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Area forecast discussion 
National Weather Service Seattle Washington
416 am PDT Sat Oct 1 2016

Synopsis...an upper level low will remain offshore today. The low
will move southeast into southwest Oregon by Sunday afternoon with
the showers chances decreasing over the area. A weak ridge of high
pressure will move over the area on Monday. A splitting weather
system will arrive on Tuesday.

&&

Short term...satellite imagery shows upper level low offshore
centered near 49n/133w at 10z. Showers rotating around the low
already moving into western Washington early this morning. Under
mostly cloudy skies temperatures were in the mid 40s to mid 50s at
3 am/10z.

Upper level low will continue to move south southeast today with
the low center about 250 nm west of Hoquiam by 00z Sunday.
Diffluence aloft over western Washington all day. Lifted indexes
lowest along the coast during the day ( 0 to -2 ) and over the
southwest interior in the afternoon (-1 to -2 ). Coldest air aloft
remaining offshore near the low. 500 mb temperatures along the
coast -25c with slightly warmer values over the interior. Will
keep the thunderstorm chances confined to the coast all day and
over the southwest interior in the afternoon. Showers spinning out
of the low moving across western Washington so have likely or
categorical pops for the entire area. High temperatures will be
below normal...in the upper 50s to mid 60s.

Low drifting a little south tonight with southerly flow aloft
over western Washington. Showers will remain in the forecast for
the entire area with lower pops to the north and the higher pops
over the southern portion of the area. Lows will be in the mid 40s
to lower 50s.

Low dropping south southeast Sunday morning with the low moving
inland over southwest Oregon Sunday afternoon. Low still close
enough on Sunday for a chance of showers over the southern portion
of the area while the conditions dry out over the northern
portion. Clearing skies over the northern sections Sunday
afternoon. Even with the sunshine with the cool air mass over the
area highs will still be below normal...in the upper 50s to mid
60s.

A few lingering showers over the Olympics and south of Seattle
over the interior Sunday evening but with the low continuing to
move off to the southeast shower chances will be gone by midnight.
With some clearing lows will be cool...in the 40s for most
locations.

Dry day on Monday with a weak upper level ridge building into the
area. Low level flow turning offshore as the next frontal system
approaches the area. By afternoon the front will be close enough
to spread some mid and high level cloud cover into western
Washington but with the front weakening will stay with the mostly
sunny wording for Monday. Highs in the upper 50s to mid 60s will
be common.

Long term...very little confidence in the extended forecast this
morning. Models are very inconsistent. The GFS brings the
splitting front into western Washington on Tuesday. The European model (ecmwf) is
much slower with the front moving what is left of the system into
the area late Tuesday night and Wednesday morning. More
inconsistencies later in the period with the GFS developing an
atmospheric river scenario later Thursday into Friday while the
European model (ecmwf) just has a cool upper level trough over western Washington.
Current forecast is more in line with the GFS solution early in
the extended and with the European model (ecmwf) solution later in the extended.
With no confidence in the model solutions at this point will leave
the current forecast that has some showers on Tuesday...chance of
showers Tuesday night into Wednesday and more chance pops Thursday
and Friday in for the forecast for this package. Felton

&&

Aviation...an upper low offshore will produce southerly flow
aloft for western Washington today and tonight. At the surface, a
low will shift north through the coastal waters today. The
remnants of this low will shift south into the Oregon waters
tonight. The air mass is moist and unstable.

Ksea...mostly VFR low clouds are likely today and tonight with
showers. Southerly wind 3-6 knots will increase to 10-15 knots
today and become gusty. There is a small chance of a thunderstorm
at the terminal today, mainly in the afternoon. Schneider

&&

Marine...a surface low will move north through the coastal waters
today. The low will bring Small Craft Advisory southeast winds
to parts of the waters today. The low will shift southeast into
Oregon tonight and Sunday.

A front will reach the area Monday night or Tuesday. Models are
having a hard time pinning down the details. There will also
probably be some 10-13 foot west swell behind the front Tuesday
night and Wednesday. Schneider

&&

Climate...Seattle ended the water year ( Oct 1 - sept 30 ) with
49.17 inches. This is the 6th highest total since records started
at sea-tac in 1945. The vast majority of the precipitation ( 88
percent ) fell in the first six months with the October 1 - March
30 total a record breaking 43.33 inches ( 154 percent of normal
value of 28.19 ). The second half of the water year ( April 1 -
sept 30 ) was very dry with only 5.84 inches ( 63 percent of the
normal value of 9.30 inches ). This was the 5th driest April
through September on record at the Airport. Felton

&&

Sew watches/warnings/advisories...
Washington...none.
Pz...Small Craft Advisory until 6 PM PDT this evening for 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.

Small Craft Advisory until 5 PM PDT this afternoon for Admiralty
Inlet-East Entrance U.S. Waters Strait of Juan de Fuca-
northern inland waters including the San Juan Islands.

&&

$$

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