878
FXUS66 KMFR 121119
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
319 AM PST Wed Feb 12 2025

...New Aviation Section...


.AVIATION (12Z TAFs)...

VFR conditions will likely be common through most of this TAF cycle
minus KLMT through this morning (eventually getting to VFR). Then it
gets complicated tonight as area of low pressure moves into the
region bringing lower ceilings and showers. Showers could result in
MVFR conditions tonight but confidence is low in this regard as
there is dry air to overcome in the lower levels. That said, we
will see an increase in cloud cover today and an increase in wind
speeds by tonight.

-Guerrero

&&

.PREV DISCUSSION... /Issued 253 AM PST Wed Feb 12 2025/

DISCUSSION...A very dry and cold air mass is in place over the
region this morning. Satellite imagery shows some patchy low
clouds in the Shasta Valley, lower Klamath Basin and across the
Christmas Valley, but the more impactful element is the very cold
temperatures across the region. Values east of the Cascades range
from the single digits to 15 degrees below zero, while values
across West Side Valleys range from the teens to low 20s. Even
along the coast, freezing temperatures are expected this morning,
and a Freeze Warning remains in effect for communities along the
immediate coast. Several more degrees of cooling are expected
across the area between now and sunrise, and Cold Weather
Advisories are in place for all of the forecast area, with the
exception of the coast south of Port Orford. Details can be found
at NPWMFR.

Dry conditions will persist through much of the day, though expect
increasing cloud cover as the first impactful system approaches the
region, and the weather pattern transitions back to a more active
pattern. This increasing cloud cover will to moderate overnight
temperatures tonight, so we`ll trade the frigid temperatures for the
return of gusty winds and precipitation tonight into Thursday.

There`s pretty good agreement on a front arriving late tonight/very
early Thursday morning and pushing inland through the day Thursday.
The associated low pressure looks to move onshore along the southern
Oregon Coast, and this will send the bulk of the precipitation into
northern California. This looks like a typical southerly flow system
with the more impactful weather expected across Siskiyou County,
with lesser but still impactful weather expected north of the OR/CA
border. Snow levels are expected to rise with this system, but there
is some uncertainty regarding how fast this happens. Initially, snow
levels will be down to around 1000-1500 ft when precipitation
arrives, gradually rising to around 3500-4000 ft by Thursday
afternoon. Given the early morning arrival time, it`s not out of the
question that some West Side Valleys see some light snowfall (0.5-
1.5 inches) early Thursday morning before transitioning to rain
later in the morning, especially for the Illinois Valley, the I-5
passes north of Grants Pass and potentially even into the Umpqua
Basin. A Winter Weather Advisory is in place for portions of the
Illinois Valley, including Hayes Hill, as well as portions of I-5
where confidence was higher for some minor winter weather impacts.
For the Umpqua Basin, expect mainly a light rain/snow mix changing
to rain by early Thursday morning. However, we also monitoring a
slight chance for light freezing rain in far northern Douglas County
late Wednesday night and early Thursday morning. Precipitation
amounts would be very light and models indicate this potential (10-
20% chance) is mainly near and north of Drain. We will continue to
monitor and update for this potential.

As for here in the Rogue Valley, there are some factors going
against snow potential...model 850 temperatures look to be too warm,
hovering around -1 degrees C to +1 degrees C and we typically need
values at or below -3 degrees C. Also, we`re expecting some breezy
southeast winds in the valley, which not only tends to limit
precipitation, but also keeps temperatures warmer due to downsloping
effects. The question will be how far north in the valley do these
winds reach? It could be gusty in Ashland (warmer/drier?) while
winds are calm at the Medford Airport (colder/wetter?), leading to
conditions more favorable for snow in Medford vs Ashland despite the
higher elevation. The HREF, however, would suggest the opposite of
this, indicating snow towards the Ashland are with rain in Medford.
In fact, the HREF even suggests rain for the Illinois Valley and
Umpqua Basin, but maintains snow for areas above 2000 ft and
surrounding foothills. With the cold air in place, am skeptical that
all precipitation starts out as rain for West Side Valley floors.
Needless to say, this is a complicated pattern, and demonstrates the
complexities of forecasting low elevation snow for areas west of the
Cascades. In the Rogue River, Wimer, and Gold Hill areas, cold air
tends to linger longer and could for light snow. Confidence is low
in the exact details of the snow levels and precipitation amounts
before snow levels rise for this area. Regardless of if
precipitation starts out as snow or not, snow levels will gradually
rise through the day Thursday, and should all be rain for West Side
Valleys by late morning/afternoon hours.

