Flood in Oregon, January 15 to 17, 2023

Area Forecast Discussion
National Weather Service Medford OR
448 PM PST Sun Jan 15 2023

.UPDATE...Updated the aviation discussion.

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.AVIATION...16/00Z TAFs...Conditions early this evening are mainly
VFR, though with lingering scattered showers and snow showers, areas
of mountain obscuration, and MVFR.

Late tonight into Monday, the atmosphere generally remains unstable
with mainly VFR. But, the air mass will stabilize a bit toward
morning. Where skies clear, areas of valley LIFR/IFR fog may form.
This is most likely in Douglas and Josephine counties, including
Roseburg and Grants Pass. But, is also expected towards 12Z in
Jackson County, including Medford. Valley conditions will slowly
improve during Monday morning into Monday afternoon, with
improvement to VFR expected. -DW

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.PREV DISCUSSION... /Issued 242 PM PST Sun Jan 15 2023/

SHORT TERM...

Showers remain on the radar this afternoon as a low remains within
our region. Some locations will continue to see minor snow
accumulations around 4000 feet, although the snow and rain will
really diminish into the evening and overnight hours. The sky is a
little more clear than models have also expected this afternoon
and this has lead to slightly warmer temperatures under the sun.
Still a few degrees cooler than yesterday, yet not by much.

As for tonight, the main weather hazard will likely be fog within
the valleys. Dewpoints during peak mixing are in the lower 30s
within Medford, although they're about 7 degrees higher around
the Grants Pass area. In any case, partial clearing tonight will
allow fog to form in the Illinois Valley around Grants Pass,
although the Medford area is a little more questionable as the air
is drier here. East of the Cascades fog also remains possible in
sections of the Klamath Valley. Some upper level energy will keep
the low chance of showers going tonight, although those chances
are fairly low as the air is indeed drying out.

Heading into Monday, the weather will remain in the lull, which
may be a welcome break to some. There is upper level energy
swirling around in the atmosphere with a little bit of moisture,
so scattered cloud cover seems reasonable for most of the day.
however, precipitation should be pretty low. The coast is the only
place we have precipitation in the forecast with a 20 to 30
percent chance of rain.

Monday night will be another period to watch out for fog. Models
anticipate a surface high building right over our region. It's not
a classic dense fog event as there appears to be some lingering
instability in the area. In addition, there is some moisture in
the middle of the atmosphere to provide mid level cloud cover.
Again, the coast will have a low potential for rain with the
probability of precipitation around 20 to 30 percent.

By Tuesday, an upper level short wave will bring a low chance of
rain to the coast and sections of the Umpqua Basin. There
probability of precipitation rises to 30 to 40 percent. A warm
front is also anticipated to push into the forecast area late on
Tuesday, so that will also contribute to the precipitation chances
throughout the day. The highest precipitation chances remain west
of the Cascades will lower chances east of the Cascades.

-Smith

LONG TERM... Wednesday and beyond

We'll see an overall transition in the weather pattern during the
extended period. Over recent weeks, we've been under this persistent
south to southwest flow with strengthening surface low pressure
systems developing along the coast. As you may have noticed, this
pattern favors strong south to southeast winds which leads to
enhanced precipitation along the Curry Coast, Siskiyou County and
Shasta Valley. At the same time, we've seen ample downsloping on the
Oregon side of the OR/CA border, especially for areas east of the
Illinois Valley. The cold front expected on Wednesday will move in
on northwest flow, and this pattern favors lower snow levels with
much less downsloping affects. As such, precipitation will be more
widespread across southern Oregon and more limited in our northern
California locations. This front isn't particularly strong, but will
be more typical for this time of year. Snow levels will be around
3500 ft, so there could be some wintry impacts at lower elevations
compared to recent weeks with greatest impacts expected above 4000
ft. Even still, the current forecast only indicates around 2 to 4
inches for Siskiyou Summit and the Mt Shasta City area, while the
Cascades could see advisory amounts. Winds will increase with this
front, but guidance for the windiest locations doesn't even reach
advisory criteria, so no wind headlines are anticipated at this
time.

Thursday will be a transition day with dry conditions for most areas
and some showers lingering along the Cascades. Showers will come to
an end by Thursday afternoon/evening as upper level ridging
strengthens over the eastern Pacific and nudges into the Pacific
Northwest. This will push the storm track well north of the area and
bring an extended break in the active weather. A shortwave could
ride over the top of the ridge on Saturday and glance by the
northern portion of the forecast area late Saturday into Sunday, but
this is much too far out to have confidence in any details.
Confidence is higher, however, for upper level ridging to dominate
the weather late this week, through the weekend and likely into the
following week. /BR-y

MARINE...Updated 200 PM PST Sunday, January 15th 2023...
Southwesterly winds will continue to decline through the afternoon,
with the strongest gusts possible north of Cape Arago. Even so, seas
will remain very steep and chaotic through this evening.

Seas are likely to remain steep but will continue to diminish later
tonight through Monday. Within ten nautical miles of the coast,
there will be a brief lull Monday evening through Tuesday.
Meanwhile, west swell-driven seas will build Monday evening in the
outer waters, creating hazardous conditions for small craft at least
through Tuesday afternoon. The next front will arrive late Tuesday
into Wednesday with another round of gales possible Wednesday
morning into the afternoon, with steep seas continuing through at
least Friday. -Price

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.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...None.

PACIFIC COASTAL WATERS...Hazardous Seas Warning until 10 PM PST this
     evening for PZZ350-356-370-376.

     Small Craft Advisory from 10 PM this evening to 10 AM PST Monday
     for PZZ350-356.

     Small Craft Advisory from 10 PM this evening to 4 PM PST Tuesday
     for PZZ370-376.

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