Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
253 am PST Sat Dec 3 2016
Discussion...a weak cold front will settle in across the far
northern part of our forecast area today and become stationary.
There is really no dynamics associated with the front, so today
ought to be precipitation-free with cloudy to partly sunny skies
and normal temperatures.
A much stronger cold front drops in from the north Sunday,
spreading valley rain and mountain snow across much of the area
through the day. Snow levels will rise a little bit to around 5500
to 6000 feet before the front passes, but then plummet Sunday
night as colder air pours in. The Cascades are on track to get a
foot or more of snow with the system Sunday, and this includes
Crater Lake. Since this snow is pretty evenly spread out over an
18 hour period, it probably won't reach warning criteria. However,
these amounts will be well within advisory criteria, but we'll
give it another model run before making that decision.
Snow levels drop to around 1000 feet by Monday morning, but
precipitation will be ending, so snow impacts for lower elevations
do not look likely. However, the upper trough will bring another
batch of precipitation Monday afternoon through Tuesday morning.
Since precipitation starts during the day, snow levels will be
probably be just high enough to not have impacts in the valleys
Monday afternoon. However, the passes along i5 north of Grants
Pass may be impacted, especially as night falls. Snow levels will
fall close to the valley floors again Monday night into Tuesday.
Models remain consistent with the magnitude of the cold air, but
they have backed off a little on the amounts of precipitation and
now show little more than an inch or two down to 1000 feet and
maybe 2 to 4 inches in the mountains. Still, it doesn't take much
snow to cause problems over lower elevations, so residents and
travelers should keep an eye on the forecasts for Monday night and
Tuesday as low elevation snow remains possible.
Precipitation tapers off and skies clear later Tuesday which will
set the stage for the coldest night of the season Tuesday night.
It looks dry and chilly through Wednesday, then a warm front will
bring more precipitation Wednesday night into Thursday. This will
be followed closely by another strong, although not as cold, cold
front on Friday. The mountains will pile up some good snow as
active weather continues through the end of the week, and some of
this may spill over onto the east side at times. After a brief
brush with winter early next week, the west side will see only
rain later in the week. -Wright
Aviation...03/06z taf cycle...coastal areas from Cape Blanco
northward will likely have light rain into the evening with IFR
ceilings as a front moves onshore. Expect localized lower vsbys in
showers, as well. MVFR ceilings, along with mountain obscurations,
will develop through the overnight hours across the forecast area.
IFR to LIFR cigs will develop late tonight on the west side...most
likely in the Umpqua valley...including krbg. All areas will
improve to VFR Saturday afternoon. Btl
Marine...updated 0230 am PST Saturday, 3 December 2016...
very long 19 second period swell is mixing with shorter period
swell and will become dominant around 16 feet at 17 seconds late
this morning. Expect waves to break further from shore than normal
today, with a larger than normal surf zone. A cold front will move
through Sunday with increasing wind speeds and a well defined wind
shift behind the front. Winds should be strongest north of Cape
Blanco Sunday morning. After unsettled, showery conditions early
in the week, a much stronger and wetter frontal system is expected
Wednesday through Friday with a period of gales likely. Btl/sk
or...beach hazards statement through this afternoon for orz021-022.
Pacific coastal waters...Small Craft Advisory for hazardous seas
until 4 PM PST Tuesday for pzz350-356-370-376.