Gale Watch 7, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
852 AM PST Mon Mar 5 2018

.UPDATE...A weak ridge will bring clear, quiet weather today and
tomorrow, and much of Wednesday. Made some updates to
temperatures... lows were cold this morning, but clear skies will
support good mixing, bringing temperatures to the upper 50s in
west side valleys, and upper 40s east of the Cascades. Tonight
will be another cold night, with some patchy valley fog west of
the Cascades... though drying lower level conditions should
support less fog formation than this morning. Tuesday afternoon
will be a few degrees warmer than today. The next wet windy system
will approach the coast late Wednesday. The focus today will be on
refining the details of that system... no updates have been made
to the previous forecast to that time period, so see previous
discussion for more information. -MSC

&&

.PREV DISCUSSION... /Issued 433 AM PST Mon Mar 5 2018/

SHORT TERM...A weak upper level ridge is building into the area
today. This is bringing dry and stable conditions to the area. Morning
fog is expected to develop in many valleys west of the Cascades,
with clearing in the late morning. This pattern remains in place
into Tuesday as the ridge remains over the area. Offshore a strong
low pressure system will approach the region from the west late
Tuesday and Tuesday night. A warm front is expected to move into
western portions of the area on Wednesday and bring a chance for
precipitation, mainly to the coast. A strong cold front will
approach on Wednesday, reaching the coast by early Wednesday
evening. A second stronger frontal system will then move towards
the coast Wednesday night and then gradually inland on Thursday.

Ahead of the strong front on Wednesday, expect gusty south to
southeast winds to develop across portions of the area as a
strong mid level jet moves inland and the surface pressure
gradient increases. Models support the potential for strong gusty
winds to develop in the Shasta Valley late Wednesday afternoon
into Wednesday evening and across portions of the east side
Wednesday evening, inoculating at Summer Lake and over the
mountains in Lake, eastern Klamath and Modoc counties. Advisory
level winds with gusts of 40 to 45 mph are possible in the
southern Shasta Valley and Summer Lake areas Wednesday evening and
night. There remains variability though on the timing and
strength of these winds though with the GFS showing a stronger mid
level jet moving into the area versus the NAM, SREF and ECMWF. So
will continue to monitor this with future model runs.

Areas of light to moderate precipitation are expected to spread
inland late Wednesday afternoon and Wednesday evening. Snow levels
are expected around 4500 to 5500 feet elevation as precipitation
spread inland. Models then indicate this front will move east of
the Cascades Wednesday night. A second low and frontal system
will approach the central Oregon coast Wednesday night. This low
is forecast to move north-northeast along the Oregon coast with
the associated cold front extending south and gradually moving
inland Thursday into Thursday night.

A second round of eve stronger winds is possible with this strong
front on Thursday. Gusty winds are likely for most locations.
Models show relatively good agreement with a 45 to 65 kt 700 mb
jet moving into the area Thursday morning into Thursday afternoon,
which combined with a strengthening surface pressure gradient
will bring gusty winds to much of the area. Strongest winds are
expected for areas east of the Cascades, especially in the Summer
Lake area and over the mountains in Lake, eastern Klamath and
Modoc counties. The GFS and NAM support the potential for warning
level winds gusting to 60 mph or more in the Summer Lake area and
across eastern mountains on Thursday. So, will need to monitor
this with future model runs. In the Shasta Valley, also expect
strong gusty winds with model forecasts indicating the potential
for advisory level winds on Thursday. Although not as strong, also
expect gusty winds in the Rogue Valley from Medford to Ashland.
Along the coast, a 50 to 65 kt lower level jet is forecast to move
onshore Thursday morning and early Thursday afternoon resulting
in gusty winds for many coastal locations and strong winds
possible over the coastal headlands.

Areas of moderate to light precipitation will move into the CWA
Thursday. Snow levels are expected to be around 4500 to 5500 feet
through Thursday evening as this front moves inland. Periods of snow
are possible over some higher passes in the Cascades Thursday
morning into Thursday night, but amounts are expected to be
mainly light. Note, downslope effects from winds may delay the
onset of precipitation for portions of the Rogue Valley and the
Shasta Valley on Thursday morning with increasing chances for
precipitation Thursday afternoon and evening as the front
gradually pushes inland.

AVIATION...05/12Z TAF CYCLE...Skies are main clear with some
areas of western valley fog/low clouds. Fog will be a concern for
western valleys this morning. Areas of fog are expected in the
Coquille, Umpqua and Illinois valleys, including at KRBG, as well
as in the Grants Pass area. Conditions are marginal for fog to
develop in the Rogue Valley near KMFR though. Given the clear
skies and lingering moisture in the boundary layer, have kept MVFR
visibilities in at KMFR for this morning beginning around
sunrise. Conditions are expected to improve to VFR late this
morning area wide. Local MVFR/IFR may redevelop in western valleys
again early Tuesday morning around 12z.

-CC

MARINE...Updated 200 AM PST Monday 05 Mar 2018...Weak high pressure
will persist near or over the waters through Tuesday. This will
result in light to moderate winds and seas between 7 and 8 feet.

The next time period of concern start on Wednesday. A front will
approach the waters with south winds increasing over the waters late
Wednesday afternoon. Moderate to strong south winds will continue
through Thursday morning. Right now there is good agreement winds
will be strongest Thursday morning with gales possible mainly beyond
10 nm from shore.

Winds will gradually decrease Thursday afternoon, then more so
Thursday night. However seas will remain high through Thursday night
as we transition from wind generated waves to a fresh southwest
swell. Calmer conditions return Friday and continue through
Saturday. -Petrucelli

PREV LONG TERM DISCUSSION... /Issued 219 PM PST Sun Mar 4 2018/

LONG TERM...Thursday March 8 through Sunday March 11...While there
was a brief period of inconsistency in last night's model runs
regarding timing of a frontal system late this week, 12Z model runs
are now back in lock step. As a result, we still have moderate to
high confidence in the extended forecast at this time.

A wet and windy frontal system will move through our area on
Thursday. We will see heavy rain at the coast and in the coastal
mountains with less amounts inland, as usual. Snow levels are
expected to rise to around 5000 feet, so snow impacts should occur
above all the passes on I-5. Winds are probably the bigger impact
from this storm, and Thursday's winds have been increased again for
the usual wind-prone areas...Shasta Valley and East Side. At this
time, it looks like at least advisory level winds, but some areas
may reach warning criteria if current guidance holds.

On Friday, the front moves east of us, but the upper trough will
move through with plenty of showers and snow levels lowering back
down to around 3000 feet. Despite lowering snow levels, snow impacts
are expected to be minimal as the heaviest of the precipitation will
be gone by then.

Model guidance remains in unusually good agreement even into next
weekend. A very moist frontal system will approach the west coast on
Saturday. We may see a batch of showers on Saturday as a weak upper
disturbance moves through. The main frontal band, which looks very
wet, incidentally, will then edge in toward the coast Sunday. Being
day 7, confidence in this timing isn't that great, but both the GFS
and Euro (and their ensembles) show the bulk of the rain holding off
until Sunday evening or night. -Wright

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Dense Fog Advisory until 9 AM PST this morning for ORZ023.

CA...None.

Pacific Coastal Waters...None.

MSC/CC/MAP