Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 221616
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
916 AM PDT Mon Jul 22 2019

.DISCUSSION...
No updates are necessary this morning.

A fragmented marine layer exists across portions of Coos and
Douglas counties this morning as well as south of Gold Beach
along the Curry County coast. This is gradually dissipating, as
expected.

Meanwhile some convergence and instability related cloudiness is
present along and near the Cascades and across far southeastern
portions of the forecast area.

Yesterday the National Lightning Detection Network indicates we
had 67 cloud to ground lightning strikes in Fire Weather Zone
625 / 96 CG strikes in Lake County. No CG lightning was observed
outside of that area in our forecast area.

Today thunderstorm potential is greatest from the High Cascades
north of Highway 140 eastward across northern Klamath and Lake
counties. There is a lesser risk of lightning from just north of
the Trinity Alps in the Scott Mountains northward into the
Siskiyous at and around Mount Ashland, as well as over eastern
Lake and far northeastern Modoc counties in the Warner Mountains.
Once again, thunderstorms today will produce little or no rainfall
where they do occur, so fire starts are possible. However,
thunderstorm coverage will be isolated, so strikes should be
limited, likely under 100 CG strikes for our CWA, and likely
lesser in our Fire Weather Zones (which don`t extend as far north.

Winds pick up Tuesday afternoon and evening across the east side
and there will be a lingering threat of some lightning which will
be discussed further in this afternoon`s discussion. BTL

&&

.AVIATION...For the 22/12Z TAFS...Along the coast and over the
coastal waters...Areas of MVFR/IFR ceilings with patchy fog along
the coast north of Cape Blanco and south of Gold Beach will clear
to VFR by Monday afternoon. The lower conditions will redevelop
Monday evening and persist into Tuesday morning. Over the remainder
of the area...VFR conditions will persist into Tuesday morning, but
there will be isolated afternoon and evening thunderstorms mainly
from the Cascades north of Crater Lake across northern
Klamath/Lake Counties, Winter Rim to the Warner Mountains eastward,
and over western Siskiyou county. These will likely stay clear of
the TAF sites.

&&

.MARINE...Updated 230 AM PDT Monday 22 July 2019...Winds and seas
will diminish tonight into Monday and will remain below advisory
levels into Tuesday morning. The thermal trough will restrengthen
beginning Tuesday, and this will bring stronger north winds and
choppy wind driven seas back to the area, especially south of Cape
Blanco. Winds may reach gale force Wednesday afternoon through
Thursday night south of Cape Blanco.

The thermal trough will weaken Friday into Saturday, then ramp up
again Saturday night through Monday night.

&&

.FIRE WEATHER...Updated 200 PM PDT Sunday 21 July 2019...Cumulus
clouds are slowly starting to develop east of the Cascades.  We`re
still expecting isolated thunderstorms in Lake, Klamath and Modoc
Counties this evening.  There is also a slight chance for
thunderstorms near the Sikiyou horn near fire weather zone 280.
Isolated thunderstorms will persist overnight in Lake and Modoc
counties, but the activity should be on the down trend.

Thunderstorm activity will redevelop again on Monday afternoon.
Again, isolated thunderstorms are the main threat in the same areas
mentioned in the above paragraph.  However, some of the storms may
shift a bit farther west into the Cascade Range north of Crater
Lake.

Winds and RH then become the focus on Tuesday.  We`re expecting
winds to pick up ahead of the trough with a fair amount of dry air
moving into areas east of the Cascades.  It looks like RH`s will
rise on the westside on Tuesday, yet conditions will still remain
dry on the eastside.  With fire danger starting to shift into the
high thresholds,  we felt a fire weather watch was appropriate on
Tuesday afternoon, especially with the lightning activity occuring
this evening and again Monday.

There is some uncertainty with the RH forecast on Tuesday as cloud
cover could inhibit RH`s dropping low enough to verify a red flag
warning. However, we have high confidence the winds will be critical
Tuesday afternoon. -Smith

&&

.PREV DISCUSSION... /Issued 440 AM PDT Mon Jul 22 2019/

DISCUSSION...Isolated thunderstorms brought a good number of in
cloud flashes yesterday afternoon into the evening, but many less
strikes that hit the ground, mostly in eastern Lake County. With
moisture continuing to feed into the region today and with
southerly flow now feeding in down to the BL as well as the ridge
tops, have more confidence for thunderstorms to develop east of
the Cascades this afternoon. Instability is indicated from the
Cascades in the Crater lake area to the southeast into Lake
county. However, mid level moisture is weak over the Cascades, and
the most likely chances of isolated thunderstorms should be to the
east of the Cascades. There is no "kicker" moving through and with
this weak instability will keep thunderstorms as isolated in this
area. In western Siskiyou county there was some vertical
development, but nothing high enough to develop into a
thunderstorm. There is increased column moisture today, but
instablity is marginal so have gone with "slight chance" wording
as confidence is not high that anything will develop in that
area.

As we head into Tuesday the ridge top winds increase to 15 to 25
kt. The area of instability shifts to the north and east with weak
instability from the Crater Lake area to the northeast. With the
strong 700 mb flow there is only a slight chance that anything
that does develop will put anything down before being pushed to
the northeast out of the forecast area.

The upper low will open and move east through vancouver Island
Wednesday morning, with the resulting more westerly flow shifting
instability out of the region. -Sven

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Tuesday afternoon through Tuesday
     evening above 500 feet in the for ORZ624.

CA...Fire Weather Watch from Tuesday afternoon through Tuesday
     evening below 500 feet in the for CAZ285.

Pacific Coastal Waters...
- Small Craft Advisory from 11 AM to 5 PM PDT Tuesday for
  PZZ356-376.


$$

BTL/SBN/CZS


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