Fire Weather Watch 31, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
1123 AM PDT Mon Aug 16 2021

Updated AVIATION Section

.UPDATE...Smoke is beginning to clear from the area, slowly but
surely, as west winds pick up ahead of the front expected to pass
through the area later today. By tonight, suspect that most of
the smoke should clear out, with the exception of areas directly
downwind from active fires. Have made some adjustments to the
near term forecast this morning to account for this trend, and
adjusted the sky cover to bring it in line with the marine layer
stratus, which made a significant push into the coastal valleys
this morning. As a result of the passing front, and an even
stronger marine push tomorrow, the area should see the coolest and
clearest (in terms of smoke) day in some time.

No other changes are necessary, but forecast efforts today will
likely focus on smoke, marine layer clouds, and the potentially
cooler than previously expected forecast in the long term. -BPN

&&

.AVIATION...16/18Z TAFs...Along the coast, MVFR/IFR marine stratus
will erode with just some broken MVFR ceilings lingering into
this afternoon north of Cape Blanco. Expect VFR to develop on nearly
all of the Curry coast this afternoon into early this evening. A
deeper marine surge will move onshore tonight into Tuesday morning
with MVFR ceilings and even a bit of light rain and drizzle likely
into the Umpqua Basin/west slopes of the Cascades. Clouds will
also likely reach the Siskiyous with some of the higher terrain
around the Rogue Valley possibly getting some light rain Tuesday
morning with this surge.

Wildfire smoke is still limiting visibility across northern
California and from eastern Douglas and northeast Jackson counties
eastward in Oregon today. However, increasing west-northwest winds
this afternoon through Tuesday will cause improving visibility
from northwest to southeast. Areas immediately downwind of the fires
will still maintain some smoke impacts though. -Spilde

&&

.MARINE...Updated 800 AM PDT Monday, 16 August 2021...
Relatively light winds and low seas will continue through this
morning. A thermal trough will strengthen with advisory level
north winds expected south of Port Orford by this afternoon and
evening. A dry cold front will then move through tonight. Then,
south of Cape Blanco, northerly gales are possible Tuesday and
Wednesday with very steep seas. North of Cape Blanco, winds and
seas are likely to build to advisory levels after Tuesday, mainly
beyond 10 nm from shore. The great majority of the sea condition
Tuesday through late week will result from local winds, but a
combination of steep to very steep local wind waves and a slightly
longer period fresh swell look possible to evolve later in the
week. ~BTL

&&

.PREV DISCUSSION... /Issued 530 AM PDT Mon Aug 16 2021/

DISCUSSION...

There are still some warm temperatures in some of the valleys
early this morning as the heat lingers. We did expire the heat
advisory Sunday evening as temperatures are expected to be a tad
bit cooler Monday afternoon and evening. There is a little bit
uncertainty with this as the cooler air appears to move in after
the hottest time of day. In any case, we do have high confidence
cooler air will arrive by the late evening hours, which will help
provide relief to the heat we've been seeing over the last week.

A cold front is forecast to push through southern Oregon and
northern California some time between roughly 10 pm Monday and 5
am Tuesday. We are forecasting a 20% chance of drizzle in the
Umpqua Basin as quite a few models are forecasting a little bit of
precipitation. Conditions dry as the front moves south overnight.
This front and wind direction change will help clear out the
smoke further. Smoke plumes are forecast to charge towards the
south east throughout Monday and Tuesday. Locations along the
coast and west of the Cascades should escape most of the smoke.
East of the Cascades, some lower concentration smoke could build
into areas. None the less, stay tuned for another update to the
air quality alert on Monday afternoon.

By Tuesday afternoon behind the front, winds should be rather
breezy with some drier air filtering into the region. We are
confident many locations east of the Cascades will see wind gusts
around 25 mph as drier air settles in. This has raised fire
weather concerns and is discussed in a little more detail in the
fire weather discussion below.

As the upper level low departs the region, a coastal thermal
trough will build with some 10 to 15 mph north east winds along
the coastal range Wednesday. These winds will help warm up
coastal locations, such as Brookings. Highs will push into the mid
70's and perhaps up to 80's along the southern Oregon coast.

Beyond Wednesday, the pattern becomes stuck in limbo with a deep
upper level low well to our east near Montana and Idaho and a
broad area of high pressure of the Pacific. This will result in
deep northerly flow Thursday through Friday. Temperatures should
stay around normal values for Thursday and again Friday. Models
suggest another upper level low coming down in this flow pattern
sometime around Friday or perhaps Saturday. This wave will likely
be dry, but it will continue to bring northerly flow and near
normal temperatures.

-Smith

&&

FIRE WEATHER...Updated 835 AM Monday August 16 2021...

Today into Wednesday, we'll have a cooling trend as an upper
trough begins to move into the area with the concerns shifting to
winds and low relative humidities. Winds and RH, although lasting
probably for only around three hours, will meet warning criteria
this afternoon into the evening in Modoc county. Tonight a strong
marine push will bring light rain and drizzle to portions of the
west side north of the Umpqua Divide. There's strong evidence a
stronger upper trough approaching the area Tuesday afternoon and
evening should bring in moderate to strong winds and low relative
humidities east of the Cascades, and a watch has been issued for
much of east of the Cascades. Tuesday night, a thermal trough will
set up along the south Oregon coast and we'll see increasing east
to northeast winds and moderate to possibly poor overnight
recoveries at the mid slopes and ridges in Fire zones 618, 619 and
280 Tuesday night into Wednesday morning.

Wednesday, the upper trough will shift east of the area in the
afternoon with stronger ridding building offshore. This will result
in a dry and stable northwest flow aloft over the area. We could see
afternoon temperatures heat up once again, but not the values we
have experienced recently. -Sven

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for ORZ624-625.

CA...Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for CAZ284-285.
     Red Flag Warning from 2 PM this afternoon to 10 PM PDT this
     evening for CAZ285.

Pacific Coastal Waters...Gale Watch from Tuesday morning through
     Wednesday evening for PZZ356-376.
     Small Craft Advisory from 2 PM this afternoon to 8 AM PDT
     Tuesday for PZZ356-376.