241
FXUS66 KMFR 222229
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
229 PM PST Wed Jan 22 2025

.DISCUSSION...High pressure aloft is positioned just off the
Oregon and northern California coast late this afternoon.
Meanwhile, a strong surface high is building in east of the
Cascades. This is resulting in strong subsidence over our forecast
area and skies are largely clear, aside from a few high cirrus.
The last couple of days have really dried things out around here
and fog has not been as prevalent as it was last week. With the
high building in tonight, there could be a little more west side
valley fog than the previous couple of nights, but don`t foresee
the widespread fog that plagued us last week. Expect the usual
areas like the Umpqua Basin near Roseburg and the Rogue Valley
near Grants Pass to have several hours of fog/freezing fog late
tonight/Thursday morning. Patchy fog/freezing fog could also
develop here in Medford and portions of the Illinois Valley.
It`ll be another cold one with low temperatures tonight ranging
from 20-30F for the interior west side valleys and 10-20F over the
East Side. Some single digit readings are expected in the Klamath
Marsh area between Chiloquin and Chemult. Coastal areas around
Coos Bay will once again drop to near freezing, but should be a
few degrees higher than last night, so will forgo a freeze warning
since the duration of temps that low won`t be as long.

The high will settle southward along the California coast on
Thursday maintaining dry weather over the area. Models are
showing a bit more cirrus, especially over northern and western
areas as the ridge flattens, but there should still be at least
some filtered sunshine for most. High temperatures will be very
similar to today.

The next upper trough will press southward from western Canada
Thursday night, then move through the PacNW Friday. Since this
system will be moving from north to south with an over land
trajectory, we aren`t expecting much, if any, precipitation.
There could be a few snow flurries over the mountains, but that`s
about it. What it will do, however, is end the pattern of air
stagnation (at least briefly). Our air stagnation advisory has an
ending time of noon PST Friday, which is fine. A strong pressure
gradient will develop across the area and this will bring strong
N-NE winds late Fri/Fri night that will become NE-E Sat. Mid-level
(700 mb) winds are projected to be in the 35-45kt range with even
up to ~55kt over the mountains Fri night/Sat morning. Expect
widespread breezy to windy conditions over the upper slopes/ridges
and also some of the valleys that happen to align with the wind
(Illinois valley). Local fire weather guidance is showing NE winds
in the 25-35 mph range at many of the RAWS sites with gusts of
45-55 mph over the higher terrain. It isn`t often that we need
wind advisories for NE offshore flow, but this may be one where
it`s necessary in some places. Models are showing a strong MFR-
RDD pressure gradient (in reverse compared to what we usually see
with southerly storms). In this case, we`ll see stronger northerly
winds through the Shasta Valley that may also bring very breezy
conditions to Mount Shasta City on Saturday. We`ll continue to
evaluate wind advisory potential. In addition to the winds, there
will also be a much colder air mass moving in from the north, so
this will result in very cold conditions over the East Side. We`ll
be considering a cold weather advisory for the combination of the
cold/wind expected Friday night through Saturday night. Right
now, apparent temperatures near or even below zero are possible
during this period. One other thing we should note is that while
there is a substantial snow pack near and above 5000 feet in the
mountains/Cascades, those that have prescription burn interests
should be aware of the wind potential coupled with potentially
lower RHs as another dry air mass moves in over the weekend. This
could lead to some potential for pile burns to escape. Please use
caution if planning to burn this weekend.

After the upper trough pushes southward into the Great Basin, it
will close off and settle into southern California Sunday into
Monday. This will allow the offshore upper high to flop over into
the PacNW again resulting in a transition back to (you guessed
it) more stagnant conditions. This means more dry weather with
cold nights, mainly sunny days with slightly milder afternoons.
Winds should relax to more typical levels. Fog may not be as much
of an issue this go around because of the drying air mass and the
strong offshore event This pattern looks to last through at least
mid next week. Guidance is trying to show the ridge breaking down
toward the end of next week and some fronts at least trying to
reach the coast at the end of the month/beginning of February.
-Spilde

&&

.AVIATION...22/18Z TAFS...Updated 21Z. Fog has lifted in the
Umpqua Basin and near Grants Pass with VFR prevailing everywhere
this afternoon. Tonight, ridging moves overhead bringing a
better chance for the Rogue Valley to see fog tonight along with
the Umpqua Basin. For now, this has been added to start first near
Roseburg after midnight and develop in the Medford area a few
hours later. -Hermansen/Spilde


&&

.MARINE...Updated 215 PM Wednesday, January 22, 2025...

The thermal trough is strengthening with steep seas south of Coos
Bay, generally beyond 5 nm from shore but also near shore of Cape
Blanco and Gold Beach. North of Coos Bay, steep seas are expected
beyond 25 NM.

There`s good agreement for a further increase with moderate to
strong north winds later in the week through the weekend due to a
strong thermal trough developing along the coast. The probability of
gale force winds being met at some point in time is high and around
55 percent south of Port Orford. Winds should peak in strength
Friday afternoon/night.

-Smith/Hermansen


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until noon PST Friday for ORZ021-023>026-
     029>031.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 10 PM PST Thursday
     for PZZ350-356-370-376.

     Gale Watch from Friday morning through Saturday morning for
     PZZ356-376.

&&

$$

MAS/ANH