Hazardous Seas Warning 31, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
1038 PM PDT Sat Apr 15 2017

Updated AVIATION Section

.DISCUSSION...No updates are necessary this evening. High pressure
is bringing dry weather with just some high clouds streaming in
from the southwest. The high clouds will become thicker with time
overnight, so we're not expecting it to get as cold as it did last
night. The high clouds are the harbinger for the next storm
system, which is currently spinning out near 39 North and 137 West
or about 675 miles off Cape Mendocino. There is a chance of some
rain across SW sections of the CWA Easter Sunday morning, then
rain chances increase with rain becoming likely over most of the
area in the afternoon/evening. The pressure gradient from MFR-RDD
Sunday afternoon is not too shabby (-5 to -7 mb), which, if winds
aloft were a bit stronger, might cause advisory level southerly
winds in parts of the area. But, model 700 mb winds are only in
the 35-45 kt range, so while it will get breezy to windy at times
in the Shasta Valley, portions of the Rogue Valley and over the
East Side, winds should remain sub-advisory (gusts to 45 mph)
strength. Models have been hinting at some instability along the
coast and west of the Cascades in the afternoon/evening as the
upper cold pool aloft moves overhead. While the probability of
thunder is still relatively low, we wouldn't be surprised if there
were a clap or two of thunder. The entire system moves inland
Sunday night, but we'll remain in a rather moist, southwest flow
aloft with additional upper disturbances arriving from the
Pacific. So, an unsettled pattern will continue into the new work
week. -Spilde

&&

.AVIATION...16/06Z TAF CYCLE...VFR conditions are expected to
prevail through Sunday morning. Sunday afternoon guidance indicates
a lot of low level turbulence in and near the valleys across the
area and conditions favorable for more mountain wave turbulence
under southwest flow. Southeast winds may reverse in some of the
valleys to the lee of the terrain. Rain is expected to develop
during the afternoon and evening with MVFR developing along and near
the coast and in Northern California around 17/00Z. -BTL/Spilde

&&

.MARINE...Updated 245 pm PDT Saturday, 15 April 2017...
High pressure centered along the Washington coast this afternoon and
low pressure inland near the Oregon and California border will cause
north winds to briefly increase through this evening. This will
result in an area of hazardous seas into this evening. Late tonight
through Sunday winds will become southerly and increase as a frontal
system arrives from the SOUTHWEST. Rain will move in through the day
and conditions will become hazardous to small craft beginning Sunday
afternoon and evening. Low pressure will then remain west of the
area into Tuesday bringing breezy south winds, periods of rain, and
steep seas. A stronger frontal system is expected ON Wednesday. BTL

&&

.PREV DISCUSSION... /Issued 609 PM PDT Sat Apr 15 2017/

SHORT TERM...The low cloud has all cleared out and high cloud is
thin enough that it's turned out to be a rather sunny day across
the area today. Under full April sun, temperatures are probably
going to top out right around normal for most of us today. This
is the result of a weak and transient upper ridge that is building
over the PacNW today.

The nice weather will be short-lived, however, as the next frontal
system is taking shape between 130W and 140W right now. This
system will move in tomorrow and bring light to moderate rain to
much of our forecast area. As this system moves away Sunday night
into Monday, we will be left with moist, southwest flow in its
wake, and this will keep rain chances in place for most of us with
the focus being in the upslope areas of the coastal mountains.
Another frontal system will arrive in the southwest flow and
increase rain coverage and intensity later Monday into Monday
night, especially in those upslope areas in the coastal mountains
again. None of these systems look particular impressive, so we
don't see a need for any watches, warnings, or advisories at this
time. It is possible that one of these fronts kick out some
advisory-worthy snow in the mountains or wind in the usual spots,
but nothing is indicated at this time. -Wright

LONG TERM...Extended discussion, Wednesday through Saturday.
Models are in good agreement Wednesday, shifting an upper level
ridge east and bringing another front into the region. On Wednesday
the system comes in with the right entrance region of a southerly 80
kt jet, and the energy stays focused on northern California as the
left exit region of a 120 kt jet moves into the region. The jet axis
moves east Thursday with an upper level ridge building in behind it
by Thursday evening with a weak thermal trough deepening on the
coast and offshore flow spreading across the east side by Friday
morning. However, this break in the precipitation is short lived as
the upper ridge shifts east and a weak front washes out Saturday as
it collides with the ridge, resulting in light showers over the west
side, mostly at the coast. Sven

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory from 8 PM Sunday to noon
     PDT Tuesday for PZZ350-356-370.
     Small Craft Advisory for hazardous seas until 11 PM PDT this
     evening for PZZ350-356-370-376.
     Small Craft Advisory from 2 PM Sunday to noon PDT Tuesday for
     PZZ376.

MAS/TRW/SBN/BTL