Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
445 am PDT Friday Oct 28 2016
Aviation...29/12z taf cycle...low clouds and fog continue to
affect inland west side valleys this morning and conditions will
likely remain IFR or worse until mid morning. Thick high cloud is
moving across the east side and disrupting fog formation there.
Conditions are generally MVFR but may be locally down to IFR in
fog until just after dawn. A weak front has moved into the coast
and is providing enough mixing to limit fog there as well.
However, MVFR conditions with some showers can be expected.
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.
Previous discussion... /issued 337 am PDT Friday Oct 28 2016/
Discussion...although there is generally good agreement in the
mid level pattern between the operational models, there is a far
greater spread of solutions when it comes to the surface fields.
The spread in solutions only gets worse as we head through the
weekend and into next week. That being said, there is high
confidence in a generally wet and active pattern, but forecast
confidence is much lower in regards to the details of timing and
strength of each individual feature.
Currently, the jet stream remains draped across central
California, well to our south. Radar imagery shows a broad swath
of precipitation spreading from San Francisco through Nevada, but
no returns currently within our forecast area, mainly as a result
of smaller scale ridging between the trough to our west and the
wave to the southeast. Meanwhile, fog has developed in many of the
area valleys, and there is no reason to think it will dissipate
until later this morning.
The next shortwave associated with the large trough to the west
will make its approach to our area tonight. This will produce
another round of widespread precipitation, especially along and
ahead of the front as it pushes through in the overnight and early
morning hours. Showers will then continue through Saturday before
the next wave slides through Sunday, brining even more rain.
Overall, this will be a wet weekend across the area. While
rainfall amounts will be appreciable, especially when seen on top
of this already very wet October, they will not be enough to
create any hydrological problems. We do expect an additional 2-3
inches of water to fall in The Mount Shasta area and 0.50 to 1.5
inches for much of the rest of the area, greatest in south and
southwest flow favored areas. Saturday morning through Monday snow
levels are also expected to fall to between 5500 and 6500 feet, so
there will be a rebuilding of the snowpack where we have lost some
and a further increase on the peaks of the Cascades.
The wet weather will continue on into Halloween, as yet another
wave pushes onshore during the afternoon and evening.
Unfortunately for those trying to stay dry during any festivities,
the models show the heaviest precipitation passing through the
area right around sunset. As mentioned above, confidence is low in
the exact timing, so stay tuned for forecast updates over the next
Beyond Monday, there is little forecast confidence, but there are
some hints to another stronger frontal passage Wednesday night,
then again on Friday. Given the uncertainty and the wide range of
model solutions, have opted not to try and nail down the timing of
any particular event, but instead kept precipitation chances
during the long term at or slightly above average for this time of
Marine...updated 300 am PDT Friday, October 28, 2016...a weak
front will dissipate over the waters this morning, then weak high
pressure builds in this afternoon through tonight. Winds and seas
will continue to diminish as a result. A long period west swell
will arrive and south winds will increase on Saturday as low
pressure approaches. This area of low pressure moves over US
Sunday with elevated seas and variable winds that will likely be
hazardous to small craft.
Another closed low pressure system will likely move south of the
waters and into California Monday into Tuesday with the next strong
front arriving Tuesday night into Wednesday. This front will have
the potential to bring gales and very steep hazardous seas. All
guidance continues to show this scenario, so confidence is
Pacific coastal waters...none.