524
FXUS66 KMFR 042354
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
354 PM PST Wed Dec 4 2024

Updated Aviation Discussion

.DISCUSSION...Satellite image shows low clouds lingering in portions
of the Umpqua Basin Illinois Valley and in the Grants Pass area. The
low clouds are slowly burning off, but those areas should break out
late in the day before becoming socked in again early this evening.
Elsewhere, it`s clear.

Weak upper troughing will approach the area from the west tonight,
but it will weaken as it runs into the upper ridge. Therefore
precipitation will be limited to the coast, north of North Bend
Thursday morning. Even then rainfall amounts should only amount to a
trace to a hundreths of an inch at best. Thursday afternoon is likely
to be dry.

The one thing the front will do is bring more cloud cover to the
area tonight into Thursday morning, with the cloud cover thickest in
the Umpqua Divide. This should keep temperatures from dropping down
below freezing. Farther south, in portions of the Rogue parts of the
Illinois, Shasta, and Scott Valleys, the cloud cover may not be
sufficient enough to keep temperatures from dropping below freezing,
so we could be dealing with another round of freezing fog later
Wednesday night into Thursday morning. Areas that experience
freezing fog will result in low visibility along with slick driving
conditions for the early morning commute, especially on bridges and
any other elevated roads because of not warming from the ground
below.

Dry weather is likely Friday with upper ridging building into the
area. The main variable will be the extent of cloud cover and will
it be sufficient enough to keep low clouds and fog from forming. For
now, kept it out of the forecast, but this will need to be looked at
again.

A stronger upper trough will approach the area Saturday, with a
surface front pushing into the area. This will bring light to
occasionally moderate precipitation primarily along and west of the
Cascades. Snow levels Saturday morning will be above pass levels,
with snow levels lowering Saturday afternoon to around 6500 feet by
Saturday evening. However, by that time, precipitation will be
lighter which should limit the amount of snow around Crater Lake.
The higher passes should be okay with no snow accumulation during
the day Saturday, but could not rule out up to an inch around
Diamond Lake Saturday night.

Upper troughing remain over the area Sunday with a few showers
possible west of the Cascades. The shortwave moving in from the
northwest withing the upper trough is not expected to have much, if
any over water trajectory which typically results in little to no
precipitation.

There`s still good agreement among the operational, ensembles and
clusters showing upper ridging building back in by the start of next
week and could last into at least the middle of next week with dry
weather likely. A look at the individual ECMWF ensemble members show
8 of 50 members showing any precipitation next Wednesday, and 2 out
of 30 members from the GFS. In contrast the NBM is running too hot
(meaning too high and too far inland with respect to pops). Given
the above, the forecast in the extended through Wednesday will be
less than what the NBM solutions are suggesting.

After next Wednesday, the general consensus is for the weather
pattern to become more active, with cool and unsettled conditions.
-Petrucelli

&&

.AVIATION...05/00Z TAFS...We`ll start off the evening hours with
mostly clear skies, although there is some LIFR stratus lingering in
the Umpqua(RBG) and Illinois Valleys this evening. The probability
of LIFR visibilities and ceilings tonight is about 50 to 60
percent. The reason why it`s not higher is we`ll see some higher
clouds move into the region tonight ahead of the next wave. This
could inhibit fog and stratus formation. However, when the high
clouds are thin, fog usually forms without a problem. The MOS
bulletins are predicting fog in the Rogue Valley(MFR) later
tonight. We think the fog will clear during the day on Thursday as
an upper level wave moves through Oregon.

&&

.MARINE...Updated 200 PM PST Wednesday, December 04, 2024...Light to
moderate winds and relatively calm seas will persist into Friday.
South winds will increase slightly Thursday into Thursday night. A
warm front moves through Friday night with a stronger cold front
following on Saturday evening. The cold front will be followed by
rapidly building seas Saturday night into Sunday, with very steep
hazardous seas likely. Right now, the swell on Sunday is anticipated
to reach up to 17 feet at 15 seconds, which would be a long period
swell. Seas gradually lower into Monday.

-Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 4 AM PST Saturday for ORZ023-024-
     026-029>031.

CA...None.

PACIFIC COASTAL WATERS...None.

&&

$$