High Surf Advisory 6, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
337 AM PST Wed Feb 8 2017

.DISCUSSION...Water vapor and precipitable water vapor imagery show
a stream of tropically-sourced moisture heading towards Southern
Oregon and Northern California. Low pressure will deepen to the
north of this moisture, and the forecast area is in store for
moderate to strong winds and heavy precipitation later today into
Thursday.

The tropical connection of this moisture will push snow levels up
sharply today, and heavy rain upon snowpack means the potential for
flooding. In fact, the Pit River in Modoc County is already in
flood stage, and this will only worsen as temperatures increase
and rainfall arrives today, but moreso late Thursday when rainfall
could be heavy at times. A Flood Warning has been issued for
this.

High winds will impact areas from the coastal waters to the East
Side. Winds really start cranking tonight into Thursday morning. The
modeled south to north component of the coastal low level winds
ranks in the top 1 percent for this time of year, so we expect
significant impacts at the coast including the potential for tree
damage and power outages.  Further inland, 700mb southwesterly winds
peak near 80kt and this will be sufficient to bring high winds to
the Shasta Valley, the high Cascades and Siskiyous, and portions of
the East Side. High Wind Warnings and Wind Advisories have been
issued at NPWMFR. Winds will taper off in most places by late
Thursday. It must be noted that the ECMWF has a significantly weaker
low pressure center over the Pacific waters in its forecast for
Thursday morning, at 988mb compared to the 06Z GFS 979mb, so our
forecast does represent the worst case scenario between those two
models.

Returning to the hydrological concerns, Areal Flood Watches cover
most of the forecast area due to the potential for sharp rises in
rivers and streams as well as potential for landslides where the
highest rainfall rates are forecast. The operational GFS and GEFS
solutions are remarkably similar in terms of Integrated Vapor
Transport (IVT), and have been so for the past 2 model runs, keying
in on Thursday morning for off-the-charts IVT values and the
heaviest rainfall rates. This is the time period we're most
concerned for urban flooding at coastal towns, but heavy rain could
occur at other times during the Areal Flood Watch. Heavy rain will
also impact wildfire burn scars in Western Siskiyou County, and
we have issued a Flash Flood Watch for these areas.

In addition to areal flooding, a host of main stem river points
will near flood stage over the next few days, and Flood Watches
have been issued for the Coquille River at Coquille, South Fork
Coquille at Myrtle Point, Klamath River near Seiad Valley, Scott
River near Fort Jones, and Sprague River near Beatty.

A cold upper trough swings through Friday and drops temperatures
sharply, and will bring snow to areas above 3000 feet.  There is
still some uncertainty in timing and precipitation amounts with this
feature, so we don't have specifics in terms of winter travel
impacts at this time.

Please see the previous discussion below for more details on the
weather pattern after the high winds and heavy rain.

Thursday Night through Tuesday...While the bulk of the
precipitation is expected to move out of the area by Thursday
Night, the upper level trough and surface low will remain just
offshore of the Pacific Northwest, producing southwest flow and
numerous showers over our forecast area. the trough will slowly
slide east, and pass onshore Friday afternoon. The models have
some varying ideas about how this will manifest at the surface,
with the GFS producing gusty winds and moving a bit quicker, the
ECMWF slower with little to no significant winds, and the NAM
somewhere in between. No matter the timing or the winds, there
will be another round of moderate precipitation Friday morning,
followed by showers in the evening and overnight. Snow levels
should stay above 4000 feet, but some light snow may make it down
to around 2000 feet as snow levels drop Friday night. With the
heavy rains from the previous days, flooding concerns will likely
continue into the weekend.

Ridging and surface high pressure will build in quickly behind the
departing trough on Saturday, and trends suggest that these will
keep the forecast dry through the remainder of the forecast term.
This should help dry the area form the extensive rains of the short
term, and allow the river levels to drop. Also, with mostly clear
skies and easterly flow, temperatures could warm to 5 to 10 degrees
above normal for the weekend and into early next week. Highs around
60 will not be out of the question for the valleys of the West Side,
but extensive snowpack in the mountains and East Side may limit
warming there. -BPN

&&

.AVIATION...08/12Z TAF CYCLE...Areas of MVFR/IFR along the coast and
in the Umpqua Basin will clear to MVFR to VFR later this morning...
then areas of MVFR cigs/vsbys with higher terrain obscured will
develop late this afternoon into this evening as precipitation
becomes heavier. The lower conditions will persist through Wednesday
night. Over the remainder of the area...VFR conditions will prevail
initially...but areas of MVFR cigs with higher terrain obscured will
develop late this afternoon into this evening as precipitation
becomes heavier. The lower conditions will persist through Wednesday
night. Gusty winds will develop area wide which will lead to
turbulence inbound and outbound from the terminals. Low-level wind
shear is possible at KOTH, KRBG, KMFR, and KLMT after 18z
Wednesday.

&&

.MARINE...Updated 200 AM PST Wednesday 8 February 2017...Seas will
be steep this morning due to fresh south short period swell. A warm
front will move north through the area today. South winds will
increase to gale force, which will generate high seas. South storm
force winds will develop tonight into Thursday morning as a very
strong cold front moves through. Seas will become extremely
dangerous and mariners are urged to monitor the forecast for
updates. Weaker fronts will move onshore Thursday night and Friday
with seas remaining hazardous. High pressure will then build
offshore making for a relatively quiet weekend with moderate
northwest swell.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 1 PM this afternoon to 4 PM PST Thursday
     for ORZ030-031.
     Flood Watch from 11 AM PST this morning through Thursday evening
     for ORZ024>031.
     Wind Advisory from 1 PM this afternoon to 4 PM PST Thursday for
     ORZ030-031.
     High Wind Warning from 4 PM this afternoon to 1 PM PST Thursday
     for ORZ021-022.
     Flood Watch through Thursday afternoon for ORZ021>023.
     Wind Advisory from 10 PM this evening to 4 PM PST Thursday for
     ORZ023>025.
     High Wind Warning from 10 PM this evening to noon PST Thursday
     for ORZ027-028.
     Wind Advisory from 10 AM this morning to 10 AM PST Thursday for
     ORZ026-029.

CA...High Wind Warning from 1 PM this afternoon to 4 PM PST Thursday
     for CAZ085.
     Flood Watch from 11 AM PST this morning through Thursday evening
     for CAZ080>085.
     Wind Advisory from 1 PM this afternoon to 4 PM PST Thursday for
     CAZ085.
     Wind Advisory from 10 AM this morning to 10 AM PST Thursday for
     CAZ084.
     Flash Flood Watch from 10 AM PST this morning through Thursday
     afternoon for CAZ080.
     High Wind Warning from 10 AM this morning to 10 AM PST Thursday
     for CAZ081.
     High Wind Warning from 10 PM this evening to 4 PM PST Thursday
     for CAZ083.

Pacific Coastal Waters...Small Craft Advisory until 7 PM PST this evening for
     PZZ350-356-370-376.
     Storm Warning from 7 PM this evening to 7 AM PST Thursday for
     PZZ350-356-370-376.
     Gale Warning from 8 AM this morning to 7 AM PST Thursday for
     PZZ350-356-370-376.

NSK/BPN/JRS