Small Craft Advisory 65, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
834 PM PDT Fri Jul 20 2018

.DISCUSSION...Current observations around the area include smoke
in many of the west side valleys. Current Visibility at KMFR is
locked in at one and three quarters of a mile, however to the
north, visibilities are better. To the south (toward Ashland),
visibilities are likely even worse. The smoke extends all the way
from the Coast south of Gold Beach all the way to Bly and many
areas south in between.

Meanwhile, observations in the Illinois Valley are showing
conditions very near Red Flag (15% humidity and gusts to 21 mph).
Have gone ahead and extended that Red Flag warning for 2 hours to
remain on the safe side. That being said, am considering another
red flag warning for tomorrow afternoon for the Illinois Valley
and portions of the Coastal Range. This could impact the Klondike
and the Granite fires. Additionally, it appears as if Modoc County
could reach near critical fire levels as well, but this is
particularly complex since we have a slight chance for a
thunderstorm or two in Modoc County in which moisture will need to
be present. Thus, will need to investigate a little bit further
before making any decisions.

Otherwise, the main concern for the forecast period is to look at
the timing and location of potential thunderstorms for Sunday.
The trigger remains weak, although moisture still looks pretty
high. Am not making any changes to the forecast in this update for
tonight, but there is lots to look at. -Schaaf

&&

.MARINE...Updated 800 PM PDT Friday 20 July 2018...High
pressure offshore and a thermal trough at the coast will persist
through Saturday night with gusty north winds and very steep wind
driven seas. Made a few changes tonight reducing the area of gales.
Buoy 27 hasn't reported gales for the last few hours.  Still have an
area of gales beyond 10 nm of shore, but within 10 nm of shore and
south of Cape Blanco, it will just be hazardous seas.

Winds and seas will then see a weakening trend late Saturday night
into at least Wednesday. The weakening will be due to the thermal
trough moving inland with high pressure building into the waters.
Though conditions will be improved, steep seas are likely on Sunday
and are also possible in the outer waters south of Cape Blanco on
Monday. Northerly winds may increase on Thursday into Friday.

-Petrucelli/Smith

&&

.PREV DISCUSSION... /Issued 608 PM PDT Fri Jul 20 2018/

DISCUSSION...Updated 300 PM PDT Friday 20 July 2018...The
forecast has become increasingly complex and impactful, now that
we have multiple active fires, smoke and unhealthy air quality,
another heatwave on the way, and more chances for thunderstorms.

Temperatures today are running about 5 degrees lower than
yesterday for areas that have the heaviest smoke, and temperatures
are higher than yesterday by about 5 degrees in areas outside of
the smoke in the Umpqua Basin around Roseburg.

Tomorrow temperatures should trend upward by a few degrees, with
readings about 5 degrees above normal for this time of year. Just
enough moisture will creep up from the south to bring a slight
chance for thunderstorms into the southeast portion of Modoc
County. Latest model data suggests no thunderstorms, but after
observing the models going back and forth the past few days, we
decided to keep in the slight chance of thunder there.

On Sunday, we'll have a combination of trigger, moisture, and
instability to support thunderstorm chances. The trigger will be
weak shortwave energy moving up from the south. This is noticeably
weaker than the energy that brought the thousands of cloud to
ground lightning strikes last Sunday, but it should be enough to
kick off some thunderstorms. The moisture is certainly sufficient
with PW values near an inch and a large area of H5-H7 humidity of
60% or greater. Lastly, H8 computed Lifted Index values of -2C to
-3C and CAPE values near 1000 J/kg suggest enough instability to
support thunderstorms. Even areas that see isolated thunderstorm
coverage could see a significant amount of new lightning starts  due
to the very dry vegetation. Please see the fire weather  discussion
below for more details.

Temperatures begin a significant trend upward on Monday, and the
hottest conditions should last through Wednesday. Smoke will likely
prevent many areas from experiencing the full extent of the heat,
and we've kept temperatures slightly below guidance for now.
Tomorrow, we'll continue to evaluate and consider a heat advisory or
excessive heat watch for areas. Instability does hang around Monday,
and will continue to bring a slight chance for thunderstorms, though
chances don't look as high as Sunday.

Another hot day is expected Wednesday, and then there are some model
differences in terms of when cooling will occur. The GFS suggests
cooling by Thursday, while the EC maintains the heat. If past is
prologue, we'll likely be in store for at least another very hot
day.

-Keene

AVIATION...For the 21/00Z TAFs...Wildfire smoke continues over many
of the inland valleys west of the Cascades. Lower visibilities along
with IFR/MVFR Cigs will exist near these fires. The Garner
complex and fires to the north continue to undergo significant
activity and smoke output this afternoon and evening. IFR
visibilities are occuring at MFR due to this increased smoke
output. During the last two evenings, the smoke clearing out
briefly at MFR with the increased northerly winds. Moderate to low
confidence this will happen considering how thick the smoke is at
1z.

At the coast, the main concern will be gusty north winds, north of
Cape Blanco through this evening with gusts to 35 kts likely at
North Bend. VFR cigs will continue through this evening. Guidance
hints at marine stratus developing around daybreak Saturday with
MVFR cigs, but more likely the cloud cover will be scattered and
this is indicated in the TAF. Gusty north winds will be a concern
again for similar locations at the coast.

-Smith

FIRE WEATHER...Updated 330 PM PDT Friday 20 July 2018...

A thermal trough pattern will continue to deliver north winds and
dry conditions to the forecast area. Burning periods will gradually
lengthen through Saturday at least. North to south valleys will be
favored for the strongest winds into this evening, and this will
combine with low humidity in the Illinois Valley portion of FWZ620,
and a Red Flag Warning for that area continues to highlight these
expected conditions.

Saturday will see north winds trending lower but west winds on the
East Side of the Cascades will increase some. Additionally, moisture
and instability will increase some from the south and bring a slight
chance for thunderstorms to eastern Siskiyou and Modoc Counties.
Winds and RH may combine again in the Illinois Valley again Saturday
afternoon, and will see if the next model runs continue to trend
this way and issue a watch if they do.

Thanks to a disturbance to the north and some southerly flow to the
ridge levels, the thermal trough and gusty north wind pattern
weakens on Sunday. Models continue to show the thermal ridge moving
inland into the Cascades Sunday. This would create a very dry and
steep lapse rate near the ground. This will combine with cooler
temperatures moving in aloft and an unstable air mass developing
over much of the region. Each model run continues to creep the area
of instability farther north into the west side of Oregon, and the
current watch may creep farther north by the time we reach the
Sunday time frame. These thunderstorm chances basically cover the
Siskiyous southward and Cascades eastward. Although we are only
expecting isolated thunderstorms over the west side Saturday, ERC's
and 1000 hr fuels are at record levels and over the west side the
almost every strike resulted in a start last Sunday. Instability
weakens but remains over the region Monday, but with weak steering
winds anything that develops should latch to terrain.

-Sven

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Sunday afternoon through Sunday evening
     for ORZ621>625.
     Red Flag Warning until 10 PM PDT this evening for ORZ620.

CA...Fire Weather Watch from Sunday afternoon through Sunday evening
     for CAZ280>282-284-285.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Sunday for
     PZZ350-356-370-376.
     Gale Warning until 5 AM PDT Sunday for PZZ356-376.
     Hazardous Seas Warning until 5 AM PDT Sunday for PZZ356-370-376.

BMS/CZS/NSK