Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Medford or
849 PM PDT Sat Apr 19 2014

Discussion...a weak cold front moved through the area this
afternoon and is on its way into Nevada and Idaho this evening.
Precipitation with the front remained largely north and west of
the Rogue Valley with highest amounts of 0.10-0.20 of an inch
along the coast and also portions of the Umpqua valley.

Gusty winds over the area this afternoon are in the process of
easing this evening and will likely go calm in many areas
overnight as short wave ridging builds in. With clearing skies,
temperatures will drop into the middle 30s in some of typically
colder spots of Josephine and Jackson counties. Expecting a low
near 38 in Medford and Grants Pass, but some local spots may dip
down to 34 or 35 around sunrise. A frost advisory (npwmfr) remains
in effect. After a chilly start, Easter Sunday will have a mild
afternoon with highs in the upper 70s.

The next stronger front will arrive at the coast Monday
afternoon, then move inland Monday night. Expect another period
gusty winds ahead of this front, especially over the east side.
Most areas should get wet with the front Monday night into
Tuesday. Further details follow in the previous discussion
below. Spilde


Aviation...based on 20/00z taf cycle...clouds and wind will both
continue to decrease this evening as a front moves east of the
area. VFR conditions are expected for the remainder of the night
except along the coast and Umpqua (including koth and krbg) where
some radiational stratus and fog with IFR to LIFR ceilings/visible will be
possible around dawn. After the aforementioned stratus/fog Burns
off tomorrow, VFR conditions are expected area wide. -Wright


Marine...a very heavy west swell will arrive tonight and
continue into Sunday. The swell has finally arrived at buoy 46002
where it peaked at 23 feet 16 seconds a couple of hours ago. Swell
decay tools show that it will still be at around 20 feet with
periods lengthening to around 18 seconds when it arrives at the
coast overnight, so the hazardous seas warning was extended all
the way to the coast. The heavy swell will also support heavy
breakers over bars and within the surf zone. Fishing gear located
at depths of around 850 feet or less could be relocated or
damaged. Seas will subside Sunday afternoon and evening but will
remain at Small Craft Advisory levels through at least Wednesday
as several more swell trains propagate through the region.
Although numerous systems will pass over the area next
week...winds will remain relatively light. -Wright


Previous discussion... /issued 720 PM PDT Sat Apr 19 2014/

Short term...behind a weak front expect cool temperatures tonight
followed by a brief period of ridging and warm and dry conditions
Sunday. Then a more active and moist pattern is expected beginning
early next week.

Currently, a weak front has moved inland to the Cascades
and will dissipate over the area this evening. Periods of light
rain will continue mainly for the coastal areas and across Douglas
County. Behind this front expect clearing skies, although low
clouds will likely redevelop in the Coquille and Umpqua valley
late tonight. Cooler temperatures are expected tonight and Sunday
morning for west side valleys along with light winds. Have issued
a frost advisory for portions of Josephine and Jackson County due
to cold temperatures impacting agricultural interests.

On Sunday expect warm temperatures and dry conditions across the
area with an upper level ridge building inland and an upper trough
developing offshore. Low clouds and patchy fog in Coos and Douglas
counties is expected to clear in the late morning on Sunday.
Otherwise expect mostly clear to partly cloudy skies over the area
on Sunday.

Monday and Tuesday...models forecast a change in the weather
pattern. On Monday...models continue to indicate that a front will
move towards the area...then push inland Monday evening and
night. Ahead of the front, models indicate some southerly moisture
will move into the area and weak instability will develop along
the Cascades and into northern Klamath County. Currently have kept
mention of thunderstorms out of the forecast given the very weak
instability values but kept mention of a slight chance to chance
for showers across inland areas during the day Monday.
Inland...expect temperatures to remain relatively warm on Monday
with highs in the middle 60s to low 70s across inland areas. Breezy
and gusty south to southwest winds are expected to develop in the
afternoon and evening hours, especially across northern California
and from the Cascades east.

Then Monday evening and night, a cold front will move inland
bringing light to moderate precipitation across the area. Snow levels
will gradually lower with the frontal passage from around 6000 to
7000 feet Monday evening down to 5000 feet Monday night...with
snow levels expected to lower further to around 4000 feet Tuesday
morning as showers continue. On the backside of the front and in
showers expect some light snow accumulations over the higher

A cold showery air mass is forecast behind the front on Tuesday as
a large upper trough moves into place. Also the NAM and GFS show
increased instability with cold air aloft over areas east of the
Cascades Tuesday afternoon. So have expanded the slight chance of
thunderstorms to extend from the Cascades eastward on Tuesday.
Also, the NAM shows increased instability along the coast and into
Coos and Douglas counties Tuesday morning and have added a slight
chance for thunderstorms for these areas.

Models show increased variability concerning how much showers are
expected Tuesday night as the upper trough shifts east out of the
area. The operational GFS shows a stronger ridge developing offshore
and a brief period of drier weather possible Tuesday night while
the European model (ecmwf) indicates a weaker ridge with moist onshore flow and
additional showers over the area. Given the progressive pattern
with a strong upper level jet offshore, have leaned more towards
the European model (ecmwf) solution with showers likely west of the Cascades in
Oregon and slight chance to chance of showers elsewhere in the
County Warning Area. CMC

Long term...the operational ec and GFS remain in fairly good
agreement with the overall pattern through the period. Confidence is
moderate to high that we'll be cooler and unstable most of the time.
A high amplitude trough will move east of the forecast area
Wednesday with weak ridging building in and we could catch a
relative break in the weather, but confidence is not high. This is
because the ec shows warm front ahead of developing surface low that
could spread steady moderate precipitation to the northwest part of
the area. In contrast the GFS has the warm front positioned farther
offshore and there's more ridging. For now went with a blend between
the two. A cold front will move towards the area Thursday, but it
may be slow to move in because it's it's nearly parallel with the
upper flow. However the upper trough will dig south and a shortwave
will rotate around the base of the upper low, thus driving the front
into the area, but that may not happen until Friday. Next weekend is
likely to be cool and unsettled. Of note the rmop continues to show
a high probability (67%) of a deepening trough in the eastern
Pacific Friday evening, moving towards the Oregon coast Saturday
evening (56%), over our area next Sunday and Monday (49% and 43%),
these are considered pretty high values this far out and are higher
than what was shown yesterday. The good news is that the moisture
will be much needed and there is a chance we could add to the
snow pack over the higher elevations in the Cascades and Siskiyous.


Mfr watches/warnings/advisories...
or...high surf advisory until 11 am PDT Sunday for orz021-022.
Frost advisory from 2 am to 8 am PDT Sunday for orz024-026.


Pacific coastal waters...hazardous seas warning until 11 am PDT Sunday
for pzz350-356-370-376.
Small Craft Advisory for hazardous seas until 11 PM PDT this
evening for pzz350-356-370-376.
Small Craft Advisory for hazardous seas from 11 am Sunday to 5
PM PDT Tuesday for pzz350-356-370-376.