Small Craft Advisory 57, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
239 PM PDT Wed Jun 13 2018

.DISCUSSION...Aside from a smattering of cumulus here and there,
the bulk of the clouds and light showers over our area remain
relegated to the coast and the Umpqua basin. The front
responsible for this is struggling to maintain itself, and will
gradually die off as the evening progresses, leaving the rest of
the area mostly clear and dry, but also slightly cooler. While the
front will dissipate, the upper level trough is expected to hang
around, remaining firmly in place over the Pacific Northwest
through Friday morning. Until then, temperatures will remain
relatively steady at right around seasonal normals, with little
to no precipitation to speak of.

By Friday afternoon, an upper level wave will dig south from
British Columbia, reinforcing the cooler air aloft and providing
additional energy overhead. This will keep temperatures near
normal for this time of year, but will also provide the
instability and energy necessary to fire off some some showers
and afternoon thunderstorms, primarily across northern California
and along and east of the Cascades late Friday through Sunday.
Exactly where this precipitation forms, and whether or not it
makes it elsewhere, depends greatly on where the upper level low
center forms, and where it meanders. Most models consistently keep
the precipitation away from the coast and the West Side, so have
kept mention of precipitation out of there for now.

Beyond Sunday, the forecast becomes much more hazy, with models
seeming to provide a different solution every run. There is high
confidence that a slow-moving and meandering overhead low will
remain in the area, but where it wanders and whether it can
maintain its intensity remains uncertain. Given the current GFS
and ECMWF runs and their respective ensembles, there appears no
convincing reason to remove or expand the existing area of
showers and afternoon thunderstorms through the rest of the term.

As for temperatures, those same models continue to show a warming
trend Monday through next week. At the same time, this seems
inconsistent with the trough, which should maintain cooler air
aloft, and would therefore keep temperatures from rising
significantly. With this rather large source of uncertainty, have
relied heavily on analogs and local rules-of-thumb to produce the
daily highs and lows. This brings temperatures up 10 to 15 degrees
above normal for this time of year, but does not approach the
rather extreme highs suggested by the typical model outputs. This
has resulted in bit of a see-saw from the previous forecasts, but
given the constant state of change in the long term solutions,
it's not entirely unexpected. Hopefully, a more clear solution
presents itself over the next few forecast cycles. -BPN

&&

.AVIATION...For 13/18Z TAFs...IFR cigs along the coast is
quite persistent and satellite imagery shows widespread MVFR
conditions in Coos County and the coastal waters. Guidance brings
ceilings to VFR briefly this afternoon then lowers it down to MVFR
overnight. Further inland, expect widespread terrain obscuration for
the rest of today and tonight. Elsewhere, VFR but with gusty winds
this afternoon. -FB

&&

.MARINE...Updated 200 PM PDT Wednesday, 13 June 2018...North to
northwest winds are starting to increase this afternoon as a thermal
trough strengthens, and expect areas of small craft winds and seas
from Gold Beach south this evening. Winds are expecting to increase
to Gale Thursday. Areas affected for the Gale Warning extend from
just offshore out to around 50 nm and from Port Orford south, with
small craft advisory for hazardous seas from this area north to the
waters off Bandon. Gale and very hazardous seas continue through
Friday night when winds are expected to decrease below gale. Overall
conditions remain hazardous with likely small craft advisory through
next week. -FB

&&

.FIRE WEATHER...Updated 200 PM PDT Wednesday, 13 June
2018...Northwest winds will increase this afternoon and evening as
a weak front continues to push inland and weakens. Winds will be
strongest east of the Cascades where gusts to 30 mph will be
possible. Winds will diminish late this evening and overnight, and
seasonable temperatures today will continue through the weekend.

Upper level troughing will develop over the area Thursday into
Friday, becoming a cut-off low that will settle over the forecast
area through the weekend. RH's will trend lower on Thursday, before
increasing Friday and into the weekend. Winds will also trend lower
Thursday and Friday compared to today, but will still be breezy in
the afternoons.

A threat of showers and thunderstorms develops late Friday afternoon
and continues through the weekend. Model guidance is starting to
come into better agreement with this scenario, but there are still
enough differences to decrease confidence in the details. Currently,
the highest confidence in thunderstorm development is from the
Cascades eastward, both Saturday and Sunday. Confidence is lower on
the westward extent of thunderstorms, but guidance does indicate the
potential for activity along the Siskiyous and the western Cascade
foothills on Saturday. Since thunderstorms that develop will be
under a cool upper level low, we expect them to contain rainfall.

Next week, the cutoff low lingers over the area through at least
Monday and current operational runs gradually move it just east of
the area by Tuesday. Models have had a difficult time resolving this
low, and a slight westward placement of the low would continue
thunderstorm chances later into the week. This would also influence
the significant warm-up expected next week. If the low is slower to
move east, then the heat will be slower to build. So while there is
confidence that a significant warm-up will occur, there is low
confidence in the details regarding how fast the heat builds, how
hot it will get, and for how long next week. Model guidance is
consistent in indicating the warmest temperatures of the season,
thus far, mid-late next week- possibly as early as Tuesday, June
19th. BTL/BR-y

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Thursday for PZZ356-376.
     Gale Warning from 5 AM Thursday to 11 PM PDT Friday for
     PZZ356-376.

BPN/FJB/MNF