Gale Warning 28, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
221 PM PST Sun Dec 25 2022

.DISCUSSION...25/12Z NAM/GFS/EC in.

The current northern hemispheric pattern continues to show a
progressive wave number of five around the globe, with a notably
high amplitude and very cold trough over eastern Canada and the
northeast US. Over the next several days, the progressive five
wave pattern will persist, but the amplitude of the troughs will
diminish, supporting a warmer weather regime in the mid-
latitudes, at least over the northwestern semi-hemisphere.

Meanwhile, a long wave ridge is now over the west coast states,
and the ridge axis broke to the east of the area today. Flow
aloft has become southwesterly ahead of the next system. A warm
front has already lifted north of the Medford forecast area, and
snow levels are up around 9500 feet.

The pattern will remain quite progressive. The next short wave
will push another front onshore Monday morning. The main concern
with the Monday system is wind, and the coastal waters will likely
see gale force winds. Over the land areas, expect gusty winds
over the ridges, east of the Cascades, and in the Shasta Valley.
At this time, it does not appear that High Wind Warnings or Wind
Advisories will be necessary for this system.

However, that will not be the case with the next front, which will
be getting plenty of upper level support, as it will be associated
with a long wave trough. The trough will move onshore Tuesday
evening, and the surface front will move onshore ahead of it late
Monday night into Tuesday morning. Once again, snow levels will
be up around 9000 feet ahead of the front. This front will likely
bring storm force winds to the coastal waters, along with high
winds to the coast, ridges, Shasta Valley, and east side. High
Wind Warnings have been issued for these areas.

Snow levels will finally go down behind this front, but it still
will not be particularly cold, dropping down to 4000 to 5000 feet
Tuesday afternoon and to 3500 to 4000 feet Tuesday night. Snow
will become a concern at that time, but precipitation will also be
diminishing Tuesday night.

Several warm systems in succession does raise the possibility of
flooding due to precipitation mixing with snowmelt. Historically,
the biggest flooding events in this area occur in this kind of
pattern. At this time, due to low antecedent streamflows and a
relatively moderate early season snowpack, flooding is not
anticipated. However, streams in the Coquille basin are forecast
to rise near action levels beginning Tuesday night. This situation
will be monitored closely over the coming days.

Extended Discussion...Wednesday 28 Dec 2022 through Sunday 01 Jan
2023.

Our long term weather picture has some pieces that are consistent
from yesterday's data, some that have come into higher confidence,
and (as usual) still some aspects that still have important model to
model differences.

It is consistent that our area will have active weather through the
long term with short breaks between systems, and a few systems, none
of which individually will attain the strength/impact of the major
system in the short term period. Wind and snow headlines are more
likely to be of an Advisory rather than a Warning impact level. Any
risk of hydrologic/flooding concerns during the long term looks to
be minimal at most, and temperatures should not stray too far from
normal levels.

It is also consistent that the long term period looks to begin with
the lowest snow levels of the long term period. A shortwave trough
has a high probability of generating light showers and snow showers
Wednesday morning with snow levels around 3000 to 3500 feet, perhaps
as low as 2500 feet in southwest Oregon. Morning snow showers of up
to an inch are possible, except up to a couple of inches around
Crater Lake.

There is higher confidence in the big picture evolution of the
weather pattern. Shower activity is likely to diminish but not end
altogether Wednesday afternoon (into the evening for the area inland
from our coastal counties).

The next wet frontal system is expected Wednesday night into
Thursday morning with snow levels around 3500 to 4000 feet.
Diminishing shower activity later Thursday will be followed by
another similar/slightly stronger front Thursday night into Friday.
Post frontal shower activity is likely to have a diminishing trend
Friday afternoon into Friday evening.

In the 60 hours from Wednesday morning through Friday afternoon,
1.50 to 4.00 inches of precipitation are forecast for the coast
(highest for Curry County), around 1.00 to 2.50 inches from the
Coast range to the Cascades (highest for the mountains), and 0.50 to
1.50 inches for the east side (highest for northern Klamath County
and southeast Siskiyou County).

There remain important model differences regarding the track (and to
a lesser extent the strength and timing) of what will be the
strongest system of the long term. It is increasingly looking like
the bulk of precipitation will occur south of our area Friday night
into Saturday night. Nearly every ensemble member has either
maintained or trended toward a track that has the center of the
system aimed south of our area. Snow levels will also be affected by
the track of this storm but they are forecast to be around 3500 to
4500 feet with the full suite of ensemble data showing about a 60%
probability that the northern portion of the moderate to heavy
precipitation certain to be associated with the storm will occur in
Siskiyou and Modoc counties (with the highest probability for
western and southern Siskiyou County, including the Mt. Shasta
region). In southern Oregon, there is a chance of light
precipitation.

