Small Craft Advisory 35, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
251 PM PDT Sat Apr 8 2017

.SHORT TERM...Scattered to numerous showers this afternoon. The
size of each individual shower is quite small. Radar returns look
like popcorn. Showers are due to weak instability and terrain
forcing. Showers will decrease after sunset as the airmass
stablizes. Water vapor satellite shows a relatively dry slot above
700 millibars moving over western Oregon at this time. This will
help to dissipate any high clouds and the stabilizing in the lower
levels will help to dissipate the lower clouds. This will all
combine to cause clearing skies overnight and, along with the
colder airmass, will allow temperatures to drop into the mid 20s
to mid 30s west of the Cascades and into the 20s with some
isolated upper teens east of the Cascades. With blooming fruit
trees on the west side, have issued a freeze warning for Jackson
and Josephine County valleys.

The next disturbance moves on shore late tomorrow afternoon and
through the forecast area overnight into Monday morning. This
system is another quick mover. Snow levels will remain at around
3000 feet.

After that, a short lived ridge moves in Monday night as the next
disturbance begins to deepen off the northern California coast.
Models continue to deepen it as it moves north-northeastward and
tracks west of the southern Oregon coast on Tuesday. Pressure
gradients increase and this system should produce strong south
winds in the coastal waters and in exposed areas in Coos and Curry
Counties on Tuesday.

.LONG TERM...Wednesday through Saturday Night...Wednesday opens with
a deep trough just offshore, and its associated surface low
deepening and sliding up the coast. Models agree in the pattern, but
differ in the timing by about 6 to 8 hours. Have sided with the GFS
solution more than the others, mainly due to the more detailed and
better resolved solution, but given the differences in the ensembles
and other model suites, suspect the timing of the winds,
precipitation, and other fields will change over the next few
cycles.

Despite the time that the front and low do move through, confidence
is high in the forecast for gusty winds and periods of heavier rain
Wednesday morning or afternoon, with showers continuing overnight
and into Thursday as the upper level trough slides by overhead.
Winds with this system could be strong, with forecast pressure
gradients similar to, but not as tight, as the wind storm from
Thursday and Friday of the previous week. It is too early to
consider Watches or Warnings, so will keep an eye on this in case
another high impact event begins to resolve itself. Fortunately,
snow levels should begin at about 6000 feet, only dropping to below
4000 feet once the front and the heavier precipitation passes, so
winter weather and hydro concerns are not pressing. Will update
the wind and rain forecast for this storm as necessary.

The pattern for the remainder of the forecast term beyond Thursday
is very uncertain due to vast differences in the various model
suites and their ensembles, which appear to arise form differences
in how each model handles a high amplitude ridge over the northern
Pacific and the Bering Sea. There may be a day or two break with
high pressure in control before the next system arrives by the
weekend, or systems could be line up one after another. Have left a
chance for precipitation in during just about every period, with
higher chances in the periods more likely to have a frontal passage.
With such high spread in the models, uncertainty remains way too
high to make any skillful detailed forecast going into next
weekend. -BPN

&&

.AVIATION...08/18Z TAF CYCLE...Expect mainly VFR today across the
forecast area, although periods of MVFR are possible along the coast
and within any scattered showers through the early afternoon. Clouds
will increase once again late this evening and tonight as the next
front approaches the region. Winds will become gusty along the coast
by morning, but most other areas should not see stronger winds until
beyond the current TAF period. -BPN

&&

.MARINE...Updated 230 PM PDT Saturday 8 April 2017...Steep seas
will persist into this evening while a weak high moves inland. The
next front will follow close behind. Winds and seas increase again
late tonight with gales developing early Sunday. The front will move
onshore early Sunday evening. The gales will be strongest beyond 5
nm from shore and near Cape Blanco. High pressure will briefly build
over the coastal waters Monday...though with west swell dominated
seas likely remaining high and steep. The high will weaken Monday
night with a very brief improvement of conditions into Tuesday. A
strong front is likely to approach the waters from the southwest
late Tuesday and good bring another episode of gales Tuesday night
into Wednesday. Model agreement is very good into early Tuesday
then diminishes further beyond Wednesday. -DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Gale Warning from 11 AM to 8 PM PDT Sunday for ORZ021.
     Freeze Warning from midnight tonight to 9 AM PDT Sunday for
     ORZ024-026.

CA...None.

Pacific Coastal Waters...Gale Warning from 11 AM to 8 PM PDT Sunday
     for PZZ350-356-370-376.
     Small Craft Advisory from 2 AM to 8 PM PDT Sunday for
     PZZ350-356-376.
     Small Craft Advisory for hazardous seas until 8 PM PDT this
     evening for PZZ350-356-370-376.
     Small Craft Advisory from 2 AM to 11 AM PDT Sunday for PZZ370.

KRS/BPN/DW