Small Craft Advisory 49, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
1050 PM PDT Mon Apr 18 2022

.Updated Aviation Discussion.

.AVIATION...19/06Z TAFs...The main concern will be the potential for
another round of moderate to strong winds again as early as 17z
until 0z tomorrow east of the Cascades, including Klamath Falls.
They should not be as strong as today, but gusts up to 35 kts ate
possible.

VFR ceilings are expected tonight. However, partial mountain
obscuration is likely from the Cascades west. Ceilings will lower to
MVFR at the coast and just offshore towards daybreak, then IFR
around mid morning tomorrow as another system arrives. This system
will also result in lowering ceilings at Roseburg with MVFR ceilings
towards 13z. Medford should remain VFR, although guidance shows MVFR
ceilings for about a 4 hour period between 18 and 22z and this was
added to the TAF.

East of the Cascades, ceilings should improve to VFR later tonight
and should remain VFR until the end of the TAF period. However
conditions could improve sooner than what's indicated in the TAF
-Petrucelli

&&

.DISCUSSION...Current radar is showing the large band of
precipitation moving along and east of the Cascades. This band of
precipitation has brought periods of moderate to heavy
precipitation, and we've received numerous reports of snow falling
all the way down to 1300 feet in the Illinois Valley during the
periods of heavy precipitation. Behind the front, isolated to
scattered showers are ongoing and should be for the next few
hours with another impulse arriving sometime tonight or tomorrow.
Overall, the current forecast looks reasonable. For more
information, please read the previous discussion below. -Schaaf

&&

.MARINE...Updated 830 PM PDT Monday, 18 April 2022...The front has
moved onshore and winds are diminishing. Some newer data is starting
to come in and there is some evidence of a surface low moving into
the waters Tuesday morning which could bring a brief period of small
craft conditions to the southern outer waters late Tuesday morning
into early Tuesday afternoon. If winds were to reach small craft, it
would only be for 2-3 hour period. We'll wait for some more data to
some in and take another look at this.

Meanwhile seas are still running between 9-10 feet due to a fresh
southwest swell being generated behind the strong front that moves
through the waters earlier in the afternoon. Seas should gradually
diminish overnight tonight.

A stronger front will approach the waters early Wednesday morning
with steep wind driven seas likely until the front moves onshore
Wednesday afternoon. At the very least, conditions will become
hazardous to small craft. However, gale force winds remain possible
during this time. Guidance shows a high, long period swell moving
into the waters early Thursday morning with swell heights peaking
out between 16 and 18 feet with a period between 16 and 17 seconds
late Thursday night. in addition to the waves, some thunderstorms
are forecast over the waters and along the coast Tuesday and again
Wednesday Some storms may be strong.-Smith/Petrucelli

&&

.PREV DISCUSSION... /Issued 502 PM PDT Mon Apr 18 2022/

Updated Aviation Discussion.

AVIATION...19/00Z TAFs...Strong winds east of the Cascades remain a
concern into early this evening, then diminish later this evening
and tonight. There is the potential for another round of moderate to
strong winds again as early as 17z until the end of the TAF period
tomorrow east of the Cascades, including Klamath Falls, although
they should not be as strong as today. Gusty winds at Medford likely
have reached their peak and is expected to diminish over the next 2-
3 hours.

All TAF sites are showing VFR ceilings and this should remain the
case into this evening. However partial mountain obscuration is
likely. Ceilings will lower to MVFR at the coast and just offshore
late this evening, then IFR later tonight as another system arrives.
This system will also result in lowering ceilings at Roseburg with
MVFR ceilings towards 14z. Medford should remain VFR through the TAF
period, although there is a chance for brief periods of MVFR between
0z and 3z in moderate precipitation.

Ceilings will lower to MVFR at Klamath Falls this evening as the
front moves into the area. The TAF shows the lower conditions
lasting into the overnight hours, but ceilings could come up enough
for VFR conditions to return after the front moves through. We'll
continue to monitor. -Petrucelli

DISCUSSION...18/12Z NAM/GFS/EC in.

Clouds are overspreading the Medford forecast area ahead of a cold
front which has just moved onshore. Precipitation has been
reported over most of the west side. Winds have picked up and
have been gusting into the 50s along the coast, in the Shasta
Valley, and east of the Cascades. There are a few locations with
higher gusts, such as Timber Mountain in Modoc County and the ODOT
sensor on Highway 101 near Humbug Mountain, but those locations
historically are among the windiest locations in the area.

The front is and will bring a combination of strong, gusty winds
and moderate rain and mountain snow to the area. Rain and snow
will spread east of the Cascades this evening and tonight. Snow
levels will be around 5000 to 5500 feet today, lowering to around
4500 feet with the frontal passage this evening into tonight, then
down to 3000 to 3500 feet by early Tuesday morning.

There will be moderate to locally heavy snow accumulations in the
Southern Oregon Cascades, mainly above 4500 to 5000 feet, and in
the higher mountains in the Siskiyous, above 5000 feet. Peak
snowfall rates over the Southern Oregon Cascades are expected this
evening and may approach 1 inch per hour. Moderate to heavy
snowfall rates combined with gusty winds, especially in exposed
areas, may result in near white out conditions at times. Winter
Weather Advisories are in effect for above 4500 feet in the
south central Oregon Cascades and above 5000 feet in the Southern
Oregon Cascades and Siskiyous from late this afternoon through
late this evening. See PDXWSWMFR for details.