Given the southerly flow nature of this system, we have higher
confidence for winter impacts in the Mt Shasta City region where we
currently have around 4-8 inches of snow in the forecast from 10 pm
Thursday - 4 am Friday, with 12 to 18 inches for areas above 4500
ft. A Winter Storm Warning remains in place for these expected
impacts. For the same time frame, we have generally 1 to 3 inches in
the forecast for areas east of the Cascades with the exception of
the Highway 97 corridor from Chiloquin northward where the current
forecast has 3 to 5 inches. Meanwhile, the Cascades will see a
healthy dose of snow accumulations as well, but more in the Advisory
range of 6 to 10 inches. Winter Weather Advisories are in place for
portions of the Cascades and East Side, and details can be found at
WSWMFR.

In addition to the return of rain/snow, we`ll see gusty winds return
to the area, especially along the coast, east of the Cascades and in
the Shasta Valley. Mid level winds are expected to peak around 45-55
kts through Thursday morning, so while we aren`t expecting any
warning level winds, there are Wind Advisories in place for portions
of the Shasta Valley and southern end of the Rogue Valley. Gusts of
25-35 mph will be common in the windy locations, with gusts up to 45-
50 mph are possible for the higher terrain and advisory locations.
Winds will ease Thursday afternoon, but remain breezy into Friday.

Late Thursday into Friday, the trough axis swings through the
region, bringing widespread showers and snow levels around 3500 to
4000 feet. Continued moderate to heavy snowfall is likely across
higher elevations in Siskiyou county during this time along with
light to moderate snow in the Siskiyous, Cascades and across the
East Side. We should catch a break in the weather for much of the
day Saturday before the next system approaches Saturday night into
Sunday. This system will track farther north than the upcoming
front, with low pressure moving inland into Washington. This will
bring higher snow levels late in the weekend/early next week, around
5000-6000 ft or so, as well as another round of gusty winds. The
best chances for impacts from light to moderate snow will be over
the higher passes and in the mountains. Also, given this will be a
westerly flow system (vs southerly like the one expected tonight),
expect higher snowfall amounts for the Cascades late weekend into
early next week. Stay tuned as the time draws near. /BR-y

AVIATION...12/06Z TAFs...Freezing fog has already built into
Klamath Falls/KLMT this evening. Elsewhere, models suggest the
ground is a little to warm and the air a little to dry for fog to
form over other TAF sites. We could see some visibility restrictions
with mist forming overnight. VFR conditions are anticipated on
Wednesday once the fog clears out.  There will be a chance at
showers along the southern Oregon coast later Wednesday evening.

-Smith

MARINE...Updated 230 AM PST Wednesday, February 12, 2025...A
frontal system with gales and steep to very steep seas is expected
to arrive this evening and then push through tomorrow. There still
remains some uncertainty with the strength of the winds and how far
in towards the coast those potential gales could reach. Confidence
is highest for gales in the outer waters, especially south Cape
Blanco. Once this low pressure system pushes east, large long period
swell will follow for all coastal waters Thursday night into Friday
which is expected to build seas to around 14-17 feet at 15-17
seconds. This will at least maintain hazardous conditions to small
craft through Friday night.

BEACH HAZARDS...Updated 230 AM PST Wednesday, February 12,
2025...In the wake of an upcoming low pressure system, a long period
west to southwest swell train will move in likely resulting in
hazardous breaking waves in the surf zone Thursday night into
Friday. Guidance is consistently showing marine waves in the 14-17
foot range. This combined with wave periods in the 15-17 second
range would bring large breaking waves of 20-24 feet to area surf
and beaches. These waves could wash over rocks/jetties and into
normally dry areas. Beach erosion is also possible. Use extra
caution if you plan to visit area beaches late this week.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Cold Weather Advisory until 9 AM PST this morning for ORZ021-
     023>031.

     Wind Advisory from 10 PM this evening to 9 AM PST Thursday for
     ORZ026.

     Freeze Warning until 9 AM PST this morning for ORZ021-022.

     Winter Weather Advisory from 10 PM this evening to 8 AM PST
     Thursday for ORZ024-027>030.

CA...Cold Weather Advisory until 9 AM PST this morning for
     CAZ080>085.

     Winter Storm Warning from 10 PM this evening to 4 AM PST Friday
     for CAZ080-082-083.

     Wind Advisory from 10 PM this evening to 9 AM PST Thursday for
     CAZ081.

PACIFIC COASTAL WATERS...Small Craft Advisory from 10 PM this evening
     to 4 AM PST Saturday for PZZ350-356-370-376.

     Gale Warning from 7 PM this evening to 10 AM PST Thursday for
     PZZ370-376.

&&

$$