Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
327 PM PDT Thursday Oct 27 2016
Short term...through Monday...
a jet streak moving through the area from the south-southwest
late this morning into early this afternoon briefly crashed snow
levels from the 7-8kft range down to near 5kft. A couple of
inches of snow fell in those areas above 5kft in a short period
of time. Temperatures have since warmed several degrees in the
mountains and precipitation rates have greatly diminished, so
additional accumulations are now confined to elevations above
about 6500 feet. Winds are also winding down in the mountains, and
we might be able to end the Wind Advisory in effect for portions
of the east side early if current trends continue.
Rainfall in the last 12 hours has been fairly impressive, with
most areas between the Coast Range and the Cascades getting a half
inch to an inch and a half of water. For many areas in our
forecast area this has already been the wettest October since
1962! With upper level support for precipitation shifting
eastward, precipitation rates are diminishing, and will continue
to through tonight from the Cascades westward. By morning
extensive low clouds and fog are expected across the valleys from
the coast to the upper Klamath and Sprague River basins south to
The Mount Shasta and MC Cloud area. Some rain will continue with
the remnants of the front east of there.
Friday is expected to be precipitation free north and west of
about Klamath Falls and east of the Coast Range as mesoscale high
pressure overspreads most of the interior. Elsewhere, the front
will wave back westward over and near northeastern California. Fog
could linger in the valleys of the interior into the afternoon.
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 7-14 day outlook also looks wet and may very well be wetter
than even the next 7 days. Btl
Long term...Monday through Thursday night.
There is less confidence in the extended forecast from today's run
than yesterday's. Both the European model (ecmwf) and the GFS are still forecasting a
split jet with a closed low in the southern stream that is forecast
to come inland over north-central California around Monday night.
The European model (ecmwf) brings the trough farther north thus affecting both of our
southern Oregon zone and northern California zone, whereas the GFS
allows southern Oregon to be affected by the northern branch of the
jet. Confidence is moderate that we will see precipitation on Mon
but the GFS solution will bring colder air into the area, and more
snow at Crater Lake and Mount Ashland area.
By Tuesday, the next broad cold trough is expected to move into
the Gulf of Alaska. This allows ridging downstream into the West
Coast. Confidence however is not very high on this scenario as
models often moves a closed low out too quickly. Therefore we
continue to maintain chance probability of precipitation in the forecast for Tuesday.
Wednesday and Thursday could be relatively warm days as 500mb
heights rise and southerly flow increases ahead of the next system.
While there is a chance of rain in the forecast, confidence in
measurable rain is not very high and precipitation could be more
showery on Thursday. /Fb
Aviation...28/18z taf cycle...rain will be widespread across
southern Oregon and northern California with terrain and mountains
obscured during until this evening. Expect areas of MVFR cigs with
local IFR cigs especially near mountains. Sky is expected to clear
late this evening as the front moves farther east. The clearing will
allow radiational cooling to bring fog and low clouds to the area
with periods of IFR cigs possible for inland taf locations around
East of the Cascades, short term model indicates the strongest
energy from the storm will keep moderate to heavy rain at klmt until
22z this afternoon with MVFR cigs for the remainder of the day.
Heavier showers could bring ceilings temporarily down to IFR.
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 200 PM PDT Thursday, October 27, 2016...
seas will continue to lower this afternoon and tonight but will
remain steep and hazardous to small craft. The strongest winds are
expected beyond 10 nm from shore north of Cape Blanco. Conditions
should improve briefly Friday when south winds subside to 10 kt or
less. A long period west swell will arrive Saturday morning and
persist through the day, and south winds will increase on Saturday
as well. A broad area of low pressure will move through the waters
Saturday night into Sunday.
Model guidance has come better in line with respect to next week.
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, but
given the active pattern, confidence in this scenario is low at this
or...Wind Advisory until 8 PM PDT this evening for orz029>031.
California...Wind Advisory until 8 PM PDT this evening for caz083-085.
Pacific coastal waters...
- Small Craft Advisory for hazardous seas until 5 am PDT Friday
- Small Craft Advisory until 5 am PDT Friday for pzz370.