There will also be moderate snow accumulations across the higher
mountains above 5000 to 5500 feet in Siskiyou county. However,
this will mainly affect remote locations. East of the Cascades,
there will be a mix of rain and snow this evening into tonight,
changing to snow late tonight and early Tuesday morning. Mostly
light snow accumulations are expected, expect for locally moderate
snowfall possible in the higher mountains across far eastern
Klamath into western Lake County and over the Warner Mountains.

As far as winds go, they will be strong and gusty ahead of the
front, diminishing behind the front. The strongest winds from now
through tonight will occur in the Shasta Valley as well as east
of the Cascades over the higher mountains and into the Summer Lake
and Valley Falls areas, with winds gusting to 65 mph. A High Wind
Warning and/or a Wind Advisory remains in effect for these areas.
See PDXNPWMFR for details.

Behind the front, unstable conditions supported by cold air
aloft will bring a slight chance for thunderstorms this evening
into tonight to the coastal waters and coast from around Cape
Blanco north.

Widespread post frontal showers will persist until the supporting
upper trough moves to the east of the area Tuesday. Snow levels
will be down to 3000 feet Tuesday morning, rising to around 4000
to 5000 feet Tuesday afternoon. Showers will be mainly light with
some heavier showers at times, especially over the mountains from
the Cascades west. Then shower are expected to decrease in
coverage and intensity Tuesday evening and Tuesday night.

A short wave ridge will move through Tuesday night, bringing a
relative break in the action, but that break will be short lived.
Another upper trough will move in, pushing another wet and windy
front onshore Wednesday. This one may require another round of
wind related warnings and advisories. There may be another round
of thunderstorms over the coastal waters and along the coast
Wednesday into Wednesday night.

LONG TERM...Thursday Apr 21 through Monday Apr 25 2022. There is
a sense of satisfaction that comes when, in this case, over the
course of a few days, the various model solutions at our disposal
transition into more orderly agreement, allowing for a more
confident forecast to be issued. Active, wet, frontal driven
conditions are expected Thursday through Friday into Friday night.
Building high pressure will dominate our weather during the
weekend with a warming trend and mostly or entirely dry
conditions. Lastly, beginning Monday, there is still confidence in
the big picture, but model differences do become noteworthy. The
influence of the ridge is expected to diminish Monday as it is
pushed farther inland with another broad, deep trough moving
southeast out of the Gulf of Alaska.

A broad trough over the eastern Pacific Ocean will move closer to
the coast on Thursday. The northernmost of the strongest couple of
developing waves associated with the trough will have moved across
our area Wednesday night, weakening as it continues across Modoc
County on Thursday morning. Meantime on Thursday, the southern
portion of that wave and another will be south of our area, tracking
east across northern and central California with heaviest
precipitation for the Sierra Nevada. The result for our area will be
numerous showers and snow showers, mostly light and over the south
to southwest facing higher terrain with snow levels around 4000 to
5000 feet msl. Snow amounts will be mainly up to a couple of inches,
with variability due to the nature of showers. There is also a
slight chance of embedded thunderstorms, mainly Thursday afternoon
for southwest Oregon and most of Siskiyou County into southwest
Modoc County.

The axis of the trough will move to the coast Thursday night with
another shortwave trough likely to bring an increase in shower
activity and snow levels dipping to 3500 to 4000 feet msl. The
higher terrain may receive another inch or two of snow.

The upper trough will move inland Friday with a southwest flow aloft
veering to northwest. New shower activity will likely be most
numerous in the afternoon into the evening with both the timing of
the next shortwave and aid of day-time heating. Once again, snow
amounts will be minimal, mainly up to an inch, locally up to a
couple of inches with a snow level rising from 3500 feet to 5000
feet msl during the day.

Showers are expected to diminish Friday night into early Saturday
morning. There is some uncertainty in the duration/extent to which
showers and low to mid level clouds will linger on Saturday. With
the northerly flow, clouds and light showers will likely linger
longest from the coastal counties across Douglas County.

A warming and drying trend is expected during the weekend as a ridge
builds northeast into the region. Inland high temperatures on Sunday
are forecast to reach normal values for the first time in more than
two weeks, since April 8th. There are still about 10 to 15% of
ensemble members that indicate a sufficient amount of low level
moisture to ride over the top of the ridge that we have a slight
chance of light, drizzly showers for the Douglas County coast,
possibly extending to around Cape Arago in Coos County.

As time progresses from Monday through the end of Monday night,
there is a gradually increasing probability from around 10% to
around 30% that a cold front associated with the approaching trough
will spread a new round of rain to the southern Oregon coast. A
majority of ensemble solutions both delay any impact from the front
until after Monday night, and have the main impacts occurring north
of our area.

-DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 5 AM PDT Tuesday for ORZ029>031.
     High Wind Warning until 5 AM PDT Tuesday for ORZ031.
     Winter Weather Advisory until midnight PDT tonight above 5000
     feet in the for ORZ028.
     Winter Weather Advisory until midnight PDT tonight above 4500
     feet in the for ORZ027.

CA...Wind Advisory until 5 AM PDT Tuesday for CAZ084-085.

Pacific Coastal Waters...
     Gale Watch from late Tuesday night through Wednesday afternoon
     for PZZ350-356-370-376.
     Hazardous Seas Warning until 5 AM PDT Tuesday for
     PZZ350-356-370-376.