During Saturday night into Sunday, a break between systems is
likely. A few ensemble members begin Saturday night with lingering
wrap around showers into the east side from the preceding trough.
But, the large majority of ensemble members show ridging, with about
half of those indicating sufficient low level moisture for very
light overrunning drizzly showers/snow showers. In any case, the
ridging would likely bring widespread valley low clouds and fog
Saturday night into Sunday...on New Year's Eve into New Year's Day.

The long term period ends with above normal model agreement that the
next large scale, moderately strong cold front will reach the west
coast during Sunday night with precipitation possibly spreading
inland before the end of Sunday night, but likely during Day
8/Monday.

&&

.AVIATION...25/18Z TAFs...Expect widespread coastal and
valley IFR/LIFR in low clouds and fog to continue this morning.
Areas of low clouds should linger into the afternoon, but general
improvement to VFR seems reasonable as models anticipate some drier
air to mixing into the boundary layer. Low level wind shear could be
an issue again along the coast beginning this evening and in many
valleys west of the Cascades by Monday morning. Areas of valley
LIFR/IFR will return this evening, then conditions Monday morning
will be more of a mix of categories as a front brings rain to the
coast late tonight, gradually spreading to the Cascades with areas
of terrain obscuration during Monday morning. -DW

&&

.MARINE...Updated 200 PM PST Sunday 25 December 2022...South winds
will increase tonight with gale force winds expected in the northern
waters and close to gales everywhere else as another front moves
through the waters. Hazardous seas will continue on Monday after
the frontal passage even though winds will subside below gale
force.

Monday afternoon into Tuesday, a very strong low pressure center
will develop closer to our region and track toward Vancouver Island.
Dangerous marine conditions are expected to develop during this time
with high end gales expected and a strong potential for winds to
reach storm force particularly late Monday night into early Tuesday
morning. Very high and steep seas are expected due to a mix of a
long period west swell and very high and steep south wind waves.
Models are still showing peak significant wave heights nearing 30
feet north of Cape Blanco on Tuesday. A storm warning will be issued
for headlands extending approximately 25 nm offshore for Monday
night. These wave heights will result in dangerous surf conditions
along the Oregon coast beginning Monday morning and continuing into
Wednesday morning. The maximum high surf is likely to occur Tuesday
afternoon.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 10 PM Monday to 10 AM PST Wednesday for
        ORZ029>031.

     High Wind Warning from 10 PM Monday to 10 AM PST Wednesday for
        ORZ030-031.

     High Wind Warning from 10 PM Monday to 10 AM PST Tuesday for
        ORZ021-022.

     High Surf Warning from 4 AM Tuesday to 4 AM PST Wednesday for
        ORZ021-022.

     High Wind Warning from 10 PM Monday to 10 PM PST Tuesday for
        ORZ027-028.

CA...High Wind Warning from 10 PM Monday to 4 PM PST Tuesday for
        CAZ081.

     Wind Advisory from 10 PM Monday to 10 AM PST Wednesday for
        CAZ084-085.

     High Wind Warning from 10 PM Monday to 10 AM PST Wednesday for
        CAZ085.

PACIFIC COASTAL WATERS...High Wind Warning from 10 PM Monday to 10 AM
        PST Tuesday for PZZ356.

     Small Craft Advisory until 10 PM PST Monday for PZZ356.

     Hazardous Seas Warning from 7 AM to 4 PM PST Monday for PZZ350-
        356-370-376.

     Storm Warning from 10 PM Monday to 4 AM PST Tuesday for PZZ350-
        356-370-376.

     Hazardous Seas Watch from Tuesday afternoon through late Tuesday
        night for PZZ350-356-370-376.

     Small Craft Advisory until 7 AM PST Monday for PZZ350-370-376.

     Small Craft Advisory from 4 PM to 10 PM PST Monday for PZZ350-
        370-376.

     Gale Warning from 10 PM this evening to 7 AM PST Monday for
        PZZ350-370.

     Gale Warning from 4 PM Monday to 4 PM PST Tuesday for PZZ350-356-
        370-376.

&&

15/16/07