239
FXUS66 KMFR 051736
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
936 AM PST Wed Feb 5 2025

...New Aviation Section...


.AVIATION (18Z TAFs)...

A complicated set of TAFs is underway as precipitation (rain/snow)
impacts the region which will result in IFR/MFR conditions
throughout the day. At times we may see VFR given the isolated to
scattered nature of showers today, but overall difficult flying
conditions are expected throughout the day. Conditions may worsen
for westside terminals overnight with LIFR conditions likely.
Precipitation will be difficult to nail down on timing, so
subsequent amendments are likely today.

-Guerrero

&&

.PREV DISCUSSION... /Issued 925 AM PST Wed Feb 5 2025/

DISCUSSION...Radar is showing scattered showers in Josephine County
and in eastern Curry and Coos counties. This is tracking
northeast and will be reaching parts of the Rogue Valley, mainly
west of Medford, in the next hour. There is also snow in the
Umpqua Basin near Sutherlin with the heavier bands moving over.
The main update this morning was to extend the Freezing Fog
Advisory for the valley through at least 10 AM. The current winter
hazards continue which can be seen at WSWMFR. Today will focus on
the next round of updates for more snow tomorrow east of the
Cascades and in Northern California. -Hermansen

PREV DISCUSSION... /Issued 352 AM PST Wed Feb 5 2025/

UPDATE...Hydrology discussion added. Please see below.

HYDROLOGY...Due to recent rainfall in Modoc County, the Pit
River at Canby is around 11.0 feet and in major flood stage. For
details see the FLSMFR. It is expected to remain in major flood
today into Thursday, then gradually lower Thursday night and
Friday and reach below flood stage Saturday evening. To put the
rainfall in perspective, Alturas already has had 3.25 inches in
just the 1st 4 days of this month. Normal for the entire month of
February at Alturas is only 1.09 inches!

PREV DISCUSSION... /Issued 343 AM PST Wed Feb 5 2025/

DISCUSSION...An upper low is located off the Washington and
Oregon coasts. This is bringing cold and unstable air to the
area. Shortwave disturbances will move around the low and into the
area today and Thursday, resulting in areas of low elevation and
mountain snow, especially near and west of the Cascades and
extending into northern/eastern Klamath County. Additionally,
western valleys may see icy roadways due to not only left over
snow but also cold overnight/morning temperatures that will allow
moisture on roadways to freeze. Areas of freezing fog are also
expected in some western valleys prior to showers arriving and
where winds are light. Otherwise, today through Thursday morning,
the main concern will be around additional snow in showers as a
couple disturbances move through the area. Snow levels will be
down to lower valley floors and may even be down to beaches at
times this morning as showers move into western portions of the
area. Then snow levels may rise to 1000 to 2000 feet in the
afternoon before lowering again to lower valley floors. Even as
snow levels rise in the afternoon, showers moving in may drop snow
levels back to lower valley floors or bring graupel to western
valleys. Models and satellite/radar trends indicate shower
activity will be most concentrated from the coast into the coastal
mountains through early this morning, then increase in intensity
and coverage during the day and evening, spreading into to the
Cascades and eastward. Also with showers, there is a slight chance
for lighting, especially for the coast waters and coast locations.

As a low pressure system approaches the northern California coast
and moisture moves up into the area, a second round of showers is
likely Wednesday night into Thursday morning. The exact position
of this band of showers is uncertain but overall, expect this band
to be located over western portions of the area, mainly from the
coast into the coastal mountains and extending into portions of
Josephine, western Siskiyou and the Southern Oregon Cascades.

Given this cold and showery pattern, we have added winter weather
advisories (NPWMFR) to many areas from the Southern Cascades west
and into portions of Siskiyou and Klamath counties. We have also
continued the winter storm warning over the coastal mountains,
where shower activity is likely to be greatest. Please see the
WSWMFR for details. Travelers are encouraged to stay up to date with
the current weather and road conditions and delay travel if
possible, for areas most affected. If you must travel, be prepared
for winter travel conditions.

