Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 271624

Area Forecast Discussion
National Weather Service Medford OR
924 AM PDT Tue Jun 27 2017

.DISCUSSION...The main feature this morning is the fairly deep
marine layer that has produced a low overcast over all of Douglas
county except for the eastern portion where the Cascades rise
above the clouds. The marine layer got over the Umpqua divide and
worked its way down the valleys in Josephine county. Model
boundary layer RH charts depict this quite well. Models depict a
similar scenario tomorrow morning and then a bit less of a push
Thursday morning. Will take these things into consideration for
the afternoon forecast package in terms of sky cover.

One other thing going on is a wee bit of instability this
afternoon near Mount Shasta in Siskiyou County as a very weak
disturbance moves through this afternoon. This is already in the
forecast so will let it ride.


IFR and MVFR ceilings and visibilities extend across the coastal
waters, across the coastal counties, and into much of Douglas and
Josephine counties. Patchy fog is also present at and around KLMT.
Expect fog at KLMT to dissipate quickly this morning while,
elsewhere, it`s likely to take until early afternoon to dissipate.
There is slight threat of the thunderstorms late this afternoon into
this evening across Siskiyou county. IFR and MVFR are expected to
return across Coos and Douglas tomorrow morning. BTL


.MARINE...Updated 300 AM Tuesday, 27 June 2017...
North winds will increase and seas will steepen today through
Wednesday evening as high pressure rebuilds offshore and the thermal
trough deepens over California. Warning level seas are expected to
develop over a portion of the area south of Cape Sebastian Wednesday
into Thursday. Northerly gales are possible south of Cape Blanco
this weekend as cooler air pushes southeastward from the Gulf of
Alaska. BTL


.FIRE WEATHER...Updated 6 AM PDT Tuesday, 27 June 2017...
An extensive marine layer spread across most of Douglas County and
into Josephine County from the coast is likely to take until late
morning to early afternoon to dissipate. Lingering moisture and
instability combined with a weak impulse aloft will result in a
slight chance of thunderstorms across portions of Siskiyou County
late this afternoon into early this evening. Thereafter,
temperatures are expected to remain 5 to 10 degrees above normal,
with the warmest temperatures likely to occur this weekend. BTL


.PREV DISCUSSION... /Issued 630 AM PDT Tue Jun 27 2017/

DISCUSSION...Current radar scans are showing that the
thunderstorm threat has dissipated completely. This signals the
switch in the overall pattern from a strong ridge and thermal
trough which brought us record or near record temperatures over
the weekend to a more typical end of June pattern.

Meanwhile, current satellite composite imagery is showing a
relatively strong marine layer occurring along the coast which has
already pushed into the Umpqua basin past the Umpqua divide into
Josephine County. At this rate, the marine layer could bring some
clouds all the way to Grants Pass before the night concludes and
the marine layer breaks up and moves back out to sea this morning.
With this marine layer, extremely light drizzle will be possible
along the coast. At this point, the drizzle is not expected to
produce measurable precipitation. Tomorrow evening and overnight,
however, the marine layer will come back; and the NAM and GFS are
indicating that some more light drizzle will be possible across
the coast and coastal mountains. This drizzle, although light,
could produce measurable precipitation; and have introduced a 10%
chance for it in a swath from a few miles south of Port Orford
northeast to the Douglas and Lane County border.

Elsewhere around southern Oregon and northern California, the
water vapor and infrared satellite imagery suggests that the
clouds have moved out of our area and clear skies remain. The
forecast today will include a slight chance for showers and
thunderstorms this afternoon across portions of Siskiyou County.
The Moisture profiles are expected to be somewhat less than they
were the last two days which could very well be the limiting
factor for the Cascades and the Siskiyous. As a result, have
dropped the mention of thunderstorms over the Cascades and
Siskiyous from the previous forecast. A few models want to
produce a few showers and storms in Lake County. Although moisture
will be somewhat higher than over the Cascades, the lifted
indices and instability look to be stronger over the Cascades
instead of Lake County and this may be the limiting factor there.
Have left the mention of showers and storms out of the forecast
from Lake County for now.

Beyond tomorrow, the forecast calls for drier weather and normal
temperatures across the board as our next ridge builds into place.
Although this could allow for the next thermal trough to build,
models are showing relatively stable 850 millibar temperatures
and have kept the forecast quite similar to the previous forecast
with only slight changes with a slight favoring toward the GFS
here and there. -Schaaf




Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Thursday for PZZ356-376.
     Hazardous Seas Watch from Wednesday morning through Thursday
     morning for PZZ356-376.
     Small Craft Advisory for hazardous seas from 11 PM this evening
     to 11 AM PDT Thursday for PZZ350-370.


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