Area Forecast Discussion
Issued by NWS Medford, OR

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864
FXUS66 KMFR 300250
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
730 PM PDT MON AUG 29 2016

.Updated aviation and marine discussion.

.DISCUSSION...A red flag warning remains in effect for much of the
east side this evening for gusty winds and low humidity. It will
be cooler on Tuesday, but another day of gusty east side winds and
low humidity is expected.

A swath of upper level clouds is pushing east to northeast and
currently is in place near the Cascades and across the east side.
There is also a gusty south to southwest flow aloft that is
emanating from the Gap wildfire in the Seiad Valley and has
continued smoky conditions across the Siskiyous into Jackson
County. The amount of smoke in the Rogue Valley will vary based
upon fire behavior and fire fighting efforts, but southwest winds
aloft will persist and limit improvement of air quality into
Friday. The upper level clouds will thin this evening but the
shortwave trough offshore from northern California is moving
rapidly to the northeast. The model consensus has sped up the
timing of this shortwave by a few hours. As a result, the
probability of showers over the higher terrain on Tuesday morning
has been increased from southwest Siskiyou County across the
southern Oregon Cascades. The timing of a morning passage with
less heating than in the afternoon will hinder thunderstorm
development, but the fast movement of about 30 KT does mean that
any storms that do form will produce little if any rainfall. The
highest probability of a thunderstorm will be in northern Klamath
County during the mid and late morning on Tuesday. The main risk
will shift into north central Oregon by the afternoon.

Beyond Tuesday afternoon through Friday, a broad and slow moving
upper level trough will track from the Gulf of Alaska into the
Pacific Northwest. It will send a series of disturbances brushing
past our area to the north and continue an onshore flow at the
coast with frequent low clouds. Fog will not be as dense as during
the past few days with some lifting as systems pass through.

There will be two main systems. First, a cold front whose weaker
southern fringe will move across our area on Wednesday with a
chance of light showers for the coast into the Umpqua Valley.
Model agreement diminishes on Thursday. The GFS is a bit stronger
and colder than the ECMWF regarding the next disturbance that will
follow a similar path with similar or slightly stronger strength
on Thursday night into Friday morning. Rainfall once again looks
to remain north of the Umpqua divide. The main effect of the model
difference would be whether our coast receives very light rain or
a wetting rain of about a quarter of an inch.

The main upper trough will swing across the Pacific Northwest
Thursday night through Friday. A shortwave on the backside of
the trough will continue a slight chance of showers north of the
Umpqua Divide into Friday evening.

Picking the coolest day of the week is a bit tricky. The coolest
of the days may vary based on location. The greater amounts of
cloud cover in southwest Oregon will limit heating through mid-
week. Clouds look to diminish into the weekend but a cool
northerly flow is expected behind the trough on Saturday. There is
general model agreement that ridging over the eastern pacific will
bring a warming trend early next week.

&&

.AVIATION...30/00Z TAF cycle...Along the coast
and over the coastal waters...widespread MVFR/IFR cigs will persist
through Tuesday morning. Inland...VFR conditions will prevail
through Tuesday morning with two exceptions. The marine layer per
the North Bend profiler has deepened sufficiently so MVFR/IFR cigs
will spread into the Umpqua Basin as far as the KRBG area late
tonight through mid-morning Tuesday. Also...areas of reduced
visibilities in smoke and haze from the Gap fire over northwest
Siskiyou county will persist through Friday morning and beyond. The
greatest impact from the smoke will be over Western
Siskiyou...Josephine...and Jackson counties. SK

&&

.MARINE...Updated 300 PM PDT Monday 29 August 2016...A quiet pattern
is expected for most of the week. Light to moderate south winds will
continue through Wednesday ahead of a front which will move onshore
late Wednesday.  Conditions will remain below Small Craft Advisory
criteria. More weak fronts will follow Thursday through Friday, but
none of them are expected to bring small craft conditions. Small
craft conditions will return next Saturday at the earliest. SK

&&

.FIRE WEATHER...Updated 100 PM PDT Monday 28 August 2016...The
main concern this afternoon and evening and tomorrow afternoon and
evening is gusty winds combined with low relative humidities...
mainly east of the Cascades. A red flag warning remains in
effect from 12 pm until 8 pm pdt today for these conditions. At this
time...it looks like it will remain windy and dry Tuesday afternoon
and evening...with the critical area displaced farther east into
eastern Lake county.

Another concern is thunderstorms.  A short wave moving up from the
southwest will bring the possibility of convection to Siskiyou county
late tonight and into the northern Cascade and northern Klamath/Lake
counties Tuesday afternoon.  At this time it looks like that surface
heating will be required to fuel thunderstorms...so the current
forecast goes for showers over Siskiyou county Tuesday morning and
thunderstorms farther north and east in the afternoon. The wave will
move out to the northeast Tuesday evening...taking the thunderstorms
with it. -JRS

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 9 PM PDT this evening for ORZ624-625.
     Red Flag Warning from 2 PM to 8 PM PDT Tuesday for ORZ624-625.

CA...Red Flag Warning until 9 PM PDT this evening for CAZ285.
     Red Flag Warning from 2 PM to 8 PM PDT Tuesday for CAZ285.

Pacific Coastal Waters...None.

$$

DW/JRS/NSK



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