Next, attention shifts to a frontal band of precipitation that
arrives Thursday afternoon into Thursday night as a low pressure
system moves onshore over northern California. Models and
ensembles support slight rise in snow levels to 2000 to 3000 feet
during the day Thursday but given this pattern, cold air may be
slow to move out, especially for areas in southwest Oregon. So
snow levels may remain lower for some locations. We will continue
to monitor the track and timing of this system and where the main
band of precipitation sets up. Models and ensembles then indicate
this low will track inland Thursday night across northeast
California while a trough deepens off the coast of southern
Oregon. This will result in cold air advection into areas west of
the Cascades, with lowering snow levels. Meanwhile the band of
moderate precipitation will remain over the area, with the
heaviest precipitation likely for northern California. Some areas
in Coos and northwest Douglas counties may remain mostly dry
while ongoing precipitation is expected for areas south and east.
Additional winter weather headlines are possible during this
period with moderate to heavy snow possible from the Cascades east
and Siskiyou south and areas of moderate snow possible west of
the Southern Oregon Cascades. With the low is expected to track
northeastward into southeast Oregon and northwest Nevada, expect
continued precipitation into Friday morning. We will continue to
monitor this storm with the next set of model runs. Please watch
for additional updates.

A broad upper trough and cold air mass may settle over the area
late Friday into Saturday with areas of light showers. Much colder
temperatures are expected Friday night into Saturday and again
Saturday night. The National Blend of Models supports temperatures
in the single digits east of the Cascades and in the teens to low
30s for west of the Cascades (except for even cooler temperatures
around 10 to 20 degrees for valleys in Siskiyou County).

AVIATION...05/12Z TAFs...Showers will continue to develop over the
marine waters and move onshore through this morning. Fog has formed
in some area valleys, restricting visibility to 1/4 of a mile,
particularly at Grants Pass and Medford. Showers activity could
break up any areas of fog as they pass through. Also worth noting is
that snow levels remain low, so any showers this morning could bring
some additional light snow accumulations, including at Medford and
Roseburg. More widespread precipitation is expected by this
afternoon, with periods of MVFR/IFR possible in heavier showers,
with snow levels remaining relatively low through this evening.

Along the coast and over the marine waters, showers with possible
thunderstorms are expected through the TAF period with conditions
varying from VFR to brief periods of IFR. Guidance shows
precipitation will mostly be rain, however, if showers are heavy
enough, this could drag colder air towards the surface, resulting in
a brief period of a rain/snow mix, all snow or even small
hail/graupel with reduced visibilities under these heavier showers.

East of the Cascades, ceilings and visibilities should remain VFR
through the period. South winds will increase Wednesday afternoon
with peak gusts near 30 kts. -BPN

MARINE...Updated 200 AM Wednesday, February 5, 2025...Broad low
pressure resides off the coast of Washington and northern Oregon.
South winds will increase this morning as a weak front passes
through the region, resulting in a period of steep seas, with very
steep seas north of Cape Blanco. Winds and seas decrease tonight as
low pressure weakens into Thursday. Gusty north winds and steep seas
return Thursday night into Friday as the low pressure center swings
inland, then relatively calm conditions are expected through the
rest of the weekend. High pressure may return early next week, along
with gusty north winds and steep seas, especially south of Cape
Blanco. -BPN/BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning until 7 AM PST Thursday for ORZ023-024.

     Winter Weather Advisory until noon PST today for ORZ021>030.

     Freezing Fog Advisory until 10 AM PST this morning for ORZ026.

CA...Winter Storm Warning until 7 AM PST Thursday for CAZ080.

     Winter Weather Advisory until noon PST today for CAZ080-082.

PACIFIC COASTAL WATERS...Small Craft Advisory until 4 AM PST Thursday
     for PZZ356-376.

     Hazardous Seas Warning until 4 AM PST Thursday for PZZ350-370.

&&

$$