Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 291018
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
320 AM PDT Sat Apr 29 2017

.SYNOPSIS...An exiting upper level ridge will keep this morning dry
but a weak front will spread inland starting late this morning to
bring light rain to the area once more. Showers will linger Sunday
and possibly into Monday. Upper level ridging returns late Monday
and stretches out into Thursday bringing drier conditions and warmer
temperatures.

&&

.SHORT TERM...Current radar and satellite are pretty quiet this
early morning. While skies are not completely clear...they have
cleared enough to provide a cool start to this morning with many
locations reporting temps in the upper 30s to lower 40s...although
portions of Whatcom and Skagit counties...retaining a bit of cloud
cover...are proving warmer with temps in the mid to upper 40s.

Upper level ridging will cross the state today as a frontal system
rides hot on its heels. Far northwestern portion of the CWA may
start to see precip just before noon today...but most locations
likely will not see precip until mid or late afternoon and
continuing into late tonight. The front looks to get hung up over
the Cascades by Sunday morning...deteriorating as time
progresses...but that looks to be enough to keep some precip in the
forecast for most of the day Sunday...although pops will not be
terribly impressive...mostly in the chance range. Models agree on
both an upper level ridge building in over the area Monday as well
as some form of showers being in place but with high pressure both
at the surface and at the upper levels...well...find it difficult to
see where such precip would come from. Still...kept low end chance
pops in the forecast but if models remain consistent in these
features...would not be afraid to bet on dry conditions.

Temperatures in the near term generally remaining steady although
sadly remaining below normal with interior locations generally
seeing afternoon highs in the mid to upper 50s while coastal
locations will remain in the lower to mid 50s.  SMR

.LONG TERM...It has been a rare thing this spring to be able to
chain together more than one dry day...but the ridge for late Monday
through early Thursday morning just might be a chance for doing so.
Before completely grasping onto that optimistic
solution...however...it must be pointed out that a system does pass
just to the north of the CWA in this time span on Wed morning. The
GFS has it just nicking the very northernmost portions of the CWA
while the ECMWF remains true to form and offers a wetter solution.
While it may end up being a gambler`s fallacy...currently siding
with GFS solution for no better argument than W WA`s luck has to
change sometime. Plus...cannot turn away from the prospect of
afternoon high temperatures getting close to 70 on Wed. Late
Thursday morning shows an upper level ridge passing through B.C.
which may allow for precip for the northern half of the CWA into
Thursday evening before ridging over the Pacific allows for
conditions over W WA to dry once more for Friday. The
ECMWF...however...shows a fairly deep trough over the western US at
this time...so...as has been the case for at least the past couple
of weeks...long term models remain generally uncertain and as such
lowering any degree of confidence in the extended forecast.  SMR

&&

.AVIATION...High pressure will shift east this morning, then trough
approaching the region this afternoon will move through the area
this evening. Light to moderate southwesterly flow aloft becoming
westerly this evening behind the surface front. The air mass is
mostly dry and stable today. Lower VFR stratus and light rain will
at the coast this afternoon...spreading inland by late afternoon or
early evening. A transition to showers should occur by midnight,
then decrease overnight.

KSEA...southerly wind 4 to 6 kt rising to 10 to 12 knots after
18z...then breezy southwest winds 13-16 kt w/ gusts to 25 knots
along and behind the front this evening. The front is expected to
pass the terminal around 06z this evening.

&&

.MARINE...Generally light flow this morning ahead of an approaching
front. Small craft winds will develop over the coastal waters later
this morning and strengthen up to 30 kt this afternoon. A switch to
westerly is expected by late afternoon, gradually easing through
midnight. A westerly push of small craft winds are likely to develop
behind the front in the central/eastern Strait later this evening
through early Sunday morning. Winds over waters adjacent to the
eastern strait could reach near-small craft strength during this
period.

Onshore flow will weaken Sunday into early next week with a lull in
wind across the area through at least Tuesday and possibly
Wednesday. The next front may reach the waters by Thursday but
timing is highly uncertain. dtm


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory coastal waters from 8 AM PDT through 11 PM
     this evening.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html



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