Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Medford or
313 PM PDT Wednesday Apr 23 2014

Short term...tonight through Sunday night.

The weather pattern will remain active through the weekend. But,
the most significant weather will occur during the next 48 hours.
A warm front is in place along the coast with light to moderate
rain extending into Douglas, western portions of Josephine and
Siskiyou counties...and also into western Klamath, and western and
northern portions of Jackson County. Rainfall is heaviest in the
coastal range as Red Mound has already received over six tenths of
an inch in the last 6 hours and more than three tenths of an inch
at Quail prairie. Rain will spread further inland during the
remainder of this afternoon and this evening with the majority of
precipitation occurring west of the Cascades with a snow level
around 6000 to 6500 feet.

The trailing cold front will arrive at the coast late tonight/early
Thursday morning with a period of enhanced rainfall rates through
the morning. This front will also create gusty breezy to windy
conditions with southerly winds that will be strongest at the
coast, in the Shasta Valley, and across the east side with gusts
up to 40 miles per hour. Winds will be strongest in the vicinity of the cold
front...at the coast late tonight and on the east side Thursday
afternoon.

The cold upper level low will approach the coast Thursday night
with embedded shortwaves in a west to southwest flow producing
scattered to numerous light showers and snow showers across the
area as the snow level falls from around 5500 feet to around 3000
to 3500 feet mean sea level. Thus, a light accumulation of snow on the major
Highway passes that are above 3500 feet is expected late Thursday
night into Friday morning. I blended the model solutions but
leaned a bit toward the wetter 12z GFS with a forecast of up to a
few inches of snow over the higher terrain.

The upper trough will move inland on Friday with a surface trough.
This boundary will bring scattered showers and a slight chance of
thunderstorms as it moves east across the area. The snow level
will reach its Low Point on Friday morning then it is expected to gradually
rise to around 4000 feet on the west side and 5000 feet on the
east side. Showers and snow showers will diminish Friday night as
the northern fringe of a ridge briefly nudges northeast into the
region.

The probability of precipitation has been lowered for Saturday
with most likely only some very light coastal and Umpqua valley
showers in a moist low-level onshore flow ahead of a cold front.
The models have not been consistent from day-to-day with the
strength of this front but have begun to show consistency in
timing it into the Pacific northwest and far northern California
Saturday night into Sunday. The 12z GFS and European model (ecmwf) both trended a
bit weaker with this front but I would not call it weak. Rain is
expected across most of the west side Saturday night with a snow
level around 4500 to 5000 feet before transitioning to lighter
showers on Sunday. Showers will diminish by Sunday night with a
high pressure ridge beginning to build into the area. /Dw

Long term...Monday through Wednesday night.

The ec...GFS...and dgex models all show a broad ridge along the West
Coast Monday morning. The ec solution shows 500 mb heights about
60-90m lower than than the GFS/dgex...but otherwise they are pretty
much the same.

Given the relatively flat nature of the ridge...expect plenty of
high clouds over the area but no precipitation. Medium-range
guidance reflects the height disparity between the ec and GFS/dgex
with the former depicting slightly below normal inland temperatures
and the latter slightly above normal.

The ridge will move slowly east Monday into Wednesday...but it will
amplify as it does so in response to a deepening long wave trough
between 130w and 150w. 500 mb heights over the area will rise quite
a bit Monday into Tuesday...so expect continued dry weather with a
warming trend.

The uncertainty factor in the forecast increases quite a bit
Wednesday as the model solutions diverge on the fate of the offshore
trough. The GFS/dgex brings the long wave trough to 130w Wednesday
morning...and this scenario would support a land falling front
Wednesday. Meanwhile the ec keeps the trough out between 140w and
150w...which would support another warm and dry day over the
forecast area. Will introduce some probability of precipitation to the forecast for
Wednesday but will not go whole hog yet. /Jrs



&&

Aviation...based on 23/18z taf cycle...VFR conditions will prevail
initially except for areas of MVFR ceilings and local IFR ceilings/visibilities
along the coast. The lower conditions will spread inland to the
Cascades through this evening with higher terrain becoming
obscured. The lower conditions will prevail into Thursday afternoon
before improving. East of the Cascades...VFR conditions will
prevail with gusty winds...but some of the higher peaks will become
obscured this afternoon into tonight. /Jrs



&&

Marine...upated at 255 PM PDT. South winds will increase to gale
force late this afternoon and continue over night. This will also
lead to very choppy wind generated seas...mostly north of Cape
Blanco. Winds will turn more westerly and decrease late tonight
dropping below small craft level by late Thursday morning. Another
front will bring strong winds and steep seas to the region this
weekend as well. /Mnd



&&

Mfr watches/warnings/advisories...
or...none.

California...none.

Pacific coastal waters...Small Craft Advisory for winds until 11 am PDT
Thursday for pzz350-356-370-376.
Hazardous seas warning until 11 am PDT Thursday for
pzz350-356-370-376.
Gale Warning until 11 am PDT Thursday for pzz350-356-370-376.
Small Craft Advisory for hazardous seas until 11 am PDT Thursday
for pzz356.

$$

Dw/jrs/mnd