993
FXUS66 KMFR 231642
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
842 AM PST Mon Dec 23 2024

.UPDATE...

We are seeing some relief in fog across the Rogue Valley, but
conditions are still dense in the Illinois and Umpqua valleys.
Will likely cancel the dense fog advisory here this morning as
conditions continue to improve. Then our attention turns to a few
rounds of potential hazardous weather across the region with
snowfall starting tonight/tomorrow, and then more rounds
continuing through the week, especially for areas above 4000
feet. Christmas day and beyond those snow levels could be slightly
lower, and we will be taking a closer look at that today as passes
could be impacted for holiday travel.

-Guerrero

&&

.MARINE...Updated 800 AM PST Monday December 23, 2024...Very high,
very steep, and chaotic mixed seas will be a persistent feature in
the marine waters through the next week. Multiple strong fronts will
pass through the area bringing multiple rounds of gale force south
winds, with storm force gusts a possibility with each front.
Residual wind wave/fresh swell along with a heavy background west
swell will keep very high and steep combined seas going through the
morning hours today.

The next strong front arrives this afternoon. A deepening low
pressure moves south-to-north near 130W this afternoon and evening,
and this will bring another round of strong gales to the waters.
It`s not out of the question for that some isolated areas experience
a brief period of storm force winds between 3-6 pm local time today.
Seas will build again this afternoon with the addition of very high
and steep wind waves to the ongoing heavy west swell, resulting in
chaotic mix seas into the overnight hours. Winds will ease below
gales tonight, but seas will remain very steep and hazardous for all
areas into early Tuesday morning.

Conditions briefly "improve" as seas lower to around 10 to 15 feet
late Tuesday into early Wednesday morning, but seas will remain high
and steep with conditions hazardous to small craft during this time.
Another deep low pressure system and strong front is expected
Christmas day through Christmas night, then yet another Thursday
afternoon into Thursday night. High end gales look likely with these
fronts, possibly even storm force. Guidance continues to fluctuate
with respect to the height of the swell train behind the Christmas
front, but seas will continue to be very high, steep to very steep,
and chaotic through next weekend.

&&

.PREV DISCUSSION... /Issued 327 AM PST Mon Dec 23 2024/

DISCUSSION...Today, we`re in a relative break in the action
behind yesterday`s and last night`s front with the axis of a
quick-moving short wave upper ridge nearing the coast this
morning. Leftover light rain and mountain snow showers are still
impacting far SE sections of the CWA early this morning, but these
will diminish in the next couple of hours. The break has resulted
in widespread dense fog forming in the valleys west of the
Cascades, which prompted the issuance of a Dense Fog Advisory
through 10 am PST. In many areas, this is reducing the visibility
to below 1/4 of a mile at times. So, if you`re headed out this
morning, please take some extra time, use low beam/fog headlights
and allow plenty of extra space between you and the vehicle ahead
of you.

The short wave ridge axis will push east of the Cascades this
afternoon and pressure gradients will increase quickly ahead of
the next front offshore. So, fog should lift by late morning and
we expect winds to ramp up this afternoon, then especially this
evening. Winds back enough to SSE so that gusty winds should
develop in the south end of the Rogue Valley first and spread all
the way to the airport (maybe just about all of the Rogue Valley
southeast of Gold Hill). Wind gusts of 45-50 mph are possible, so
a Wind Advisory is out for that. Wind advisories are up for the
usual areas east of the Cascades (Highway 31 near Summer
Lake/Valley Falls). We also have a High Wind Warning in effect for
the Shasta Valley, where wind gusts could be 60+mph from Weed to
Montague. It will also get windy at the coast, but similar to the
front two nights ago, gusts to 55 mph should be just shy of
warning criteria. The front itself will pack a punch since it will
be attendant to a strong and deepening surface low that will bomb
out west of Vancouver Island overnight into early Tuesday
morning. A strong core of high PWAT (1.00-1.25 in) air and solid
IVT will accompany the front as it moves onshore during this time
period. Expect a period of moderate to heavy rainfall along the
sharp frontal boundary. Widespread rain amounts of 1-2 inches can
be expected west of the Cascades with locally 3 inches in the
favored coastal ranges of Curry County. West side valleys will
have a little less due to some downslope effects at the start.
Snow levels will start very high (near or even above 8000 feet),
but cold air will be catching up to the back edge of the precip as
the front pushes east of the Cascades during the wee hours of
Tuesday morning. Expect rain to change to snow in the mountains
then, and this could make travel difficult near and over the
Cascades. We are expecting snow amounts of 3-6 inches. Precip
could also change to snow over Siskiyou Summit Tuesday morning
and even portions of the East Side (highway 140 near Klamath
Falls), so if you are planning to travel Tuesday morning, know
there is potential for wintry travel, despite not really being
enough snow to warrant advisories.

Post-frontal showers will linger Tuesday afternoon with the upper
trough axis moving to near the Cascades. Showers diminish
Christmas Eve and, with enough clearing of the higher clouds, you
guessed it, a certain red-nosed reindeer will likely be needed to
guide a Santa`s sleigh through areas of fog/freezing fog
overnight.

