Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 301558
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
858 AM PDT TUE AUG 30 2016

.DISCUSSION...A few light sprinkles/showers are out there this
morning, mainly from southern Siskiyou County northward to the
Cascades. But, most of these won`t last more than a few minutes in
any one location and likely will not produce any measurable
rainfall. These are being caused by an upper level short wave that
is moving through northern California this morning. This short
wave will move quickly through Klamath and Lake Counties by this
afternoon, with just a slight chance of a thunderstorm from near
Crater Lake east and north. Anything that does develop will
quickly be carried off to the northeast by mid-late afternoon. The
air mass aloft dries out rapidly above 600mb by 00z (5pm PDT), so
that should end any lightning risk. We should still see some gusty
breezes kick up this afternoon and evening in the Shasta Valley,
NE California and east of the Cascades. Low RH values down near 10
percent are likely over the east side.

Smoke from the Gap Fire has lifted overnight into this morning,
but has also been displaced a bit to the east from where the main
plume was yesterday. Model mid level winds indicate they may back
a little to the south again this afternoon, which could carry some
of the smoke over the south end of the valley during this time
frame, but low-level flow becomes northwesterly and the mid-level
flow returns to southwesterly tonight, so this should push it
southeast of the valley by Wednesday morning. Heading into late
week, the upper trough off the PacNW coast will move closer and
winds will become westerly enough to keep the smoke at bay. This
flow pattern should persist into the Labor Day weekend, keeping
the smoke east or south of the Rogue Valley.

Overall, we`ll have temperatures about 5-10 degrees below normal
today through Saturday. Several short waves will rotate through
the area during this time frame with showers primarily from the
Cascades and the Umpqua Divide north and west. A stronger
disturbance may bring showers a bit farther south and east
Thursday night into Friday. -Spilde

&&

.AVIATION...30/12Z TAF cycle...The marine layer continues it`s push
inland with scattered to broken clouds 10 thousand feet above ground
level or higher in the region.  Moving through the day, the typical
coastal deck will persist with weak onshore flow during Tuesday. So
North Bend and coastal regions will be under IFR conditions this
morning before lifting to MVFR in the afternoon.  The other wild
card will be smoke from the Gap fire.  Flow aloft will continue to
push smoke towards MFR,  so brief reductions in visibility are
possible this afternoon if enough smoke pools in the Rogue Valley.
Did not put smoke in the MFR TAF as uncertainty is high at this
point. -Smith

&&

.MARINE...Updated 300 AM PDT Tuesday 30 August 2016...Light to
moderate south winds will continue through Wednesday ahead of a
front. This front will move onshore Wednesday afternoon.  Another
weak frontal system will follow Thursday through Friday. Conditions
will remain below Small Craft Advisory criteria through Friday.
Small craft conditions are expected to return next Saturday and
Sunday as gusty north winds and areas of steep seas develop, mainly
for portions of the waters from Cape Blanco southward. -CC

&&

.FIRE WEATHER...Updated 840 AM PDT Tuesday 30 August 2016...The
main concern this afternoon and evening is gusty winds combined
with low relative humidities east of the Cascades. A red flag
warning remains in effect for zones 624, 625 and 285 from 2 pm
until 8 pm pdt today for these conditions.

Another concern is thunderstorms. A short wave disturbance moving
up from the southwest will bring a slight chance for light showers
to Siskiyou county and to the Southern Oregon Cascades near Crater
Lake and northeast into Northern Klamath County this morning.
There is a slight chance for a thunderstorm late this morning into
the afternoon from the Southern Oregon Cascades near Crater Lake
northeastward into Klamath and Lake counties. The disturbance will
move out to the northeast this evening...with lightning risk
ending quickly. -CC/Spilde

&&

.PREV DISCUSSION... /Issued 400 AM PDT TUE AUG 30 2016/

DISCUSSION...Currently, radar imagery shows some light
precipitation, likely not making it to the ground, sliding north
into our area from northern California. These are likely the
result of a short wave within the upper level flow, orbiting the
large closed low just offshore of British Columbia. These showers,
with the addition of some daytime heating this morning and
afternoon, could strengthen, and while some light rain is all that
is expected, a rumble of thunder is not out of the question for
the Cascades and portions of the East Side. Not likely, but
possible. For the most part, the area will remain dry, cooler, and
breezy through this evening.

The trough will dig south through the week, and the main axis is
expected to finally pass overhead Friday morning. Until then,
waves of energy moving along the periphery of the trough will pass
overhead, each bringing slight chances of showers, mainly to the
coast, the Umpqua basin, and the Cascades. During this time,
temperatures will steadily cool, and by Thursday and Friday, highs
will be around 5 to 10 degrees below normal for this time of year.

This weekend and early next week, much depends on the movement of
the trough, most likely stalled out just to our east, and
subsequent reinforcing waves within the northwest flow over our
region. Models don`t have a clear consensus on the answer, but
generally speaking, the region should remain within cyclonic flow
aloft, and there will be an ongoing threat of light showers, but
little else. As there is little to no confidence in any given
wave, have not made mention of precipitation in the forecast
beyond Friday, but given the pattern, temperatures should stay
near or slightly below normal through the remainder of the term.

AVIATION...30/06Z 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. Sven

MARINE...Updated 300 AM PDT Tuesday 30 August 2016...Light to
moderate south winds will continue through Wednesday ahead of a
front. This front will move onshore Wednesday afternoon. Another
weak frontal system will follow Thursday through Friday.
Conditions will remain below Small Craft Advisory criteria through
Friday. Small craft conditions are expected to return next
Saturday and Sunday as gusty north winds and areas of steep seas
develop, mainly for portions of the waters from Cape Blanco
southward. -CC

FIRE WEATHER...Updated 400 AM PDT Tuesday 30 August 2016...The
main concern this afternoon and evening is gusty winds combined
with low relative humidities east of the Cascades. A red flag
warning remains in effect for zones 624, 625 and 285 from 2 pm
until 8 pm pdt today for these conditions.

Another concern is thunderstorms. A short wave disturbance moving
up from the southwest will bring a slight chance for thunderstorms
to Western Siskiyou county and to the Southern Oregon Cascades and
northeast into Northern Klamath County this morning. Although the
chance for storms is not high this morning, cannot rule out a
thunderstorm or two in these areas. The slight chance for
thunderstorms expands slightly in the afternoon from the Southern
Oregon Cascades eastward into Klamath and Lake counties. The
disturbance will move out to the northeast this evening...with
thunderstorm chances diminishing. -CC

&&

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

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

Pacific Coastal Waters...None.

$$

MAS/MAS/MAS



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