Small Craft Advisory 18, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
353 AM PST Sun Mar 5 2017

.DISCUSSION...Showers continue across the area this morning, with
snow levels dropping to around 1000 feet, or even lower in some
places. Offshore, a compact surface low, the reflection of a
shortwave aloft, is currently beginning to make its way onshore.
This feature will bring a burst of precipitation to the area as it
moves through this morning, and may also produce some isolated
lightning strikes.

As the day passes, the upper level trough will make its way
onshore and produce significant instability over Southern Oregon
and Northern California. Showers will continue through the day and
into the afternoon, before a second wave pushes into the region
tonight. This second wave will bring enhanced dynamics, and should
act to produce even more numerous showers, some of which could
produce periods of heavy precipitation. Meanwhile, snow levels
will remain low, at 500 to 1000 feet, so those showers could take
the form of heavy snow for much of the area, especially over
higher terrain, where orographics are strongest and snow-to-
water ratios are higher. A winter weather advisory remains in
place through Monday to account for this near continuous snowfall
event, and for the prospect of blowing snow east of the Cascades
on Monday. Some of the higher terrain west of the Cascades has
been upgraded to a Winter Storm Warning for impacts of heavy
snowfall to area roads tonight into Monday as well. For detail on
these, see the Winter Weather Message at PDXWSWMFR.

Conditions will improve late Monday, but showers will never
really come to an end before the next system arrives Tuesday
morning and afternoon. Models continue to show the development of
a surface low just offshore, the offspring of a front stretching
all the way up the coast of the Pacific Northwest. Snow levels
will rise to near 5000 feet as the low approaches. The front and
low are then expected to produce gusty winds along the coast and
moderate to heavy rain inland before dissipating and sliding to
the north by Tuesday night.

The pattern will remain wet and unsettled for the duration of the
forecast period, but confidence in any specific feature beyond
Tuesday remains uncertain. Models have shown little consistency
during this time, but are continuing to produce various systems
through the rest of the week. Fortunately enough, the models are
also trending warm beyond Tuesday, with temperatures warming to
more normal values for this time of year, and snow levels
remaining well above all but the very highest passes. However, if
past model behavior is any indication, it would not be surprising
for the models to trend cooler over the next several forecast
cycles. We shall have to wait and see. -BPN

&&

.AVIATION...05/06Z TAF CYCLE...Expect a mix of VFR and MVFR
conditions in rain and snow showers at local west side terminals
tonight. A cold front is moving through this evening, and snow
levels will lower to 1000 feet overnight and locally down to 500
feet in heavier showers. A band of moderate precipitation is now
moving into the Cascades and will likely bring snow to east side
locations overnight with IFR conditions possible. Showers will
decrease in coverage from west to east tonight, but another
disturbance will bring increased snow showers to the west side by
dawn with MVFR to IFR conditions. -Wright

&&

.MARINE...Updated 400 PM PST Saturday 4 March 2017...Moderate to
gusty southwest winds and steep seas will persist over the waters
tonight into Sunday morning. Wind gusts to gale force are expected
over the outer waters north of Cape Blanco late Sunday morning
through Sunday afternoon with steep to very steep seas around 15 ft
at 12 seconds for all areas north of Cape Blanco. We have issued
gale/hazardous seas warnings for PZZ370 (North Outer) with a
hazardous seas warning for PZZ350 (North Inner). Small craft
advisories are in effect elsewhere. Gusty winds and steep seas will
continue Sunday night through Monday. Then, models are showing yet
another stronger front moving into the waters on Tuesday with the
potential for gales and very steep seas. A watch may be necessary
tonight or tomorrow. Additional disturbances will bring periods of
moderate or higher winds with steep to very steep seas through the
week. -Spilde

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 PM PST Monday for ORZ029>031.
     Winter Weather Advisory until 4 PM PST Monday for ORZ027-028.
     Winter Weather Advisory until 4 PM PST Monday ABOVE 1500 FEET
     for for ORZ021>026.
     Winter Storm Warning from 4 PM this afternoon to 4 PM PST Monday
     ABOVE 2500 FEET for for ORZ024>026.

CA...Winter Weather Advisory until 4 PM PST Monday for CAZ080>083.
     Winter Storm Warning from 4 PM this afternoon to 4 PM PST Monday
     for CAZ080-082-083.
     Winter Weather Advisory until 4 PM PST Monday for CAZ084-085.

Pacific Coastal Waters...Small Craft Advisory until 10 AM PST this morning for
     PZZ350-356-370-376.
     Small Craft Advisory from 7 PM this evening to 4 AM PST Tuesday
     for PZZ350-356-370-376.
     Hazardous Seas Warning from 10 AM this morning to 7 PM PST this
     evening for PZZ350-356-370-376.
     Gale Warning from 10 AM this morning to 4 PM PST this afternoon
     for PZZ370.

BPN/MS/TRW