Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
541 am PST Sat Feb 6 2016
Update...see the aviation discussion below.
Aviation...for the 06/12z taf cycle...onshore flow behind the front
will bring widespread MVFR ceilings and terrain obscurations from the
Cascades west in Oregon through this morning with areas of IFR ceilings
in the Umpqua valley, including at krbg. East of the Cascades and
across northern California...expect mainly VFR conditions with areas
of MVFR ceilings possible in western Siskiyou County and into northern
Klamath County. Conditions are expected to lift to VFR at all area
terminals by early this afternoon with isolated mountain obscurations
continuing from the Cascades west through the afternoon. /Fb
Previous discussion... /issued 100 am PST Sat Feb 6 2016/
Discussion...06/00z NAM/GFS in.
The northern hemispheric pattern continues to show a near
textbook 5 wave pattern around the Globe with moderate amplitudes.
The coldest air is right is over where it should be...over
Siberia...albeit the far southeastern portion. This is normally a
The pattern will remain progressive...but will slow Sunday
through Tuesday as a strong ridge builds over the eastern Pacific
and western North America.
A long wave trough has just moved onshore with most of the energy
directed to the north of the area. The associated cold front has
been weaker than forecast...with lighter winds and less
precipitation. It is now weakening further since most of the
upper level support remains to the north. It will pretty much
dissipate against the Cascades this morning as upper level ridging
starts to build. Precipitation totals so far have been up to 0.75
inches along the coast and Coast Range...where the heaviest totals
have been. Inland totals in the Umpqua basin to the Cascades have
topped off at around a third of an inch with spotty coverage.
Totals elsewhere are less than a tenth of an inch. Snow levels
are around 6000 feet...well above pass levels...and will drop to
4000 to 5000 feet later this morning as the precipitation wanes.
The northern Cascades will see up to two inches of snow...with
small amounts over the remainder of the higher terrain.
Gusty winds are a factor over the east side...where a Wind
Advisory is in effect. However it now looks like it will barely
verify...and only around the usual windy spots like Summer Lake.
The trough will move out to the east by daybreak Saturday...and
any lingering precipitation will end by then. The aforementioned
strong ridge will then build into the area. Conditions will dry
out quickly Saturday as the upper ridge builds and low level
offshore flow develops.
The ridge will move very slowly east...amplifying through Monday.
But that time it will be directly over the Medford County Warning Area. Dry
conditions and low level offshore flow will persist through Monday
and temperatures will warm to above seasonal values...especially
along the South Coast and over the ridges. The forecast will be
more difficult over the western valleys...as the warm air aloft
will strengthen inversions over the valleys...which will tend to keep
cloud cover and cooler air trapped over those areas. Since this is
late in the season for such patterns...the low clouds and fog are
expected to burn off in the afternoons and evenings.
Usually air stagnation is a concern in a pattern like this...but
given the expected afternoon mixing...will not issue any
advisories at this time.
The ridge will continue to drift east...and weak short waves
ejecting from the upstream trough will start to move over the
area Wednesday. Typically the first short wave after a ridge has
little effect other than heralding the end of offshore low level
flow...and these look too weak to do much of anything. More short
waves will follow though...pushing progressively stronger fronts
onshore. So...precipitation will likely return sometime in the
second half of next week. The best guess for the next significant
round of precipitation right now is next Thursday night.
Aviation...for the 06/06z taf cycle...a front moving inland
tonight and weakening over the area Saturday will bring widespread
MVFR ceilings and terrain obscurations from the Cascades west in Oregon
tonight through Saturday morning. Areas of IFR ceilings are also
expected to develop late tonight and continue Saturday morning in
the Umpqua valley, including at krbg. Along the coast, expect a mix
of MVFR and IFR ceilings tonight into Saturday morning. East of the
Cascades and across northern California...expect mainly VFR
conditions with areas of MVFR ceilings possible in western Siskiyou
County and into northern Klamath County. Conditions are expected to
lift to VFR at all area terminals by early Saturday afternoon with
isolated mountain obscurations continuing from the Cascades west
through the afternoon. /Cc
Marine...updated 950 PM PST Friday Feb 5 2016...behind a
front...expect steep seas to continue tonight into Saturday with
seas dominated by westerly swell. Winds will become light tonight
then a light east to southeast flow will develop on Saturday as high
pressure builds into the area. Sunday and Monday...expect light
east to northeast winds...with winds becoming southerly on Tuesday
as high pressure shifts inland. Additional...steep swell will enter
the waters Monday and Tuesday. A front may near the coastal waters
middle week then move into the waters Thursday into Friday with
additional steep seas. /Cc
Pacific coastal waters...Small Craft Advisory for hazardous seas until 5 PM PST this
afternoon for pzz350-356-370-376.