Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 222142
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
242 PM PDT Mon Oct 22 2018

.SHORT TERM...Satellite imagery this afternoon is showing a
persistent marine layer over the coastal waters and along the
immediate coast. This is bringing stratus to the beaches and about
5-10 miles inland into Douglas and Coos Counties (except to about
Coquille/Myrtle Point in Coos County). Some stratus also extends
into the river valleys south of Cape Blanco, up to about 5 miles
up river. Marine layer clouds, some fog and perhaps a little
drizzle will affect these same areas tonight. Inland, it is mostly
sunny this afternoon, though some high clouds/cumulus have
developed across the far east side. Expect these clouds to
dissipate this evening with a mainly clear sky in these areas
overnight.

Meanwhile, the high that has been so dominant over the area for
the last week or so is weakening. This will allow a frontal
system to approach the area and move onshore Tuesday. Models have
been fairly consistent showing that this front will bring clouds
and some rain to the coast (0.10-0.20" on average), but upper
level support will fizzle and so will the front as it pushes
inland. As a result, we expect little, if any, precipitation to
make it south and east of the mountains. It may be enough for just
a few drips here in Medford late Tuesday afternoon/evening, but
that`s about it. While coastal areas probably have temperatures
similar to today, all inland areas will be about 5-10 degrees
cooler Tuesday due to increasing cloud-cover and general lowering
of temperatures aloft.

Late Tuesday night through Wednesday night, weak short-wave
ridging will build in, so we`re not expecting any precipitation,
though there`ll likely be some lower clouds and fog west of the
Cascades.

Our next chance of rain will come from midday Thursday through
Thursday night as a short wave impulse rides over the top of a
building upper ridge off the California coast. Once again,
however, the main jet axis will be directed to the north of the
area. Models continue to trend northward with precipitation, so we
have adjusted the forecast accordingly, with the best rain
chances expected across the NW sections of the area. Precipitation
will again be hard-pressed to make it as far south and east as
Medford and probably won`t reach northern California. -Spilde

.LONG TERM...Friday 26 Oct to Monday 29 Oct...The second sacrificial
front brushes the northwestern portion of the forecast area with
some rainfall Friday, but most areas will remain dry as ridging
builds quickly behind the front. To give an idea on how little this
front impacts the area, surface temperatures are expected to rise on
Friday as the upper ridging builds.

Temperatures rise further on Saturday, and there is high confidence
in dry weather for the entire forecast area on Saturday. All GEFS
members are void of precipitation for the forecast area on Saturday,
and we are forecasting high temperatures of 15 degrees above normal
for Saturday afternoon. We won`t be surprised if we manage to hit 80
degrees in a few West Side valleys Saturday afternoon. In contrast,
we will be very surprised if we see 80 degree temperatures after the
weekend given how rare it is to observe 80 degrees in West Side
valleys in late October (and very rare in November).

Operational models show another chance for rain Sunday, but
confidence is low for rainfall at this point, given the recent
"overforecasting" of rainfall by the models. This is especially the
case given the building ridge on Saturday, and the fact that GEFS
median QPF is zero on Sunday even for the coast. Another tool in the
toolbox, the CFSV2 model, suggests dry conditions in week 2 for its
latest run (initializing on 21 Oct). Monday we continue to feature
slight chance of precipitation for most areas under weak upper
troughing per the GFS and EC operational models. Even though we`re
not confidence in rain chances Sunday and Monday, we are more
confident in daytime temperatures lowering to closer to normal for
this time of year. -Keene

&&

.AVIATION...For the 22/18Z TAFs...Along the coast and marine waters,
LIFR cigs and fog continue, and the main question is whether there
will be much improvement. At best, some areas may improve to IFR
briefly this afternoon, only to come back down tonight. A front
moving in tomorrow will bring will bring increased winds and
improved mixing, so cigs may be a bit higher. As with the last
several mornings, expect some patchy fog in the Umpqua Basin, but it
may not be enough to bring KRBG down a category. Elsewhere, VFR
expected for the whole TAF period, save for potential lower vsby in
smoke near the Klondike Fire and any prescribed burns.

&&

.MARINE...Updated 200 PM PDT Monday 22 October 2018....Northwesterly
swell dominated seas will persist today. Winds will turn
southerly tonight ahead of the first in a series of fronts. Winds
and seas with this first front will make for small craft advisory
conditions Tuesday. The next front will move in Thursday, and it
will bring another round of increased southerly winds as well as
possible steep west swell. Winds and seas will diminish Friday
into Saturday as high pressure moves through, then another front
will move in Sunday.

&&

.FIRE WEATHER...Updated 220 PM PDT Monday, 22 October 2018...
Tonight should be the last in a stretch of upper slope and
ridgetop poor to moderate humidity recoveries. Inland highs will
cool by 5 to 10 degrees Tuesday as a front moves through, and
humidity will increase significantly from the Cascades westward.
Humidity will slightly increase east of the Cascades. Southerly to
southwesterly winds will increase across the mountains, northern
California, and the east side on Tuesday. We are forecasting
particularly gusty winds in the Shasta Valley Tuesday afternoon.
Also, for areas west of the Cascades, areas may feel a period of
south to southeast winds Tuesday ahead of the front that haven`t
seen much south wind recently. The weakening front on Tuesday will
bring rain mainly from the Coast Range and Umpqua Divide
westward. Another front is expected to affect mostly the same
areas with some rain Thursday into Friday. Wetting rain amounts
are not expected with either front for most areas.

Wetter conditions are now expected to arrive between the 29th and
31st per the operational GFS and ECMWF. The typically more reliable
GEFS mean is suggesting significant wetting rains arriving Oct 31st -
 Nov 1st. Of course, models keep trending back the timing of the
wetness with each model cycle in recent days, so we`ll see if that
trend continues. Keene/Lutz

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory from 8 AM to 11 PM PDT
     Tuesday for PZZ350-356-370-376.

$$

MAS/MSM/NSK


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