Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 252145
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
245 PM PDT MON JUL 25 2016

.SYNOPSIS...
A generally warm and dry weather pattern is set for the area
through the week. A weak and fast moving mid level system will
cross Western Washington and help to produce a slightly cooler
day Tuesday. After that exits to the east, a warming trend will
commence for mid-late week as mid level ridge of high pressure
builds in and sends temperatures above normal. A cooling trend is
expected for the weekend.

&&

.SHORT TERM...
A warm and quiet day in progress across the area. Satellite
indicates lingering low clouds hugging the coast tightly and most
of the mid and high level clouds have exited to the east.
Temperatures have responded well to the sunshine and at 2 pm,
readings are well into the 70s and 80s except some 60s on the
coast.

A subtle shortwave trough will push through the area later today
and into Tuesday. This will produce a decline of 500 mb heights
and 850 mb temps. Readings of +16C today will drop to around +12C
tomorrow. This plus the greater low level marine intrusion will
spell several degrees of cooling on highs for Tuesday. Typically
about 4-6 degrees inland, but little change along the immediate
coast. Following tomorrow`s brief suppression of mid level
ridging, there will be a warming trend by Wednesday. Heights will
rise with warming from the south and temperatures will climb back
to near today`s highs, with plenty of 70s and lower 80s.

.LONG TERM...
The mid level ridge over the desert Southwest will build north
and produce a marked increase in 500 mb heights by Thursday, with
heights up to about 588dm that morning. 850 mb temps around +17c
so will expect temps in the mid-upper 80s for Seattle area with
around 90 or low 90s across the south interior. Have begun to
highlight this warmth for Thursday as it should be the warmest
temperatures in over a month across the area. There remains some
disagreement on Friday as to how quickly the cooling begins with
the GFS being more aggressive in dropping heights on Friday.
Should this play out, it would be slightly cooler on Friday than
Thursday. However the ECMWF keeps the heights a little higher and
would be expected to mean Friday is very similar to Thursday. For
now will just go with that idea that Friday should be similar to
Thursday for highs. The discrepancy continues into Saturday. Both
models agree on a stronger mid level trough pushing into the west
coast of Canada but the GFS has a faster drop in heights and a
sharper cooling trend. ECMWF has cooling on Saturday but not as
dramatic. The official forecast blends the two solutions to show a
cooling trend but not as quick as the GFS. Solutions come into
better alignment on Sunday on heights and surface temperatures,
which bring readings below normal with trough over the Pac NW.

&&

.AVIATION...Expect light westerly winds aloft to persist through
Tuesday. Low level onshore flow will strengthen this evening as a
weak upper level disturbance moves across the region. The air mass
will be stable. Low level moisture over the coastal waters will
push inland and deepen overnight as the as the upper level
disturbance passes across the area.

Visible satellite imagery shows widespread stratus over the
coastal waters this afternoon. The stratus will push inland
overnight, reaching the interior terminals between 10Z and 12Z.
IFR ceilings between 700 and 1000 feet are expected at many
locations between 12Z and 19Z Tuesday. The stratus is expected to
lift and burn off in the interior by about 20Z Tuesday but
persist on the immediate coastline. Albrecht

KSEA...Expect scattered cirrus through much of tonight. Stratus
with bases 700-1000 feet will arrive at the terminal about 10Z
late tonight. NW winds 7-9 kt will veer to more north/northeast
this evening then will shift to south to southwest 5-7 kt by 10Z
as the marine stratus moves in. Albrecht

&&

.MARINE...High pressure offshore combined with lower pressure
east of the Cascades will give onshore flow for the upcoming
week. The onshore flow will become strong by 6 pm this evening as
an upper level disturbance moves through the area, tightening
pressure gradients. Westerly gales are expected to develop in the
central and eastern portions of the Strait of Juan de Fuca
early this evening, while small craft advisory conditions are
expected over southern portions of the Northern Inland Waters and
in Admiralty Inlet.

Moderate onshore flow will resume from Tuesday through Thursday.
Onshore pressure gradients will likely tighten again Friday
afternoon, although some long range models such as the ECMWF delay
the onset of the push by about a day -until Saturday. Small Craft
Advisory northwest winds are expected over portions of the
coastal waters for much of the upcoming week. Albrecht

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory until 2 AM PDT Tuesday for Coastal Waters
     From Point Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory until 9 AM PDT Tuesday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater 10
     To 60 Nm.

     Gale Warning from 6 PM this evening to 3 AM PDT Tuesday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 6 PM this evening to 3 AM PDT Tuesday
     for Admiralty Inlet-Northern Inland Waters Including The
     San Juan Islands.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html



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