Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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525
FXUS66 KSEW 281539
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
900 AM PDT TUE JUN 28 2016

.SYNOPSIS...High pressure aloft will bring fair weather to Western
Washington today through Thursday. Weak onshore flow will result
in some night and morning cloudiness, but the days should be
mostly sunny a little warmer than normal. An upper trough will
bring cooler, cloudier weather and a chance of showers this
holiday weekend.

&&

.SHORT TERM...A weak short wave aloft induced an onshore push
overnight with low clouds spreading into most of the interior
lowlands. Current visible imagery and obs show the cascades,
Olympics, higher foothills, and Whatcom county cloud free. Stratus
tops are only around 1800 ft from a recent BFI pirep, and onshore
gradients are weakening favoring a rapid break out today. Mostly
sunny skies should prevail across the area by midday as a weak upper
ridge traverses the area. Given the extent of low clouds, the
forecast was updated to lower temperatures by a couple degrees
today.

Models and both the NAM/GFS MOS guidance show a return of low clouds
later tonight and Wednesday morning. Time-heights and forecast
soundings suggest a similar stratus intrusion as this morning.
Clouds should again burn off rapidly by late morning with mostly
sunny skies across the interior in the afternoon. Temperatures
were knocked down a couple degrees and morning cloud cover was
increased in the recent forecast update. Highs will again top out in
the mid to upper 70s around greater Puget Sound.

A short wave passing north of the area on Thursday will suppress
heights and maintain light westerly onshore flow. 500 mb heights are
still near or above 5800m and models point to a limited marine
stratus intrusion that will likely only reach Shelton and areas
along the Strait. Clouds will persist along the coast but sunny
skies should prevail over the interior. Highs will again be in the
mid to upper 70s. Mercer

.LONG TERM...For the extended period Friday through Independence
Day the models disagree on details, but they do agree that an
upper trough will begin moving over the region Friday for a trend
toward somewhat cloudier and cooler weather. By Saturday there is
a chance of showers across the forecast area, which will continue
through Monday. McDonnal

&&

.AVIATION...Previous discussion...A upper level ridge will
remain centered over Idaho with southwest flow aloft over Washington
today and tonight. At the surface, onshore flow will continue. The
air mass is dry and stable except for marine stratus over western
areas. Stratus has moved inland early this morning and most land
areas have IFR or low end MVFR ceilings. The ceilings will lift later
this morning and the stratus should evaporate back to the coast in
the afternoon.  The stratus should return overnight, however it will
probably be less extensive than this morning.

KSEA...Southerly wind 4-8 kt his morning will become northerly in
the afternoon. Ceilings below 1k ft this morning should lift and
then scattered out around noon. More stratus is expected late
tonight. CHB/13

&&

.MARINE...Onshore flow will prevail through Friday with high
pressure offshore and lower pressure inland. At least small craft
advisory strength west winds will occur each day in the central and
eastern Strait with gale force westerlies also possible.

For tonight have issued a gale warning for the central and east
strait, along with advisories for the coast, Admiralty Inlet, and the
northern inland waters. 13


&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Gale warning central and east strait tonight.
     Small craft advisory coast, Admiralty Inlet, and northern
     inland waters.

&&

$$

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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