Scientific Forecaster Discussion

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Area forecast discussion...updated 
National Weather Service Medford or
454 am PDT Wednesday Apr 16 2014

Updated aviation section

Discussion...a lot of minor changes were made to the forecast
grids this morning, but nothing major. A roughly zonal 100 knots or
so upper jet remains aimed at the Pacific northwest coast this morning.
We had a fair amount of wave cloud streaming off the Cascades and
across the east side overnight, but it is diminishing and starting
to shift east. The west side is in a break in the clouds, but
marine stratus has edged onto the north coast and a rather
expansive and continuous area of middle and high cloud can be seen
approaching the coast. This will make for a mostly cloudy day west
of the Cascades, but there will be some holes through which the
sun will poke occasionally, especially the further south one gets.
I don't expect too much change in temperatures compared to
yesterday, so today's forecast is similar to yesterday. The vast
majority of our area will not see any rain today, but as the
marine layer thickens later today and tonight, we may see some
drizzle along the north coast.

A frontal system currently out near 150w is moving rapidly our way
and will arrive Thursday. This is not a particularly strong or
wet system, but it should be capable of producing precipitation
nearly anywhere Thursday into Thursday night. The trajectory of
the system will certainly target the north coast, Umpqua basin,
and Cascades for the most precipitation, but all of US stand a
reasonable chance for some rainfall. Snow levels will be pretty
high with this system so snowfall is not going to be a big deal,
but we could see some light accumulations around Crater Lake. The
models are also showing a brief period of instability over lake
and Modoc counties Thursday afternoon and evening, so a slight
chance for thunder was added there.

Showers may linger into Friday morning, but the system moves away
quickly enough that the balance of Friday should be dry area-
wide. The models continue to trend drier over the weekend than
they had been. The reason seems to be a tendency to dig more
energy further west which slows the next front and forces it
further north. Didn't make any changes to the going forecast over
the weekend, so it still shows the best chance for any rain to be
along the coast on Saturday. The rest of the area looks to be dry
and probably with above normal temperatures as heights rise over
the intermountain west. There is reasonable model consistency in
showing the aforementioned energy coming into the pacnw in some
form early next week. However, the models differ in the details
quite a bit. For this reason, kept probability of precipitation and temperatures near
normal levels next week. -Wright


Aviation...based on 16/12z taf cycle...expect mostly VFR again
today, but there can be areas of MVFR ceilings with local terrain
obscured from the Cascades west to the the Umpqua valley and the
coast this morning. Any lower ceilings should improve to VFR by middle-
late morning. Expect MVFR ceilings and patchy drizzle to return to
the coast tonight while inland areas remain VFR. Spilde


Marine...gusty north winds and steep seas will persist in a small
area south of Gold Beach today...between about 5 and 20 nm from
shore. As a result, conditions will remain hazardous to small craft.
The thermal trough along the coast that has been causing the north
winds and steep seas will weaken tonight into Thursday allowing
conditions to improve. A cold front will move through the waters
Thursday with a period of rain. Light to moderate south winds will
shift to north in the evening. High pressure will briefly build
Friday...then another front will move through Saturday. Long period
westerly swell...about 12-14 feet at 14 seconds...will develop
Saturday night into Sunday. Spilde


Mfr watches/warnings/advisories...


Pacific coastal waters...Small Craft Advisory for winds until 8 PM PDT
this evening for pzz356-376.
Small Craft Advisory for hazardous seas until 8 PM PDT this
evening for pzz356-376.