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fxus66 kmfr 261106 
afdmfr

Area forecast discussion
National Weather Service Medford or
306 am PST sun Feb 26 2017

Discussion...low pressure is moving south along the Washington
coast now, and light to moderate precipitation has spread to
inland locations. The low is moving at a fast clip, but the upper
level energy associated with it will slow some as it nears the
forecast area and turns eastward later today, remaining in the
vicinity through tonight.

The overall forecast hasn't changed much, and the challenge
continues with determining low elevation snow impacts as a potent
cold low with moderate to perhaps heavy precipitation arrives
during the daytime hours in late February. A frontal boundary and
associated band of precipitation is expected to arrive later this
morning at the coast and in the Umpqua basin. This precipitation
will progress southeast through the forecast area through the day.
Snow levels will generally be between 1000 and 1500 feet through
today, well below the freezing level given the expected vigorous
shower activity (with thunderstorm potential towards the coast)
and resulting downward mixing of colder air towards the surface.
This cold and unstable air mass will first bring periods of slushy
snow accumulations (few inches possible) to Camas Mountain on
Highway 42, Canyon Mountain and Sexton pass on Interstate 5 and
Highway 99 at Hayes Hill. As the precipitation arrives, Road
surface temperatures will be rising some, but we think that some
heavier snow showers will counteract this and again, result in
occasionally wintry travel conditions. It is possible that some of
these passes could see snow this morning, switching to rain/snow
mix this afternoon, and then snow again late this afternoon and
this evening. Tonight in these areas, snow will more readily stick
to roads, but shower coverage is expected to be less. At higher
elevations, snow will definitely cover the roadways and result in
difficult travel. Mountain passes in the high Cascades are covered
in winter weather advisories too, through tonight.

Confidence is lower in terms of how snow will impact valley
locations like the rogue and Applegate valleys. We're confident that
some areas above 1500 feet in Jackson County (as well as areas known
to overachieve in snow events like Evans valley) will see brief
periods where some roads are snow-covered and visibility is reduced
significantly. If showers are heavy enough, this could even occur
this afternoon as Road and air temperatures are peaking. It's
difficult to pin down which locations will see the greatest impacts,
but we thought it prudent to broaden the coverage area of the Winter
Weather Advisory and include portions of the Applegate and rogue
valleys. More reason to expand the advisory is the idea that the
models are all now in agreement with two pieces of energy aloft
moving through late this afternoon, providing more chances for
enhanced snow shower activity. We have left out the lowest
elevations where impacts are less likely. A Winter Storm Warning
continues for the foothills of the Cascades where uncommonly heavy
snowfall is expected for late February.

Tonight, showers should diminish in coverage, but snow levels will
be lowering, and the potential for some snow accumulation
continues. We have winter weather advisories ending at 4am PST
Monday morning due to expected waning shower activity. Conditions
will certainly improve by late Monday morning as Road and air
temperatures rise. Models show another shortwave moving through
with more showers during the day Monday, but impacts should be
limited because of the warming daytime temperatures. More snow
showers are possible Tuesday, mainly along the Cascades and from
the umqpua Divide northward, but coverage will be gradually
diminishing compared to Monday. Snow levels on Tuesday should be
2000 feet or higher in the afternoon. The previous long-term
discussion follows.

Wednesday through Saturday...things will start off
fairly quiet with a broad area of high pressure building over the
area from Wednesday until Thursday. We'll eventually see a mature
low off the Gulf of Alaska slide south and produce scattered to
widespread rain along a cold front boundary. Both models are in
pretty good agreement with the timing of this, so have high
confidence some rain is on the way Friday evening. Eventually,
this low will combine with another low to pull even more moisture
in from the tropics.

We have high confidence tropical moisture will hit US in the Pacific
northwest next weekend around the Saturday Sunday time frame. Still
not sure about the exact timing or location at this point as it's
dependent on a low from Russia pulling up some moisture when it
moves over the Hawaii region, but since it's being observed, and
both models are showing rain next weekend, feeling pretty good about
the forecast at this point.

The only other note is that snow levels are expected to be around
the 5000 to 8000 foot level as there is warm moist air crashing
against the Cascades Saturday to Sunday. So we'll have to watch out
for a Cascade snow event if snow levels drop a bit lower. Stay tuned.
-Smith

&&

Aviation...26/12z taf cycle...from the Cascades west...VFR
conditions will prevail initially except for local MVFR/IFR cigs
over the valleys...but areas of MVFR cigs in mixed rain and snow
will develop this morning along the coast...spreading inland to the
Cascades by afternoon with higher terrain becoming obscured. There
will be isolated thunderstorms over the coastal waters and along the
coast this afternoon and evening. The lower conditions will persist
through Sunday night. East of the Cascades...VFR conditions will
prevail initially...then areas of MVFR cigs/vsbys in snow showers
will develop this afternoon with higher terrain becoming obscured.
The lower conditions will persist through Sunday night.

&&

Marine...updated 200 am PST Sunday 26 February 2017...a front will
move onshore later this morning. Southwest winds will shift to
northwest behind the front with very steep seas. Cold low
pressure associated with the front will bring a slight possibility
of thunderstorms this afternoon and evening. Seas will become swell
dominated tonight and will be steep through Tuesday night. Another
weak front will move onshore Monday night...then high pressure will
build Tuesday into Wednesday. A weak front will brush the area
Thursday.

&&

Mfr watches/warnings/advisories...
or...Winter Weather Advisory from 10 am this morning to 4 am PST
Monday for orz029-030.
Winter Weather Advisory from 7 am this morning to 4 am PST
Monday for orz023-024.
Winter Storm Warning from 10 am this morning to 4 am PST Monday
for orz025-026.
Winter Weather Advisory from 10 am this morning to 4 am PST
Monday for orz027-028.
Winter Weather Advisory from 10 am this morning to 4 am PST
Monday for orz026.

California...Winter Weather Advisory from 10 am this morning to 4 am PST
Monday for caz082.
Winter Weather Advisory from 7 am this morning to 4 am PST
Monday for caz080.

Pacific coastal waters...Small Craft Advisory for hazardous seas from 4 am Monday to 4 am
PST Wednesday for pzz350-356-370-376.
Hazardous seas warning from 1 PM this afternoon to 4 am PST
Monday for pzz350-356-370-376.
Small Craft Advisory from 7 am this morning to 1 PM PST this
afternoon for pzz350-370-376.

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