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Area forecast discussion 
National Weather Service Medford or
515 PM PDT Monday Mar 30 2015

Updated aviation and marine discussions.

Short term...afternoon infrared satellite imagery is showing a cold
front near 130 west advancing toward the coast. Warm conditions
precede the front over southwest Oregon and northern California
this afternoon. The warmth will be a fading memory Tuesday as a
much colder air mass moves in overhead. We can see evidence of the
cold air mass aloft with all the cold core cumulus clouds behind
the front over the Pacific Ocean. The front itself will move
through the area tonight into Tuesday morning with a band of
mostly light to moderate precipitation expected from the coast to
the Cascades. East of the Cascades, precipitation with the front
will diminish to isolated/scattered showers Tuesday, but it will be windy at
times. By far the most noticeable change will be the 15-25 degree
drop in high temperatures from today to Tuesday. More numerous
showers are expected along and west of the Cascades due to moist
westerly onshore flow and a short wave moving inland. Snow levels
will drop down to around the major passes (4500 ft) and a small
accumulation of snow is likely above 5000 feet. Isolated
thunderstorms may also develop along the coast north of Cape
Blanco and into portions of northwest Douglas County as the pool
of sub -30c air at 500 mb grazes the area. Graupel/small hail is
possible in the heavier showers.

Tuesday night into Wednesday morning...the main short wave will
move east of the area and showers will retreat back to areas
along the coast and mainly north and west of the Umpqua Divide.
Expect enough drying to allow clouds to break over northern
California. As a result..a freeze watch is in effect for portions
of the Shasta Valley. Cloud cover will probably break at times in
the Rogue Valley too...but temperatures should largely remain
above critical freeze thresholds.

Another shortwave disturbance will move southeastward down the
back side of the trough Wednesday reinforcing the chilly air mass
over the area. The air mass won't be as moist, so showers won't be
as numerous, but still expect some out there, especially during
the afternoon and evening. Again, the air mass will be quite
unstable, so any of the heavier showers that do develop will have
the capability of producing thunder along with graupel/small

Additional frost/freeze products for some of the valley locations
in northern California and in Oregon west of the Cascades may be
necessary Wednesday and Thursday night. High pressure will build
in, the air mass will dry out and the potential for cloud-cover
will lessen. Right now, the greatest threat for a freeze in the
Rogue Valley is Thursday night into Friday morning. Spilde

Long term...Friday through Monday...short wave ridging continues
into Friday for dry weather for most of our forecast area. The
exception is our northwest corner in Coos and Douglas County where the next
front approaches. Timing is similar on both the GFS and European model (ecmwf) with
the GFS showing slightly higher precipitation amount. Therefore
confidence is moderate to high that we will see some rain there
on Friday.

Elsewhere clearing skies may allow min temperatures to dip closer to
freezing for the rural area of Rogue Valley Friday morning. For next
weekend...both GFS and European model (ecmwf) are still consistent at dropping a
broad trough into the Easter Pacific and the West Coast. We're
continuing to steer with the cooler and showery forecast. Both
models maintain the previous track with the European model (ecmwf) placing the low
farther offshore and a more SW flow into our forecast area...whereas
the GFS places the trough right over the Pacific northwest. Confidence is
moderate to high that we will see precipitation next weekend but
confidence is not very high on amount to put more than chance probability of precipitation
at the moment. /Fb


Aviation...for the 31/00z taf cycle...a cold front will bring
stronger south winds to the coast this evening continuing into
tonight. Ceilings are expected to lower to MVFR this evening as the
front approaches with coverage becoming widespread overnight with
coastal mountains and terrain becoming obscured. MVFR ceilings will
spread into the Umpqua basin early Tuesday morning with the front.
As rain spread south into the Rogue Valley after midnight...expect
local MVFR ceilings in the Rogue Valley with mountains obscured. East of
the Cascades..gusty westerly winds are expected Tuesday afternoon.
Cloud bases will lower overnight but is expected to remain VFR east
of the Cascades.

Also of note...the cold front will bring freezing levels down by
5000 feet from this evening through Tuesday morning. Additionally...
isolated thunderstorms are possible Tuesday afternoon north of Cape
Blanco from the coastal waters east into to Roseburg. Sk


Marine...updated 3 PM PDT Monday 30 Mar 2015...south winds will
increase this afternoon and evening ahead of a cold front...which
will move onshore tonight. Seas will reach Small Craft Advisory
criteria over the whole area...but small craft winds will be limited
to areas north of Cape Arago and beyond 10nm offshore...except near
shore from Reedsport northward. The small craft seas will be
primarily due to a moderate west swell with the period around 14
seconds that will persist into Tuesday evening.

High pressure will briefly rebuild from the southwest Tuesday...but
it will remain cool and showery with isolated thunderstorms north of
Cape Blanco. A weak low pressure will move into the waters Tuesday
night...with continued unsettled weather. Offshore high pressure
will redevelop Wednesday night and persist through Friday morning.


Mfr watches/warnings/advisories...

California...freeze watch from late Tuesday night through Wednesday morning
for caz081-281.

Pacific coastal waters...Small Craft Advisory for hazardous seas from
5 PM this afternoon to 11 PM PDT Tuesday for
Small Craft Advisory for winds from 5 PM this afternoon to
11 PM PDT this evening for pzz350-370-376.



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