Small Craft Advisory 67, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
858 AM PDT Sat Jul 15 2017

.DISCUSSION...No changes to the forecast are expected this
morning. There'll be some cumulus buildups this afternoon and
evening from near Mount Shasta northeastward across NW Modoc and
into portions of Lake County. There is a slight chance of a
thunderstorm in those areas, but it is more likely that nothing
happens at all and the CWA will remain dry. Overall, inland areas
will have about 3-5 degrees of cooling compared to yesterday, but
it will remain above normal. Coastal fog/stratus from Cape Blanco
northward and also near Brookings will clear off by this
afternoon. A persistent dry pattern is expected through much of
next week with just subtle changes in air mass and marine
influences along the coast. -Spilde

&&

.AVIATION...15/12Z TAF CYCLE...Along the coast and over the
coastal waters...Areas of MVFR/IFR cigs will clear to VFR by
late Saturday morning...then the lower conditions will return to the
same areas Saturday evening and persist into Sunday morning.  Over
the remainder of the area...VFR conditions will persist into Sunday
morning...but there may be some isolated afternoon and evening
thunderstorms around Mount Shasta and over eastern Lake county.

&&

.MARINE...Updated 200 AM PDT Saturday 15 July 2017...High pressure
offshore and a thermal trough near the coast will persist through at
least the middle of next week. Moderate north winds and steep seas
will continue, mainly south of Cape Blanco North gales are possible
south of Gold Beach and beyond 5 nautical miles of the coast Sunday
afternoon through Monday evening, during which time advisory level
conditions could spread north of Cape Blanco.

The areas of small craft advisory conditions was expanded slightly
over the southern outer waters into Sunday morning. Left the Gale
Watch as is for now, mainly due to uncertainty as to how much of the
northern waters will be affected by small craft conditions while the
gales are occurring over the southern waters.  Thought it better to
get more certainty in that area and then issue the warning and
advisories at the same time.

&&

.FIRE WEATHER...Updated 200 AM Saturday 15 July 2017...Hot, dry,
and breezy southwesterly to west winds east of the Cascades
(northwesterly west of the Cascades) are expected each afternoon and
evening through the weekend. Red Flag Warnings are in effect for
FWZ285 Saturday afternoon and evening for gusty winds and low
humidities.

Instability and moisture will increase into Saturday and may be
sufficient to generate isolated thunderstorms Saturday afternoon and
evening over the Mount Shasta area and and eastern Lake County.
Confidence in timing, location and development of thunderstorms
remains low and much will depend on how much moisture from remnants
of a Pacific tropical storm moves into our area. More stable
conditions should end the lightning threat on Sunday.

On Monday, the models are in pretty good agreement showing a
shortwave approaching the area from the southwest and moving through
Monday morning. This is earlier than previous model runs have
suggested...and thus the timing of the wave no longer coincides with
the maximum surface heating. Mid level moisture is still lacking and
instability parameters are marginal at best. Have taken the
thunderstorms out of the forecast for that time period. What this
impulse may impact most is the winds...enhanced southwest breezes
are possible Monday.

&&

.PREV DISCUSSION... /Issued 324 AM PDT Sat Jul 15 2017/

DISCUSSION...
The fragmented remnants of Tropical Storm Eugene moved through
last evening and overnight and, thus far, have led to no cloud-to-
ground lightning in our forecast area. There was one in-cloud
flash detected early last evening in the southeastern portion of
Fire Weather Zone 625, however. In the past two hours there have
been a couple of rogue cloud to ground bolts in Nevada near the
state line with California about 30 miles south of Modoc County,
and one strike about 30 miles east of Prineville in Crook County,
Oregon, about 50 miles to the north of our forecast area.

We'll be keeping an eye on the satellite and lightning detection
early this morning as one last mesoscale low pressure impulse
moves through in southwest flow. This more west to east oriented
impulse embedded in the southerly flow should be enough to bump
most of the thunderstorm potential for today off to our east.

We are retaining a slight chance of thunderstorms for the
afternoon and evening over eastern Lake County in Fire Weather
Zone 625 and from Mount Shasta to Medicine Lake and slightly north
of there. Like yesterday, both moisture and instability are
marginal for thunderstorm development so we'll most likely just
see some towering cumulus that fall apart once they gain much
vertical extent.

Otherwise, the low pressure trough centered west of Canada will
drift through aloft tonight drying the air mass even further in
the mid level of the atmosphere. We'll experience a bit of a cool
down to temperatures right at about to 5 degrees above normal,
which is generally expected to persist through the next week. The
threat of thunder has been removed from the forecast for Monday,
as the shortwave trough is now expected to move through faster,
diminishing the amount of surface heating and moisture we'd need
to generate thunderstorms.

There will be some low pressure impulses in southwest and west
flow moving through over the next week. We'll need to keep an eye
on those for possible wind increases of concern inland and over
the coastal waters, as well as variations in the extent of the
marine layer, much as we've done over the past 2 weeks.

Altogether we expect very consistent weather again from day to
day this next week, with no thunderstorm threat after today's
slight chance for the above mentioned areas. BTL

&&

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

CA...Red Flag Warning from 2 PM this afternoon to 8 PM PDT this
     evening for CAZ285.

Pacific Coastal Waters...Gale Watch from Sunday morning through
     Monday evening for PZZ356-376.
     Small Craft Advisory until 11 PM PDT Monday for PZZ356-376.

MAS/BTL/JRS