Freeze Warning 5, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
957 AM PST Thu Feb 23 2017

.Updated Aviation Discussion.

.UPDATE...Current observations show tapering showers over some of
the higher terrain areas, and that many areas reached below
freezing. As of the writing of this discussion, the coast is
hovering just above freezing. With skies over the coast currently
sunny--per reports from the public and visible satellite,
temperatures will warm today. The big question for the coast
tonight will be whether or not we will see enough cloud cover to
preclude freezing conditions ahead of the incoming system.

The other big challenge for today is the system coming in on
Friday and Friday night. The previous shift has done well to pare
down the watch issued yesterday (which was liberally applied in
order to note the potential for incoming weather). The goal today
will be to determine which areas will see advisory level snows
versus warning level snow amounts.

Additionally, will need to take a closer look at the Sunday storm
system as this could create additional issues this weekend. The
previous shift did a great job noting the possibilities with these
storms, so have included the previous discussion to give more
information in the meantime. -Schaaf

.AVIATION...23/18z TAF CYCLE...VFR conditions are expected to be
the predominate condition for the next 24 hours. The exception will
be at Roseburg where MVFR cigs will continue through the morning
hours. The TAF at Roseburg shows conditions improving at 21z, but
there's a chance it could improve earlier. Despite VFR conditions,
could not rule out partial mountain obscurations through at least
21z. -Petrucelli

&&

.PREV DISCUSSION... /Issued 427 AM PST Thu Feb 23 2017/

DISCUSSION...
Below freezing temperatures across much of the forecast area this
morning mean that black ice is possible on untreated roadways
today until road surface temperatures warm to above freezing.
Portions of the East Side and the mountains will remain below
freezing today.

Snow showers have dissipated overnight to just some lingering snow
flurries, mainly across the higher mountains and East Side. While
some showers are expected today these will be only isolated to
scattered in areas where they do occur and much lighter than
yesterday's. Additional accumulations will be an inch or less,
except along Winter Rim and the Warner Mountains, where 1 to 3
inches will be possible. Snow levels will rise to the 1000 to 2000
foot range this afternoon and evening.

Friday into Saturday another cold upper level low will move
southward along the coast. This low is not as strong as the one
that moved through yesterday, and the bulk of the precipitation
associated with it remains along and near the coast. With the
surface low centered offshore, low level flow across the interior
West Side will be southeasterly, which is not favorable for
substantial precipitation. Still, the Coastal Mountains of Coos,
Curry, and Siskiyou counties could see significant snow
accumulations above 1500 feet. In Josephine County there remains
significant concern for substantial snowfall in the Illinois
Valley down to about 1000 feet and on the Sexton passes. For
these areas winter storm watches remain in effect. For other
locations that were in a watch, we've cancelled the watch. Some of
these areas could still see lighter advisory type snow amounts,
in the 1 to 3 inch range in the valleys and 2 to 6 inches in the
mountains and Mount Shasta area. Snow levels with this one have
been adjusted based on relative 850mb, 700mb, and 500mb
temperature values based on rough verification from the frontal
system that just moved through. Thus, portions of the Rogue Valley
could see some snow, but amounts should be mostly an inch or less
below 3000 foot elevations.

Yet another low pressure system is expected to move in from the
north-northwest Sunday through Tuesday. This one looks as if it is
more likely to move right over us, so precipitation looks more
likely for much of the area. Snow levels will remain low with this
one, in the 1500 to 2500 foot range. This one appears to be
another light to moderate snowfall event. With the vigorous upper
level low aloft, suspect that brief, but substantial
accumulations will again be a concern.

Finally, current guidance indicates a break in the action
beginning Tuesday or Wednesday. We'll keep our fingers crossed on
this development, as reprieves in the extended have been slower to
materialize much of this winter and have been of shorter duration
than what they often appear to be from afar when they do arrive.
BTL

MARINE...Updated 330 AM PST Thursday 23 February 2017...Steep
seas are expected to develop from west to east this morning as fresh
swell moves into the waters with a dominant period of  8-9 seconds.
Seas of 7 to 8 feet at 8 seconds are expected this morning with
marginal small craft advisory conditions. Seas steepness will
subside in the afternoon. Low pressure moving down the Pacific
Northwest coast on Friday should increase winds and seas. Models
have trended lower with the south to southwest winds though, so do
not expect small craft advisory conditions. Another disturbance will
shift south on Sunday but may stay along the coast or inland. So
expect mainly expect northwest winds and seas dominated by northwest
swell. -CC

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Watch from Friday morning through Saturday morning
     for ORZ021-022-024.

CA...Winter Storm Watch from Friday morning through Saturday morning
     for CAZ080.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas
until 10 AM PST this      morning for PZZ350-356.      Small Craft
Advisory for hazardous seas until 4 PM PST this      afternoon for
PZZ370-376.

BMS/BTL/MAP