Gale Watch 37, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
913 AM PST Thu Nov 23 2017

.DISCUSSION...An update to the forecast is not necessary this morning.
With the forecast for a rainy (mainly in southwest Oregon) and
windy (east of the Cascades) Thanksgiving, the focus for the
afternoon issuance will be the details of the next couple of
frontal systems late Saturday into early Monday. Model consistency
regarding the weekend forecast has been poor with first the ECMWF
and now the GFS indicating a stronger solution that is at odds
with a majority of the ensemble members. The main element of
potential impact is wind speeds. A period of strong south winds
is possible. As is normal for this time of day, we are still
awaiting key pieces of information that will come with the arrival
of the 12Z ECMWF data. There is also concern with how quickly snow
levels will drop Sunday night. The 12Z GFS has continued its trend
of slowing the arrival of the Sunday system. This continues to
support the forecast of snow levels dropping to pass levels late
Sunday night as precipitation is tapering off. It is also trending
toward slightly reduced snow amounts. We will wait for the
arrival remainder of the 12Z data before deciding on the need for
adjustments.

&&

.AVIATION...23/12Z TAF CYCLE...areas of MVFR cigs and local IFR cigs
near the coast will move inland this afternoon, mostly on the west
side north of the Umpqua divide and over most of the west side and
into the Klamath basin overnight. Low level wind shear will persist
through the early morning at all 4 terminals. -Sven

&&

.MARINE...Updated 300 AM PST Thursday 23 Nov 2017...Steep to very
steep seas will persist this morning, remain steep this afternoon
and evening, then ease below advisory levels overnight. South to
southwest winds will also ease during this time frame. Calmer
conditions are expected Friday through Friday night. Then, another
frontal system will bring strengthening south winds Saturday, with
gales possible and very steep seas Saturday night. Seas will remain
high and steep Sunday into early next week. -Spilde

&&

.PREV DISCUSSION... /Issued 452 AM PST Thu Nov 23 2017/

DISCUSSION...Yet another day of challenging high temperatures
with a combination of a cooler air mass moving in this afternoon
and already fairly warm temperatures over the region. All of the
ridge sites are warm and even Ashland is already at 63 degrees at
4 AM. Winds at a couple of thousand feet are near 30 kt and this
should mix a warmer air mass aloft, with 925 MB temps of 17C, down
before the cooler air mass moves in later today. Winds will be at
advisory strength, mostly in the higher elevations of the east
side with 700 MB winds around 50-55 kt. this front will continue
to bring significant, but not extreme rainfall to the region. With
the upper ridge pattern already transitioned to a zonal flow
pattern this front will bring precipitation across the east side
with the front dissipating over the east side into friday morning.

Friday will see a break in the action as an upper trough deepens
offshore ahead of the next system moving in Saturday, but with a
cooler air mass over the region with 700 MB winds from the west
leading up to the morning temperatures will be notably cooler than
today's.

This first of a one-two punch of systems this weekend moves in
Saturday on the left exit region of a 110 kt jet, but this mini
jet will move out of the region by late afternoon as the warm
front shifts to the north of the area. The timing of this system
has been delayed with the EC and the NAM, with the GFS being the
most aggressive and have shifted the timing back to match closer
to the EC. As the front, now showing to move in Sunday, approaches
the east side and higher elevations 700 MB winds are looking to be
very strong with most models showing in excess of 70 kt Sunday
morning.

Sunday looks to be wet throughout the day across the region, but
snow levels will remain high through the evening. However, by
Monday morning snow level still look to drop to pass levels in the
Cascades and Siskiyou Summit and possibly Black Butte Summit. This
will happen at the tail end of the front and snow amounts should
not be high as the bulk of the front and the heaviest
precipitation will have already moved through.

Showers look to taper off quickly on Monday. A stable air mass is
likely to produce areas of morning valley fog on Tuesday.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 10 PM PST this evening for ORZ030-031.

CA...Wind Advisory until 10 PM PST this evening for CAZ085.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas
     until 10 PM PST this evening for PZZ350-356-370-376.
     Hazardous Seas Warning until 10 AM PST this morning for
     PZZ350-370.

DW/JRS/SK