Sneakerwave in Oregon, January 15, 2017

Area Forecast Discussion
National Weather Service Medford OR
907 AM PST Sun Jan 15 2017

.UPDATE...An area of mid to high level clouds is pushing quickly
off to the east, leaving valley fog and low stratus as the only
other cloud cover in the area. Much like yesterday, this will be
slow to burn off, as the inversion remains quite strong and the
moist surface layer is relatively thick. The advisory for dense
freezing fog has been allowed to expire, but areas of fog will
continue through the morning.

Focus of efforts today will revolve around the upcoming wet
and windy storm expected Tuesday into Wednesday. Models have
backed off on the amount of precipitation with this system, and
lowered river forecasts reflect this. Trends indicate that the
threat of widespread flooding has diminished, but one remaining
uncertainty will be snowmelt. Will investigate further today.

Otherwise, the forecast looks on track. For more information,
see the previous discussion below. -BPN

&&

.AVIATION...15/12Z TAF CYCLE... Conditions over the next 24 hours
are expected to be very similar those observed in the past 24 hours.
IFR Low clouds and fog in the interior West Side valleys is in place
this morning. Conditions are expected to remain below field minimums
at KRBG until 20-22Z Sunday afternoon, with only low confidence that
it will become VFR then. For KMFR a lower inversion base and a
higher dewpoint means LIFR will continue at least through 18Z. VFR
is expected early afternoon at KMFR but conditions may improve only
to MVFR at KRBG and possibly the Grants Pass area.

&&

.MARINE...Updated 900 AM PST Sunday 15 January 2017...Winds will
remain weak and seas slight early today as high pressure over the
Pacific Northwest slows down an approaching front. Long period west
swell will build today leading to a period of 10 to 11 foot seas.
South winds will begin increasing Monday as the first in a series of
strong fronts approaches. Gales are possible Tuesday afternoon
through Wednesday and seas could peak in the 20 to 25 foot range
Tuesday night into Wednesday morning. Winds may increase to storm
force briefly Wednesday morning. West swell late next week could
reach or exceed 25 feet. It should be noted that there has been a
lot of model variability in terms of maximum wave heights late this
next week, with wave model guidance indicating 14 to 16 second west
swell peaking at buoy 15 in the 23 to 30 foot centered on late
Thursday.

&&

.PREV DISCUSSION... /Issued 346 AM PST Sun Jan 15 2017/

DISCUSSION...Cold conditions continue across the forecast area, with
morning low temperatures about 5 to 10 degrees below normal, coldest
east of the Cascades with temperatures there in the teens to near
zero in some spots. Strong inversions are trapping pollutants near
the near the surface, and Air Stagnation Advisories continue for
the Umpqua Basin, Illinois, Applegate, and Rogue Valleys as well
as Klamath Falls and surrounding areas.

A dense freezing fog advisory has been issued at NPWMFR through this
morning for the Rogue, Applegate, and Illinois Valleys. Webcams show
coverage of dense fog has decreased in recent hours, but conditions
can ebb and flow through the night so we will maintain the Advisory
through the early morning hours. Travelers should allow extra
time to reach their destination in the morning. Later in the
morning, fog and low clouds will lift and clear, and we have kept
generally the same timing of clearing as yesterday. The morning
Medford balloon sounding shows a slightly shallower layer of
moisture this morning, which suggests slightly earlier clearing
and perhaps more sunshine in areas like Ashland and surrounding
hills of Medford. We have trimmed areas above 2000 feet out of any
dense fog this morning.

More pronounced upper ridging builds over the area Monday, and we
expect another round of overnight and morning freezing fog in West
Side Valleys. Models have consistently pushed back the onset of
precipitation with the next front Tuesday. This means less of a
chance for any frozen precipitation east of the Cascades since some
daytime heating will occur before precipitation arrives Tuesday
afternoon. Additionally, latest operational models move through the
heaviest precipitation over the span of 12-18 hours vs. 24+ hours
like previous models have shown. This may limit the overall
rainfall amounts with this atmospheric river event. However,
heavy rain with high snow levels (above 7500 feet), on top of saturated
ground, is expected Wednesday into Wednesday night. Small stream
and urban flooding will be possible, and mainstem rivers will rise
sharply. Another inch of rain is expected in Medford, with 5+
inches in portions of coastal Curry County. A hydrologic outlook
at ESFMFR continues to highlight the flooding potential.

Snow levels drop once the front passes Wednesday, so winter
impacts to mountain passes will be possible by Wednesday evening.

In addition to precipitation, winds will be moderate to strong
ahead of the front, with about a 24 hour period of 50kt+ 700mb
flow, bringing the potential for high winds to the coast,
mountains, and areas east of the Cascades late Tuesday through
Wednesday evening.

Another hefty rain and snow-maker is expected to push through on
Friday, with winter travel concerns likely over mountain passes.
Snow levels are forecast to be around 3500 feet.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 10 AM PST Tuesday for ORZ023.
     Air Stagnation Advisory until 10 AM PST Tuesday for ORZ029.
     Air Stagnation Advisory until 10 AM PST Tuesday for ORZ024-026.

CA...None.

Pacific Coastal Waters...Gale Watch from Tuesday afternoon through Wednesday evening for
     PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 10 PM PST this
     evening for PZZ350-356-370-376.

BPN/JRS/NSK