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Area forecast discussion 
National Weather Service Medford or
848 am PDT Wednesday Jul 23 2014

Discussion...already made a quick update this morning to raise
probability of precipitation associated with a frontal band moving through the area right
now and am planning to update the rest of today shortly. There is
a potent upper low off the Washington coast right now, and an
associated cold front stretches southward from the low along the
pacnw coast. The main rain band currently stretches from around
Roseburg south through Josephine County and is moving east at
around 20 miles per hour which puts it at Medford around 930 am. While the
models show this front falling apart prior to reaching Medford,
radar doesn't suggest that, so we should see some rain this
morning. After the front moves through, it will become showery.
Most of the instability is well north of US, but we could see a
lightning strike here or there across the northern parts of our
forecast area. At any rate, it will be quite cool and damp for
this time of year today.

I do think the front (or at least its precipitation) will fall
apart as it is crosses over to the east side, but it will still
produce gusty west winds today east of the Cascades. Precipitation
will be much spottier over there, but showers will be possible
especially north. -Wright


Aviation...based on the 23/12z tafs...areas of MVFR and local IFR
ceilings and visibilities at the coast with light to moderate rain
will persist at the coast until around 18z as a cold front moves
across. Rain and isolated thunderstorms will spread inland this
morning with VFR ceilings transitioning to areas of MVFR
ceilings...mainly west of the Cascade crest. As the cold front
tracks inland showers and isolated thunderstorms will linger across
the west side into the early afternoon. The area east of the
Cascades will remain mainly dry today. But, this front will also
produce moderate to strong westerly low level winds with the
strongest 35 knots east of the Cascades during the
afternoon and early evening. Ceilings will rise and then
dissipate with VFR conditions this evening, except for coastal low
clouds that are expected to form around 06z and continue into
Thursday morning. /Dw


Previous discussion... /issued 329 am PDT Wednesday Jul 23 2014/

Short term...a low pressure system will bring a front inland
today while a shortwave moves up from the south ahead of the front
and moves across the County Warning Area this morning into early this afternoon. This
pattern will bring rain showers today with isolated thunderstorms
expected. Cooler temperatures are also expected today.
Additionally, strong gusty winds will occur with this front from
the Cascades eastward. The upper low will shift inland
tonight...then northeast on Thursday. So expect continued cooler
than normal temperatures for inland areas on Thursday. Along the
coast, a thermal trough develops on Thursday and strengthens Friday
while an upper ridge builds overhead Friday. This will bring gusty
north winds to the coast and much warmer temperatures across the
area Friday. the front moves inland expect rain showers to spread
into the area. Additionally isolated thunderstorms are possible
across much of the area this morning into early this
afternoon...then isolated thunderstorms possible from the Cascades
east late in the afternoon. Instability is forecast ahead of and
with the frontal passage and the front combined with a shortwave
moving up from the south are expected to help trigger
thunderstorms. Also an upper level jet will push inland today
providing upper level support for convective activity. Lifted
indices and cape are relatively weak though so expect mainly
isolated storms. A favored area for thunderstorm
development is expected to be from the western foothills of the
Cascades in Oregon extending east of the Cascade crest.

Also with this front, southwest to west gusty winds are expected
east of the Cascades today. Models and guidance are in good
agreement showing gusts of 30 to 40 miles per hour possible.

Behind the front, expect cool conditions overnight with
temperatures lowering into the middle 30s to low 40s east of the
Cascades and in the lower 50s for west side valleys. During the
day Thursday, temperatures will remain below normal for inland
areas but skies will become mostly sunny across the area. A mild
Chetco effect may be felt at Brookings as north to northeast winds
develop due to a thermal trough building along the coast.

By Friday, expect a return to normal conditions with warm
temperatures and dry conditions as an upper level ridge begins to
build over the region and a thermal strengthens along the coast.

Long term...then hot conditions are expected across the area this
weekend as an upper ridge strengthens over the region. Also a
thermal trough will bring gusty north winds along the coast.
Models are indicating that an upper low will drop down into the
Gulf of Alaska over the weekend and some weak shortwave activity
may move into the County Warning Area with southwest flow aloft on Sunday. Have
kept the forecast dry for now. However, if future runs continue
to show shortwave activity, may need to add a slight chance for
thunderstorms into the forecast for Sunday. Then early next week,
models begin to show some monsoon moisture moving into the area by
Tuesday with a slight chance for thunderstorms expected over
inland areas, mainly from the Cascades west in Oregon and across
northern California.

Marine...updated 230 am PDT 23 July 2014...confidence is high in
the forecast for today with the passage of a wet cold front, and
also high in a change in the surface pressure pattern to follow. A
thermal trough will rapidly develop on Thursday then likely linger
through the weekend into early next week. This will likely result
in moderate to strong north winds and steep wind driven seas with
the strongest winds during the afternoon and evening hours in the
outer waters south of Cape Blanco. The main uncertainty in the
forecast relates to the strength of northerly winds from Thursday
through the end of the forecast period...specifically how far to
the north Small Craft Advisory level winds will extend and whether
winds in the outer waters south of Cape Blanco will reach gale
force. The 00z GFS model is stronger than the NAM with winds north
of Cape Blanco while maintaining its normal bias of not bringing
the strong northerlies close enough to the coast. A model blend
was utilized. Winds look to remain generally below Small Craft
Advisory levels within 5 nm of the coast while winds in the
southern outer waters are expected to be below gale force on
Thursday but then a bit stronger...likely reaching gale force
Friday afternoon and possibly during each afternoon and evening
into early next week. /Dw


Mfr watches/warnings/advisories...

Pacific coastal waters...none.


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