Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 272223
Area Forecast Discussion
National Weather Service Seattle WA
330 PM PDT WED JUL 27 2016
.SYNOPSIS...Upper level ridging and weak low level onshore flow
will remain in place over Western Washington through Friday. This
pattern will produce sunny days with temperatures well above normal.
Lower temperatures are likely over the weekend as an upper level
trough moves by to the north. A stronger upper level trough could
arrive around Tuesday.
.SHORT TERM...Satellite imagery shows stratus has evaporated back to
the coast. Highs today will top out in the mid 70s to mid 80s
inland, perhaps just touching 70 on the coast. Onshore gradients are
somewhat weaker than yesterday afternoon. Stratus penetration
overnight will likely be slightly less than last night. The Puget
Sound area should remain largely clear with stratus not making it
much farther inland than Shelton in the southwest. Stratus will also
probably reach most of the way down the strait.
Thursday will have temperatures well above normal with a flat upper
level ridge over the area and light surface gradients. 500 mb
heights and 850 mb temperatures will peak on Thursday with 500 mb
heights approaching 590 dms and model 850 mb temperatures in the
plus 16-19c range. Thursday looks to be the warmest day in the short
term with highs in the interior in 80s to near 90 and highs on the
coast in the mid 70s.
Friday will be a transition day across the area with the low level
flow turning onshore during the day. Heights will fall a bit. The
coast will cool Friday with the increasing onshore flow resulting in
5 degrees or so of cooling. For the interior model guidance has
backed off from any major cooling and now is only a few degrees
lower than Thursday. Saturday will feel the effects of an upper
level trough moving through southern British Columbia as heights
fall into the 570s. There will probably also be a decent marine push
Friday night. Clouds will increase and high temperatures will be
lower on Saturday. Burke
.LONG TERM...Sunday remains troffy and there could be a few light
showers. Monday looks dry and warmer. An upper level low moves
through the region around Monday night and Tuesday with some
recovery in heights Wednesday. Temperatures will be near normal each
day and there is a slight chance of showers, mainly in the
.AVIATION...A flat ridge of high pressure will give light
westerly flow aloft. At the surface, high pressure over the
offshore waters and lower pressure east of the Cascades will give
northwesterly flow at lower levels. The air mass is dry and stable
with low level moisture mainly over the coastal waters.
Visible satellite imagery shows low stratus now confined to the
coastal waters and the immediate coastline. Elsewhere, good VFR
conditions dominate and will continue through tonight. Stratus
will continue along the coast through Thursday. Patchy low
stratus and some fog will form into the interior Thursday morning,
mainly through the Chehalis Gap and over the interior waters. Any
stratus and fog that forms in the interior will begin around 12Z
and will dissipate by 18Z. Albrecht
KSEA...Clear skies through tonight. Shallow stratus and fog that
reforms to the south of the terminal Thursday morning and another
batch around KPAE should not impact operations at the terminal.
Winds northwest 5-9 kt this afternoon will shift to 02005kt after
04Z then diminish after 08Z. Albrecht
.MARINE...A ridge of high pressure over the offshore waters will
give moderate to strong northwesterly flow from off the central
portion of Vancouver Island southeastward through the outer
portion of the Washington coastal waters through Thursday night.
The northwesterly winds will increase to near-gale to gale Friday
through Saturday resulting in a steep wind wave or fresh swell. A
small craft advisory is in effect for the outer portions of the
coastal waters through Thursday night.
Higher pressure offshore combined with lower pressure inland
is giving low level onshore flow to the inland waters. Expect
small craft advisory conditions to develop late this afternoon
and tonight through the central and eastern portions of the Strait
of Juan de Fuca. Late Thursday afternoon through Thursday night
should be a repeat. Onshore flow will increase late Friday and
will continue through Saturday as an upper level trough of low
pressure moves across the region, tightening surface pressure
gradients. While winds will increase, models show the disturbance
late in the week being weaker than earlier anticipated. At this
time the forecast will indicate 20 to 30 knots of westerly inflow
for the central and east portions of the strait late Friday
afternoon and Friday night and again on Saturday. Albrecht
PZ...Small Craft Advisory until 3 AM PDT Thursday for Central U.S.
Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
Strait Of Juan De Fuca.
Small Craft Advisory until 4 PM PDT Friday 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.
You can see an illustrated version of this discussion at