Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 270952

Area Forecast Discussion
National Weather Service Seattle WA
252 AM PDT Thu Oct 27 2016

.SYNOPSIS...Locally heavy rain that was associated with a slow
moving cold front overnight has moved into the Cascades. An upper
level will keep showers in the forecast through this evening.
Weak high pressure will build east of the Cascades on Friday
giving some drying to the interior. Then a series of weather
systems will give unsettled conditions to the area from the
weekend through much of next week with only brief dry periods
between systems.


.SHORT TERM...The slow moving cold front that brought impressive
rainfall rates to the central portions of the Puget Sound area
last evening has finally moved off into the Cascades. Radar shows
only very light rainfall remaining across the interior at this
time. The Urban and Small Stream Flood Advisory that was issued
for the central portions of the Puget Sound area late last evening
was allowed to expire as a result.

A sharp upper level trough remains just outside of 130W early
this morning, and area radars show bands of showers in the post-
frontal environment. At 2 AM one was located from the Olympics to
just north of Hoquiam. Another band was seen moving onto the
north coast. A more consolidated band of showers extending
southwest from the central portions of Vancouver Island is
associated with the bent-back occlusion from the mature low moving
onto northern Vancouver Island early this morning. Short term
models show these shower bands moving slowly east through this
evening as the offshore upper trough lifts to the northeast, so
while there may be some dry periods today, showers will likely
affect most locations.

Weak high pressure will build over Eastern Washington on Friday as
another weak frontal system brushes the Olympic Peninsula. Clouds
and a chance of showers can be expected from the Olympics westward
across the coastline with the front, but light offshore pressure
gradients should result in temporary drying and some clearing in
the interior by Friday afternoon.

All models show moisture surging northward into the area on
Saturday as a weak system associated with an upper level trough
moves north through the coastal waters. Rain will be likely along
the coast and on the Olympic Peninsula while the interior will see
a good chance of rain.

Temperatures will range from the mid 40s to around 50 at night and
in the mid 50s to lower 60s during the day today through
Saturday. These temperatures are about 2-4 degrees above normal
for this time of year. Albrecht

.LONG TERM...Global models all show a split flow pattern
dominating along the west coast of the US from Sunday through the
middle of next week. A weather system on Sunday will pass mainly
to the south of the area with Western Washington seeing clouds and
best rain chances south of Seattle. A weak northern stream system
moving through mainly British Columbia will give a chance of rain
on Monday and possibly into early Tuesday. A ridge of high
pressure aloft and low level offshore flow gives the best chances
for dry weather later Tuesday into possibly early Wednesday. The
weather will likely become increasingly active late next week as
the upper level flow consolidates along about 45N. The only change
to the forecast was to decrease pops a bit on Tuesday with the
passing upper ridge. Otherwise the previous long term forecast
looks good. Albrecht


.AVIATION...Southwest flow aloft will continue today and tonight
over Washington. There will be scattered showers or rain bands today
in the wake of a front that passed last night. The air mass is moist
and weakly unstable.

Conditions are generally VFR with ceilings 5k ft or so. MVFR
conditions are briefly possible in showers. VFR conditions are likely
to continue today and tonight.

KSEA...Discussion above applies. Southerly wind 8-12 KT. CHB


.MARINE...Gradients will ease today as a low center dissipates over
northern Vancouver Island. Small craft advisory strength winds will
continue this morning, then diminish after noon. A weaker low will
approach the coast tonight and dissipate over the offshore waters
Friday. Another low will move into northern California Sunday. CHB


.HYDROLOGY...After seeing 18-hour rainfall amounts in the central
Puget Sound area of about 1 to 1.3 inches, another half inch of
rain fell in just 1-2 hours late last evening. This produced some
urban and small stream flooding in the greater Seattle area late
last evening. The rain has decreased in intensity and moved off
into the Cascades, so the Urban and Small Stream Flood Advisory
that was issued shortly after 11 PM last evening was allowed to
expire. Rivers flowing off the Olympics and Cascades saw rises
from Wednesday`s rainfall, but all will crest well below flood

Hydrologically significant rainfall is not expected for the next
several days, so area rivers are not expected to flood for the
7 days. Albrecht


PZ...Small Craft Advisory until 11 AM PDT this morning for Admiralty
     Inlet-Coastal Waters From Cape Flattery To James Island 10
     To 60 Nm-Coastal Waters From Cape Flattery To James Island
     Out 10 Nm-Coastal Waters From James Island To Point
     Grenville 10 To 60 Nm-Coastal Waters From James Island To
     Point Grenville Out 10 Nm-Coastal Waters From Point
     Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters
     From Point Grenville To Cape Shoalwater Out 10 Nm-East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands-Puget Sound and Hood
     Canal-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory for rough bar until 6 AM PDT early this
     morning for Grays Harbor Bar.



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