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Area forecast discussion 
National Weather Service Seattle Washington
315 PM PST sun Jan 25 2015

Synopsis...an upper ridge over the region with surface high pressure
east of the Cascades will give dry and mild weather to the area
through Monday. A weak front will dissipate over western Washington
Tuesday through early Wednesday. Another upper level ridge will
build over the region later in the week.

&&

Short term...an upper level ridge is centered over Washington state
while a surface ridge extends from southeastern Idaho into eastern
Washington. Subsidence and drying in the lower levels has given a
very nice day to the area today with some record breaking maximum
temperatures.

Cirrus is topping the upper ridge this afternoon. This will likely
move off to the east of the area overnight allowing for good
radiational cooling. Dewpoint temperatures are still rather
high...near 50...and the inversion that is near 2000 feet this
afternoon is forecast to lower to around 1000 feet late tonight.
This means that areas of fog will redevelop over the interior
valleys and through the Chehalis gap. With less cloud cover this
evening...expect temperatures to drop 4-8 degrees cooler than they
did this morning.

Fog will lift midday on Monday...except maybe later in the afternoon
in the south interior where the valleys are blocked from the light
offshore flow. Afternoon sunshine and a continued warm air mass
means another very nice and mild day on Monday with highs again in
the 50s to around 60 degrees. The record high temperature at SeaTac
Airport on Monday is again 58 degrees and should be broken by a
degree or two.

The ridge shifts eastward into western Montana Monday night
as a frontal system and short wave trough offshore approaches the
area. However...the upper ridge appears to be strong enough to cause
the incoming front and upper level shortwave trough to mainly ride
by to the north of the area with little in the way of precipitation
in the interior of western Washington as the moves in and dies Monday
night through early Wednesday. Probability of precipitation were cut back a bit from the previous
forecasts for the Monday night through Wednesday time frame. Skies will be
cloudy and temperatures will be mild with lows in the 40s and highs
in the lower 50s Tuesday and Wednesday. Albrecht

Long term...a very weak short wave trough will move onshore Wednesday
night or Thursday. The 18z GFS is now dry with the Wednesday night and Thursday
system while the European model (ecmwf) brings some very light precipitation to the
coast. Will limit rain chances on Thursday to the coast. Model
consistency and continuity starts to suffer somewhat starting Sat
night with the faster 12z and 18z GFS bringing a front into the area
Sat night and sun and the European model (ecmwf) is about 18 hours slower...but still
faster than previous solutions. Will introduce clouds and a chance
of rain into the forecast starting Sat night and continuing into
Monday. With mean upper ridging along the West Coast...it will remain a
few degrees warmer than normal through early next week. Albrecht

&&

Hydrology...flooding is not expected for the next 7 days.

&&

Aviation...western Washington is at the northern periphery of strong upper
level high pressure right now. The ridge will move east tonight and
Monday...and an upper disturbance will move NE to the northern b.C. Coast
on Monday afternoon. Moderate to strong west-SW flow aloft. The air mass will
remain very stable. Through the air mass above is dry...the air mass
in the lowest 1000 feet is quite moist...with dewpoints in the 45-55
degree range. With this kind of moisture and only thin clouds
above...fog and very low clouds will be common tonight. On Monday
morning...the development of a gentle south breeze will help to
mechanically lift and disperse the fog by mid-day...with the most
stubborn spots for fog being over the south sound region around
shn/olm/tcm.

Ksea...VFR conditions expected through this evening...with only some
middle-high level clouds expected. Late tonight...high dewpoints and
light east wind will be favorable for fog development...most likely
on the dense side. On Monday...the development of a gentle south
breeze will first help to lift the fog into a low stratus late in
the morning...with burnoff expected around mid-day. Haner

&&

Marine...weak offshore gradients will persist through tonight. On
Monday afternoon...a 999 mb low will move NE to haida gwaii...bringing a
fresh south breeze to the coastal waters and a few locations over
the inland waters. The tail end of a trailing front will then pass
across western Washington on Monday evening...bringing a turn to westerly onshore flow
through Tuesday. A return of light offshore flow is forecast on Wednesday.

A marginal round of small craft advisories is in effect for
hazardous seas and rough bar. These conditions should settle down
tonight. Haner

&&

Sew watches/warnings/advisories...
Washington...none.
Pz...Small Craft Advisory for hazardous seas coast and West
Entrance until late tonight.
Small Craft Advisory for rough Grays Harbor bar this evening.

&&

$$

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