.

This is producing a wide range of conditions with areas of IFR near
shore, and patchy MVFR, but mainly VFR ceilings inland. Ceilings
will thicken and lower into the early morning with areas of mountain
obscuration increasing.

Showers will gradually taper off through the morning, but low level
moisture will linger with areas of MVFR persisting into the
afternoon. More widespread valley LIFR/IFR with a stabilizing air
mass is likely tonight. -DW/Hermansen


.PREV DISCUSSION... /Issued 315 AM PST Mon Dec 11 2023/

DISCUSSION...Radar is showing isolated to scattered light
showers still moving through the area at this time. One shortwave
disturbance is exiting to the southeast early this morning, while
another upper trough will swing through the area this afternoon
and evening. While this will keep some showers going, we should
see an overall decrease in shower coverage through the day and
especially tonight as the trough settles into the Great Basin.
Upper ridging offshore will move in over the area Tuesday into
Wednesday resulting in a period of dry weather, though there is
the expectation of nighttime/morning low clouds/fog, especially in
the valleys west of the Cascades. Overall, temperatures should be
fairly typical for early December, if not averaging a little above

The next front will approach the coast and try to move onshore
Wednesday night, but upper support for the front will be lacking
and focused off to our north. As such, the front will fall apart
before it can move very far inland. A period of rain is still
likely (60-80% chance) over the coastal waters and from about Cape
Blanco northward along the coast during this time frame, but PoPs
drop off significantly farther inland, down to 20% around
Roseburg. Areas east of there probably won't see any rain from it
at all.

By Thursday, the flow aloft will become southerly and this will
force the front to move back to the north as a warm front
offshore. This will also allow the upper ridge to rebuild
resulting in dry weather through Saturday. Overall, expect
above normal daytime temperatures with near normal nighttime lows.
But, low clouds and fog will probably impact this a bit in the
west side valleys.

While this is occurring, a closed low will set up well offshore
of the California coast. Models show this system eventually
opening up and the upper ridge shifting to the Intermountain West.
This will allow some energy to eject to the northeast and
possibly into our area over the weekend. We've largely maintained
the NBM forecast here due to uncertainty with exactly when this
will occur. PoPs do increase across SW sections Saturday night,
and are highest along the coast and western Siskiyou County on
Sunday (30-50% chance). It appears the best chance at
precipitation will come Sunday night into early next week as the
upper level energy shifts through the region. -Spilde


MARINE...Updated 230 AM Monday December 11, 2023...Impacts look to
be relatively minor this week. Winds weaken and turn northerly
behind the cold front early today. A weak thermal trough could build
over waters south of Cape Blanco this afternoon into Tuesday
morning, although wind speeds are not currently expected to be
impactful. Periods of steep seas are possible in waters south of
Port Orford and from 3 nm to 30 nm from shore late this afternoon
into early Tuesday morning.

Quieter winds and seas will follow Tuesday until Wednesday evening.
The next front is expected to weaken as it approaches the area
Wednesday night but it may produce high and steep swell dominated
seas on Thursday. Seas are likely to diminish Friday, then trend
higher next weekend. -DW/Hermansen