The break in the action will last into Christmas Day for most
locations, but another fast-moving Pacific system will move in
with additional rain/wind breaking out along the coast by
afternoon, then spreading inland by evening. Wednesday night into
Thursday will be another wet one. This time, snow levels will be
low enough to support significant mountain snowfall with
preliminary amounts of 10-20 inches in the Cascades/Siskiyous and
Mt Shasta region. Significant accumulation is also possible for
portions of the East Side, especially Winter Rim and the spillover
area along Highway 97 from around Chiloquin northward. Most of
the accumulation should be up above I-5 (above 4000 feet), but a
few inches are possible down to pass level like near Siskiyou/Black
Butte Summits. We`ll probably need some watches/advisories for
this over the next couple of shifts.

Late this week, into the weekend, at least a few more wet fronts
will come in with snow levels rising again. As such, rivers,
creeks and streams will be on the rise. We`ll be monitoring this
for flood potential as we head toward the New Year. Some rivers
are shown to reach action and even flood stage this weekend, so a
flood potential outlook may be necessary at some point. The good
news is that extended guidance (Week 2 after Dec 30) is showing a
trend toward drier conditions. So, while the Pacific faucet is
likely to turn off for a while, it will probably be at the expense
of more foggy nights. -Spilde

AVIATION...23/12Z TAFS...Clear skies and stabilizing atmosphere
behind the most recent front have allowed for LIFR conditions in fog
to develop across West Side Valleys. Meanwhile, east of the
Cascades, MVFR conditions continue, but if enough clearing happens
there could be isolated areas of LIFR conditions that develop. These
conditions will persist through at least sunrise, before gradually
improving during the late morning hours. Another front will affect
the region this afternoon, with showers arriving at the coast then
moving inland on Monday evening. Low level wind shear will return
this afternoon ahead of this next front, and will continue through
Monday night. Additionally, expect strong winds to surface along the
coast, in the Shasta and Rogue Valleys as well as east of the
Cascades this afternoon and evening. As the front moves inland,
expect conditions to lower to MVFR with the development of
widespread terrain obscurations. /BR-y

MARINE...Updated 200 AM PST Monday December 23, 2024...Very high,
steep, and chaotic mixed seas will be a persistent feature in the
marine waters through the next week. Multiple strong fronts will
pass through the area bringing multiple rounds of gale force south
winds, with storm force gusts a possibility with each front.
Residual wind wave/fresh swell along with a heavy background west
swell will keep very high and steep combined seas going through
the morning hours today.

The next strong front arrives this afternoon. A deepening low
pressure moves south-to-north near 130W this afternoon and evening,
and this will bring another round of strong gales to the waters.
It`s not out of the question for that some isolated areas experience
a brief period of storm force winds between 3-6 pm local time today.
Seas will build again this afternoon with the addition of very high
and steep wind waves to the ongoing heavy west swell, resulting in
chaotic mix seas into the overnight hours. Winds will ease below
gales tonight, but seas will remain very steep and hazardous for all
areas into early Tuesday morning.

Conditions briefly "improve" as seas lower to around 10 to 15 feet
late Tuesday into early Wednesday morning, but seas will remain high
and steep with conditions hazardous to small craft during this time.
Another deep low pressure system and strong front is expected
Christmas day through Christmas night, then yet another Thursday
afternoon into Thursday night. High end gales look likely with these
fronts, possibly even storm force. Guidance continues to fluctuate
with respect to the height of the swell train behind the Christmas
front, but seas will continue to be very high, steep to very steep,
and chaotic through next weekend. /BR-y

BEACH HAZARDS...Updated 200 AM PST Monday, December 23, 2024...As
strong fronts continue to progress over the eastern Pacific,
multiple rounds of high and very steep swells will result in
hazardous, and at times, dangerous, surf conditions this week and
into the weekend. Dangerous conditions are expected today with large
breaking waves of 25 to 33 ft expected in the surf zone. A High Surf
Warning is in effect through early Tuesday morning for this.
Conditions briefly improve Tuesday into early Wednesday, but this
improvement will be short lived. Additional fronts will bring the
return of dangerous surf conditions Wednesday night (Christmas
night) through Thursday evening, with hazardous surf conditions
likely to continue into next weekend.

During these events, extremely large breaking waves will create very
hazardous and dangerous conditions along beaches and area
shorelines. Waves will inundate beaches and surge into normally dry
areas. Infrastructure damage and significant beach erosion can be
expected. Stay away from area beaches during this period of active
weather. /BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 7 PM this evening to 4 AM PST Tuesday for
     ORZ026-030-031.

     High Surf Warning until 4 AM PST Tuesday for ORZ021-022.

     Dense Fog Advisory until 10 AM PST this morning for ORZ023-024-
     026.

CA...High Wind Warning from 1 PM this afternoon to 1 AM PST Tuesday
     for CAZ081.

     Wind Advisory from 7 PM this evening to 4 AM PST Tuesday for
     CAZ085.

PACIFIC COASTAL WATERS...Hazardous Seas Warning until 1 PM PST this
     afternoon for PZZ350-356-370-376.

     Gale Warning from 1 PM this afternoon to 4 AM PST Tuesday for
     PZZ350-356-370-376.

     Small Craft Advisory from 4 AM Tuesday to 10 AM PST Wednesday
     for PZZ350-356-370-376.

&&

$$