Dense Smoke Advisory 5, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
900 PM PDT Sat Sep 2 2017

.DISCUSSION...Evening update. Smoke continues to become more dense
through much of the region. With the upper ridge continuing to shift
slowly east the offshore flow has been replaced with a southerly BL
flow, and this will bring increasing moisture to the region. I have
adjusted the area of slight chance of thunderstorms to mostly along
the Cascades and slight to the west of south, and over the the east
side,west of the Winter Ridge. The dense smoke should inhibit any
develop and have removed any chances where the smoke is very dense.
Sven

.DISCUSSION...Hot weather and smoke will continue in inland areas
through Labor Day, with triple digit temperatures expected in
west side valleys. The exact high has been a challenge to
forecast, as smoke cover limits heating...but fluctuations in
smoke thickness in the afternoon can really make or break the
forecast. In any case, it will be hot, and air quality impacts
will continue across much of the area with significant smoke
extending from the Cascades and west, as well as eastward into the
upper Klamath basin at times. An air quality alert and an
excessive heat warning remain in effect.

The surface inversion in the Rogue Valley has broken. Since smoke
has been concentrated near the surface and more sparse aloft,
expect some smoke to mix out, and air quality and visibility to
improve slightly, though we will stay in the unhealthy range. As
daytime heating continues, upvalley flow should kick in and bring
more smoke towards the valley from fires to the west and
northwest.

Sunday, models indicate slight mid-level moisture and
instability. The NAM shows a few weak disturbances moving over the
East Side. This brings the possibility of thunderstorms over the
Siskiyous and into the Cascades and east towards Winter Rim.
Possible triggers look weak, so limited probabilities to slight
chance.

Tropical storm Lidia is currently situated just offshore of Baja
California. She will move north/ northwestward over the next
several days, transporting moisture into the Medford CWA. This
will support thunderstorm chances, with Wednesday having the
highest confidence in the short term as southerly flow brings a
few weak triggers.

The remnants of TS Lidia should be offshore of southern Oregon/
northern California by Thursday... and expect a steep decline in
afternoon high temperatures beginning Thursday as the upper ridge
degrades. By Friday, temperatures should be very close to climo.
-MSC

&&

.AVIATION...02/18Z TAF CYCLE...West of the Cascades, smoke from area
wildfires is causing widespread MVFR visibilities with local IFR
visibilities closer to the wildfires. With lighter winds, mixing is
expected to be weaker today leading to a gradual worsening of
conditions through the day into tonight. As for any coastal stratus
or fog...dry, offshore flow will keep stratus far offshore through
Saturday night.

East of the Cascades...VFR conditions prevail today with the
majority of smoke well west of the area. However, easterly low level
winds are expected to turn westerly after sunset and this should
allow smoke from wildfires along the Cascade crest to filter
eastward into Klamath and Lake counties, including KLMT then persist
into Sunday. -KS

&&

.MARINE...Updated 200 PM PDT Saturday 2 September 2017...Aside from
breezy northerly winds expected this evening and again Monday,
relatively calm seas and light winds are expected through at least
mid-week. The thermal trough has expanded north today, pushing the
stronger northerly winds associated with it into the northern outer
waters. These stronger winds will peak this evening, diminishing
overnight into Sunday morning. Models have shortened the duration of
the increase in northerly winds and now only show the increase from
early Monday morning through late Monday evening. While expected to
remain below small craft advisory levels, the strongest winds will
be south of Cape Blanco. Winds are likely to reverse to light
southerly Tuesday night with seas then expected to become westerly
swell dominated for the first time in quite a while by
Wednesday...likely hovering around 4-6 feet at least into early
Friday. -DW/BR-y

&&

.FIRE WEATHER...Updated 200 PM PDT Saturday 2 September 2017... Dry
and hot weather will continue this afternoon. The latest visible
image shows patchy to areas of smoke mainly west of the Cascades.
Areas that have the thickest smoke will have a harder time heating
up during the afternoon. Winds will not be as strong today as the
thermal trough overhead weakens the pressure gradient. This will
contribute to increased smoke thickness/weaker mixing which may
adversely affect air operations.

The models show marginal instability Sunday afternoon and evening,
mainly in northern California. We currently have a slight chance of
thunderstorms in the higher terrain in Fire Zone 280, western 282
and portions of Fire Zone 284 and that looks reasonable. We also
have a slight chance of thunderstorms for the northern Cascades and
eastside, but not as convinced we'll get anything there. For now
we'll keep a slight chance in these areas, but most likely we'll get
nothing more than some cumulus build ups.

Recoveries will be poor over the mid slopes and ridges tonight,
especially in Fire Zones 618, 619, 621 and 280, but winds are
expected to be lighter. Sunday night will be a close call. The
models show a thermal trough developing along the coast Sunday night
with a chance for moderate northeast winds and poor recoveries. The
models suggest winds may not be strong enough, but close enough to
warrant a Fire Weather Watch.

Meanwhile, a red flag warning still remain in effect for the
Cascades eastward in southern Oregon for very hot, dry, and unstable
conditions until this evening on existing wildfires as the thermal
trough moves farther inland. This includes the North Umpqua Complex,
Rattlesnake, High Cascades Complex, Naylox, and Jade Creek, and any
other fires from the Cascades eastward. Please see RFWMFR for more
details on this.

The 00Z GFS and NAM have been consistent in bringing an increase in
700-500 mb moisture on Sunday which will lower the Haines to a 5 for
most of the area, but a 4 for inland portions of southwest Oregon.
The one exception will be the Warner Mountain region that is likely
to have another day with a Haines of 6.

Extreme heat and poor humidity recoveries will affect most higher
terrain areas through Wednesday morning, with the lowest readings
through Monday morning. This will result in nearly non-stop burning
periods for active fires across the forecast area.

At this point, it looks like any moisture or energy associated with
the remnants of Lidia won't affect the area through Tuesday at
least. The risk of thunderstorms will be marginal Monday through
Tuesday, though southerly flow around the Great Basin upper ridge
will bring moisture and weak triggers into the forecast area.
However confidence remains low where and if thunderstorms will
develop.

Wednesday afternoon through Wednesday night could be problematic in
terms of thunderstorms. The models are in fairly good agreement
showing the remnants of Lidia getting advected into our region
Wednesday. At the same time the upper trough (remnants of Lidia) will
become negatively tilted as it moves north in response to the
upstream upper trough from the eastern Pacific. The pattern that the
models suggest could be one that could lead to a thunderstorm
outbreak from Wednesday afternoon through Wednesday night and
possibly into Thursday. Keep in mind this is not a slam dunk as
were still several days out and the details on this are likely to
change, but it's something that we need to be aware of.

There is less uncertainty with the details late next week. The
models are starting to come into better agreement with the overall
pattern,. We could be looking at cooler and wetter conditions next
Thursday and Friday. There is even some evidence that west side
locales could receive a wetting rain. But, there is also the
possibility of additional embedded thunderstorms as well as gusty
winds associated with a frontal passage. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 8 PM PDT this evening for ORZ617-623-624.
     Excessive Heat Warning until 11 PM PDT Monday for ORZ021>028.
     Fire Weather Watch from Sunday evening through Monday morning
     for ORZ618-619.

CA...Excessive Heat Warning until 11 PM PDT Monday for CAZ080.
     Heat Advisory until 11 PM PDT Monday for CAZ081-082.
     Fire Weather Watch from Sunday evening through Monday morning
     for CAZ280.

Pacific Coastal Waters...None.

MSC/MAP/MNF