Wildfire in Oregon, August 22 to 31, 2018

Area Forecast Discussion
National Weather Service Medford OR
848 AM PDT Wed Aug 22 2018

.UPDATE...The area remains shrouded in smoke, and will likely
remain so through tomorrow morning, when the next front arrives.
How much the smoke clears with this front remains to be seen, but
we do expect significant improvement away from the fires. Areas
near and downwind of the various fires may not see much
improvement, as smoke production may increase due to increased
winds. Conditions will trend cooler and slightly more humid behind
the front and into the weekend. There is a chance, although quite
small, that rain may fall over portions of the region next week.

No major changes were necessary this morning, other than to bring
marine layer stratus and fog inland a bit further, as satellite
imagery shows this morning.

For more information on this and the rest of the forecast, see
the previous discussion below. -BPN

&&

.AVIATION...For the 22/12Z TAFs... IFR to LIFR conditions will
continue along the coast as coastal stratus settles in.  This is
expected to lift later this morning. Over the remainder of the area,
Widespread MVFR vsbys with areas of IFR vsbys are expected due to
wildfire smoke tonight through Wednesday night.

-Smith/Spilde

&&

.MARINE...Updated 800 AM PDT Wednesday 22 August
2018...Relatively light winds and seas will prevail through
Thursday morning. A thermal trough will strengthen Thursday
afternoon into Saturday, bringing stronger north winds and choppy
wind driven seas, mostly from Cape Blanco south. Brief gales are
possible late Friday afternoon and early Friday evening in a small
area south of Brookings and beyond 10 NM from shore. The thermal
trough will weaken Saturday night, and winds and seas will
diminish at that time. Areas of wildfire smoke will persist today
through tonight bringing haze and minor visibility reductions
aside from the normal reductions associated with the marine layer.
Winds become favorable to push smoke out of most the coastal
waters during the day Thursday, except for lingering smoke
expected over southeast portions of the waters near the southern
Curry coast. -Spilde/CC

&&

.FIRE WEATHER...Updated 300 AM PDT Tuesday 21 August 2018...In
addition to local wildfire smoke sources, substantial smoke
continues to drift southward over the area from wildfires to our
north from northern Oregon, Washington, and British Columbia. From
the Siskiyous southward, and across portions of Modoc County,
however, there's less smoke, which is allowing fires to burn more
freely.

For the next two afternoons, expect low RHs and breezy winds over
much of the area. The primary concern will be in FWZ 625 and 285,
where winds and humidity may very well reach critical levels
Thursday afternoon and evening due to the passage of a dry cold
front. A Fire Weather Watch has been issued for those areas. FWZ 624
appears close, but not quite within the major area of concern, but
if models trend drier or windier, portions of FWZ624 could  be added
to the watch area.

A cooler trend is expected for later this week into early next week
as an upper trough deepens over the region. There is also some
possibility of light rainfall over northern portions of the area,
mainly from the Coos and Douglas coast inland into the Umpqua basin
and south central Oregon Cascades. However, the slight chance for
showers also includes portions of northern Klamath and northern Lake
counties Sunday night into Monday. Confidence is low in the details
of this portion of the forecast due to variability on the strength
and track of the upper trough over the region. -CC

&&

.PREV DISCUSSION... /Issued 313 AM PDT Wed Aug 22 2018/

DISCUSSION...

We saw cooler than expected temperatures yesterday because of the
smoke and we expect this cool trend to continue into Wednesday
given the fire activity Wednesday morning. We cooled temperatures
down a tad today with highs in the lower 90's in the west side
valleys and mid 60's along the coast.

The next topic is the approaching trough on Thursday afternoon and
evening. The positively tilted trough will bring some winds east
of the Cascades and along higher terrain. This has prompted the
fire weather watch for Thursday afternoon. After this trough
passes, we'll be on the backside of a cooler and well mixed
airmass. We expect some of the smoke that has built up in the
valleys will mix out during Friday afternoon into the weekend.
People generally south east of fires may not see any change, but
the Rogue valley and the Shasta valley should see improvements
Friday afternoon into this weekend.

The other important and interesting topic is another trough
approaching the region during Sunday. Most of the ensembles and
both of the operational models are suggesting this trough will
move through the Pacific Northwest. However, A few of the
ensemble members suggest this trough becoming a cutoff low off the
California coastline. Since we are moving closer to mid
September, rain is climatologically reasonable this time of year.
Right now we're going with a slight chance for rain and rain
showers Sunday through Sunday night north of the Umpqua divide.
If we do get rain, don't expect significant changes to fire
activity. The cooler and moister airmass should help fire fighting
efforts if it doesn't rain.

-Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Thursday afternoon through Thursday
     evening for ORZ625.

CA...Fire Weather Watch from Thursday afternoon through Thursday
     evening for CAZ285.

Pacific Coastal Waters...None.