Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 252144

Area Forecast Discussion
National Weather Service Medford OR
244 PM PDT SUN SEP 25 2016

.DISCUSSION...A very dry air mass is in place across the region
this afternoon with a virtually cloudless sky. The nearest stratus
is about 130 miles offshore of Cape Blanco. A Chetco effect has
brought heat all the way to the coast at Brookings with a
temperature of 95 degrees as of 2pm. Even the remainder of the
coast is in the mid 70s early this afternoon. High pressure aloft
will continue to be the dominant force into early this week with
the ridge axis moving onshore tonight. Other than patchy fog in
the coastal river valleys, skies will be clear. Low-level
offshore flow that was gusty over the mountains last night will
ease tonight, but it will remain quite warm and very dry over the
upper slopes and ridges. Valleys will cool readily after sunset,
so a steep inversion will develop once again.

With the surface thermal trough moving inland tomorrow, cooling
will begin at the coast as onshore flow develops. We`ll see a
return of stratus to parts of the coast, if not during the day,
then certainly tomorrow night. Inland areas will remain sunny and
very warm to hot, but shy of records. The marine push tomorrow
night will bring low clouds and perhaps even some drizzle along
the coast and into portions of the lower Umpqua Valley. Stratus
will likely spread all the way to the Umpqua Divide, but will be
too shallow to get into the Rogue Valley, at least here in
Medford. Perhaps some low clouds or fog make it into the Illinois

Though not as hot as Monday, unseasonable warmth will continue
for inland areas both Tuesday and Wednesday afternoons with high
temperatures averaging about 8-12 degrees above normal. It will
remain dry.

The weather pattern will begin to transition toward cooler and
wetter late this week as an upper level trough digs southeastward
from the Gulf of Alaska. Southwest flow aloft will increase
Thursday afternoon and expect some gusty winds to develop east of
the Cascades. Even though we`ll begin to cool down and humidity
should still be a notch above critical levels, we`ll have to
monitor this for potential fire weather concerns. Isolated showers
could develop over the Cascades, especially north of about Lake of
the Woods, but instability parameters still look marginal, so
have not included thunder.

The upper trough will likely set up somewhere near or just off
Vancouver Island Friday into the weekend. This will allow multiple
disturbances to rotate onshore, each bringing a chance of
precipitation along with a significant cool-down. We`ll see
temperatures nose-dive during this time frame, with daytime highs
probably 5-15 degrees below normal. Precipitation chances will be
highest along the coast and into the Umpqua Valley over to the
Cascades with many areas along and west of the Cascades likely
receiving wetting rainfall. Snow levels will drop to about 5500
feet, which means the mountains could see some accumulating
snowfall, most likely during the nights. -Spilde


.AVIATION...25/18Z TAF CYCLE...VFR conditions are expected through
the next 24 hours over most of the area. Along the north coast,
including KOTH, patchy fog and stratus is likely to return late
tonight and persist until around 17Z Monday morning. -DW


.MARINE...Updated 230 PM PDT Sunday 25 September 2016...A thermal
trough will keep moderate north winds and wind driven seas going
over most of the area through tonight. The trough will weaken
briefly on Monday with lower winds and seas...but it will redevelop
Tuesday into Wednesday after a weak front moves onshore. Models are
consistent in showing low end gales over the southern outer waters
Tuesday afternoon through Wednesday afternoon. Given the models have
been showing this for the past few runs, decided to go with a gale
watch for zone 376 mainly south of Cape Blanco starting Tuesday
afternoon and going until Wednesday afternoon. Elsewhere, winds will
be weaker Tuesday afternoon through Wednesday afternoon, but will
still reach small craft conditions.


.FIRE WEATHER...Updated 230 PM PDT Sunday 25 September 2016...
Compared to last night, easterly winds will be weaker tonight but
it will remain very dry with poorer recoveries at mid slopes and
ridges. With the weaker winds, red flag warning conditions are not
expected but the extreme dryness warrants headlining.

With an upper ridge in place and surface thermal trough moving
inland, it will be hot and very dry inland on Monday with highs
approaching though not exceeding record levels. Coastal humidities
will improve Monday afternoon, but gusty northerly winds will
develop at the coast on Tuesday.

With the thermal trough moving farther inland Tuesday, humidities
will creep up and inland temperatures get a modest start to a
cooling trend. After very slight additional cooling on Wednesday,
temperatures will be noticeably cooler Thursday. But, the most
notable aspect of conditions on Thursday will be increasing westerly
winds at 10 to 20 MPH on the east side in the afternoon. These winds
will likely trend stronger at 15 to 25 MPH on Friday but it will be
dramatically cooler with below normal temperatures.

The cooling will continue into the weekend as an upper low sends a
series of systems into the area. A system may bring a wetting rain
to the coast and Umpqua Valley Friday then to much of the area next
weekend. It is too early to know exactly how much rain falls or
where it falls, but confidence is fairly high that the pattern will
shift to be much cooler and wetter late this week. -DW




Pacific Coastal Waters...Small Craft Advisory for hazardous seas
     until 5 AM PDT Monday for PZZ350-356-370-376.
     Small Craft Advisory until 5 AM PDT Monday for PZZ376.


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