Area Forecast Discussion
Issued by NWS Medford, OR
FXUS66 KMFR 202350
Area Forecast Discussion
National Weather Service Medford OR
450 PM PDT THU OCT 20 2016
Updated AVIATION section
.DISCUSSION...20/12Z NAM/GFS/EC in.
A long wave ridge has broken to the east of the area. Southwest
flow aloft has developed ahead of the next offshore trough, which
now looks like it will remain offshore through most, if not all,
of next week. As long as it remains out there, it will send
ejected short waves at varying trajectories over the Pacific
Northwest, some of which will be fairly strong.
Initially the short waves will be relatively weak with the bulk of
the energy directed to the north of the Medford CWA. They will get
stronger with time. With an exception or two, they will take a
gradually more southerly track.
The first of these waves is now pushing a cold front onshore.
The bulk of the upper level support will remain to the north, and
the Medford CWA will only see the weak southern end of this
system. There is currently light precipitation along the coast,
over the Coast Range, and in the Umpqua Basin. This precipitation
will likely not spread much farther from where it is now, and
will continue into tonight before gradually diminishing late
tonight into Friday.
The second front will move in Friday night. This one will be fairly
dry until it moves onshore, then precipitation will begin to
develop on and ahead of the front as a short wave moves in aloft,
bringing better upper level support for the system.
Another short wave will provide better support for the next front,
which will move onshore Saturday evening. This one will likely
have some significant winds with it, especially over the coastal
waters and east side, but at this point it looks like they will
remain below gale force over the waters. The associated
precipitation will be heavier and more widespread, but not enough
to create any flooding concerns.
Still another front will follow Sunday night into Monday. This one
will be the strongest yet, with gale force winds likely over the
coastal waters. It will also be the wettest of the group, with the
heaviest precipitation centered over the usual locations in the
coast range of extreme southwest Oregon.
LONG TERM...Monday through Thursday. Not much has changed from
yesterday in the extended. The upper trough still remains the
dominate feature for first part of next week. The specific details
vary between some of the models, but all point to a wet and cool
pattern. A stronger front will bring moderate to heavy rain to the
coast and Coast Range early Monday morning. The models have come
into better agreement with the timing and progression of the
front. It`s very likely we`ll get measurable rain Monday and have
increased pops to 100 percent for most locations west of the
Cascades. Specifics on rainfall totals could vary, but the
consensus shows the highest totals along the coast and Coast Range
and Western Siksyou County. Snow levels Monday should still remain
above the major passes, but they will come down Monday night as
the front moves southeast with accumulating snow possible near and
at Crater Lake, Diamond Lake and Mt. Ashland by daybreak Tuesday.
As the front moves southeast, the focus for heavy precipitation is
expected to shift around Mount Shasta area. Meanwhile, snow levels
possibly lowering enough to affect a few of the passes like Lake
of the Woods and, possibly, Siskiyou Summit on Tuesday, but this
is still a ways out and specific details could change, so stay
tuned for the latest updates.
The upper low will weaken, but remain just offshore after Tuesday.
The models disagree with the amount of moisture being pumped into
our area. The GFS and Canadian show ample moisture moving into our
area from the southwest. The ECMWF is not as wet and has more
ridging due to a slightly stronger upper low offshore. For now
leaned towards the GFS/Canadian solution, with pops slightly above
climo. Of note, the ECMWF and GFS ensemble means are spread out
quite a bit among the individual members, especially after next
.AVIATION...21/00Z TAF CYCLE...IFR will prevail at the coast,
including at KOTH through the TAF period with some
improvememt expected after 21z Friday. Inland...VFR conditions are
expected through this evening, except MVFR/IFR will develop in the
Umpqua Valley and KRBG overnight with higher terrain partly obscured.
A front will dissipate as it moves toward the Rogue Valley
tonight. Even so, recent rainfall, a moist boundary layer, and light
winds could bring a period of MVFR CIGS/VIS briefly around
sunrise. Similarly, a period of IFR CIGS/VIS is possible at KLMT
toward daybreak. All areas except the coast will become VFR
Friday afternoon. -Spilde
Note: The ceilometer at FAA site KOTH is out of service, so there
will be no ceiling observations available generally between the
hours of 04Z and 14Z.
.MARINE...Updated 210 PM PDT Thursday, October 20, 2016...A cold
front will move onshore this evening with light rain gradually
diminishing and ending. Visibility could still be reduced at times
in fog overnight into Friday, but high pressure will build in with
lighter winds expected.
A storm over the Gulf of Alaska will generate high and steep west-
northwest swell over the coastal waters late Friday through Saturday
with an unsettled weather pattern taking shape this weekend and
continuing into at least early next week. One cold front will move
through Saturday night with gusty south winds and choppy seas.
Another stronger one Sunday night into Monday will bring the
potential for gale force winds over the entire area along with steep
to very steep wind-driven seas. Stay tuned for updates and
possible watches regarding this period of unsettled weather.
.CLIMATE...There has been good consistency in the long range
guidance in indicating normal to above normal temperatures across
the forecast area through the end of this month, when averaged
over week long intervals. Additionally, this guidance has also
been consistent, of late, in indicating near to above normal
precipitation over the forecast area for the upcoming month of
November. Temperatures look as if they will be on the cooler side
of climatology this week, and then generally near to slightly
above climatological averages for the remainder of October into
November when averaged over week long intervals. Weak La Nina
conditions in the Equatorial Pacific and a very negative Indian
Ocean Dipole are likely contributing to these expected conditions.
The net result is expected to be a continued good start to the
water year and the higher elevation mountain snowpack (above about
6kft), and removal of the last vestiges of drought designation in
our forecast area. BTL
Pacific Coastal Waters...None.