Wildfire in Oregon, August 14 to 31, 2017

Area Forecast Discussion
National Weather Service Medford OR
919 AM PDT Mon Aug 14 2017

.SHORT TERM...Low level post frontal stratus is quickly from west
side valleys south of the Umpqua Divide...and is slightly slower
to clear from the Umpqua Valley, but expect most cloud cover to
burn off by early afternoon. A shortwave brought a few lightning
strikes over southeastern Modoc County earlier this morning...
cloud cover from that system is shifting eastward. Some lingering
instability and upslope flow will support development of some
scattered cumulus over southern Modoc, but generally expect
thunderstorm threat to have passed. Expect warmer conditions today
than yesterday, as a ridge builds to the west... this trend will
continue throughout the week. Current forecast is on track, see
previous discussion for more information. -MSC

&&

.AVIATION...14/12Z TAF CYCLE... A band of IFR stratus extends from
the far northern California coast to near Brookings and will persist
until around 17Z. Also, a mix of MVFR and VFR stratus in southwest
Oregon valleys will gradually dissipate between 16Z and 20Z.
Meanwhile, a band of thicker VFR clouds will exit Modoc and Lake
counties early this afternoon with a few light showers or a
thunderstorm possible. Otherwise, a band of VFR high clouds is about
to reach the coast and will move through the area today. Conditions
will remain VFR this afternoon and evening before local MVFR cigs
develop at the coast around 06Z. -DW

&&

.MARINE...Updated 500 AM PDT Monday 14 August 2017...A pattern
of High pressure offshore and a thermal trough at the coast will be
long lasting. North winds will increase into this afternoon and
increase further on Tuesday with gales likely to develop south of
Cape Blanco on Tuesday afternoon. Gales then persist at least
through Thursday night and likely into the upcoming weekend. A
moderate northwest swell of around 3 to 5 feet will accompany steep
to very steep wind dominated seas. Winds and seas will be highest
south of Cape Blanco...especially south of Gold Beach beyond 5 NM
from shore. -DW

&&

.FIRE WEATHER...Updated 500 AM Monday 14 August 2017...

Yesterday's cold frontal passage left sufficient low level moisture
for stratus to develop in southwest Oregon valleys this morning.
These clouds will dissipate by afternoon while a fast moving
disturbance will bring a slight chance of showers and thunderstorms
to the Warner Mountains area into early this afternoon. A band of
high clouds will move through today and a drying and warming trend
will begin with slight warming. The warming and drying trend will
continue through the week with poor to moderate overnight mid slope
and ridge top humidity recovery beginning tonight. Humidity recovery
will be worst on Tuesday night and on ridges west of the
Cascades...especially in the Kalmiopsis Wilderness and coastal range
of far southwest Oregon.

Thunderstorms do enter the picture again at least through Friday
which will leave the above normal temperatures and low to moderate
humidity levels as the focus of the week. The combination of drying
and warming conditions, along with seasonable afternoon breezes,
provides the potential for sleeper fires to "wake up" this week.
-DW

&&

.PREV DISCUSSION... /Issued 250 AM PDT Mon Aug 14 2017/

DISCUSSION...A cold front moved through the forecast area yesterday,
and looking at the 24 hour changes in terms of observations, the
main element that sticks out is relative humidity. Humidity behind
the front is up 10 to 20 percent compared to yesterday at this
time, and this should generally have a dampening effect on area
fire activity this morning, helping to limit smoke production.
Though the air mass has cooled, morning surface temperatures have
been moderated because of the cloud cover and are similar to
yesterday at this time. GOES-16 imagery shows the marine
layer/inversion wiped out, and this is confirmed by the North Bend
profiler, so we're just dealing with post-frontal low level
moisture and associated clouds mainly banking up against terrain.

A potent shortwave is moving through the southern half of the
forecast area this morning, and models (mainly the GFS) have been
hinting for the past several days at morning convection over Modoc
and Southern Lake Counties. Model trends have the moisture and
instability pushing through quicker, and we have followed suit
with the most recent forecast. It looks like chances for any
thunderstorms are out of the area by early afternoon.

Today will feature a few degrees of warming compared to yesterday
and significantly less cloud cover. We've maintained the idea from
the previous forecast of limited smoke coverage for much of today,
then increasing late with the potential of increasing smoke
production from area fires. As the week progresses, we're thinking
generally less smoke for areas away from fires in the mornings and
then increasing chances for smoke in the afternoons when fires are
more active and smoke aloft can mix down to the surface. All this
will of course will have to be evaluated and adjusted day to day
based on fire activity.

At the coast, GFS boundary layer and near-surface humidity suggests
marine layer clouds really won't be extensive until around Thursday
morning when the marine layer re-establishes itself. We are
forecasting patchy coastal fog most mornings. As offshore northeast
winds increase this week, Wednesday could be a hot one at Brookings,
and we have maintained a high temperature forecast in the mid 80s
there.

Summarizing the week for inland areas, the general forecast is for
warming and drying conditions through Saturday before upper
troughing approaches from the northwest and cools the air mass.
Given the trajectory of the pattern-changing upper trough, from
northwest to southeast, a thunderstorm outbreak does not look likely
at this time. With that said, this is a ways off and subject to
change. Let's end this discussion by pointing out the problematic
timing of this upper trough, as it could bring low clouds to areas
west of the Cascades (especially north of the Umpqua Divide) on
the morning of the Great American Eclipse.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

Pacific Coastal Waters...Gale Watch from Tuesday afternoon through late Thursday night
     for PZZ356-376.
     Small Craft Advisory until 5 AM PDT Friday for
     PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 5 AM PDT Friday
     for PZZ350-356-370-376.
     Hazardous Seas Warning until 5 PM PDT Tuesday for PZZ356-376.

MSC/DW/SK