Small Craft Advisory 76, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
300 AM PDT Sat Apr 1 2017

.SYNOPSIS...A weak cold front will bring a little light rain to
Western Washington this morning. Scattered showers will linger this
afternoon through Sunday as a weak upper level trough crosses the
area. Dry weather will return Monday and Tuesday as an upper level
ridge moves over the region. The weather will become wetter again
later next week as a series of fronts move onshore.

&&

.SHORT TERM...A weak front has moved onto the north coast early
this morning with some light rain extending from the coast into the
north interior. This will gradually spread inland this morning, but
amounts will be meager...a few hundredths at best for many spots.
The front pushes into the Cascades by late morning with decent post-
frontal onshore flow behind it. A convergence zone is likely to
develop this evening, but the remainder of the forecast area will be
mostly dry. A weak upper trough will move through early Sunday
morning. This will keep the convergence zone going into Sunday
afternoon or evening and enhance some mostly mountain shower
activity. Showers should dissipate Sunday night as onshore gradients
relax and flow aloft veers to the north-northwest. Monday looks dry
with heights gradually rising as a weak ridge moves into the
offshore waters. High temperatures through the short term forecast
period will be near or a little below normal.

.LONG TERM...An upper ridge axis will slide across the area
on Tuesday for a dry and seasonably mild day. The models have a warm
front brushing the north coast late in the day with a chance of rain
for coastal areas and the north interior. The Euro and GFS are in
pretty good agreement that the associated cold front will gradually
shift inland on Wednesday afternoon or night, but not before we
potentially get our warmest day so far this year (albeit over a
month behind schedule). If we have yet to reach 60 degrees in
Seattle by Tuesday or Wednesday, it would be the latest such
occurrence in more than 45 years. A upper level trough will park
offshore for the later half of next week with...you guessed
it...periods of light rain and temps running a bit below normal. 27

&&

.AVIATION...Westerly upper level flow will remain in place today and
Sunday in the wake of an exiting ridge. The expected front for this
morning making its way into NW portions of the CWA at the time of
this writing and will continue to spread over the area through the
morning hours...allowing for cigs to drop into MVFR...isolated
locations may dip down into IFR...as rain associated with this front
pushes through. Onshore flow will set up in the wake of the front.
Models remain consistent on a Puget Sound Convergence Zone setting
up late this afternoon and into tonight between SEA and PAE
potentially impacting those terminals as well as BFI. An upper level
trough will shift flow to the northwest Sunday and...with lingering
moisture in place...may still give rise to scattered showers.  SMR

KSEA...OVC conditions look to remain in place...currently at the mid-
levels but possibly dipping down into lower levels as front
approaches. FROPA still looks to be in the 12-15Z time
frame...although satellite trends may put its passage closer to the
tail end of that estimate. Light rain still expected to accompany
the front...although generally looking at cigs going no lower than
MVFR. PSCZ expected to develop late in the afternoon bringing
showers and continued MVFR cigs within the vicinity of the terminal.
SMR

&&

.MARINE...A cold front currently making its way through northern
coastal waters at the time of this writing is expected to pass over
remaining waters this morning and into the afternoon. Increasing
southerlies are expected in advance of the front transitioning to
onshore flow once the front passes. Models consistent with gales for
the central and eastern strait...so have upgraded inherited gale
watch into a warning...as well as putting out some associated SCAs
to go with it. A Puget Sound Convergence Zone will develop around
north Seattle and Kingston this evening. Moderate onshore flow will
then continue on Sunday and Sunday night.

High pressure and weaker winds will prevail on Monday and Tuesday.
A front should move across the waters on Tuesday night, followed by
onshore flow next Wed. Haner/SMR

&&

.HYDROLOGY...River flooding is not expected for the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until noon PDT today 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.

     Small Craft Advisory until 9 AM PDT this morning for Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-Coastal
     Waters From James Island To Point Grenville Out 10 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater Out
     10 Nm.

     Small Craft Advisory from 2 PM this afternoon to 7 PM PDT this
     evening for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from 7 PM this evening to 3 AM PDT Sunday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 6 PM this evening to 6 AM PDT Sunday
     for Admiralty Inlet-Northern Inland Waters Including The
     San Juan Islands.

     Small Craft Advisory from 5 PM this afternoon to 2 AM PDT Sunday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.

&&

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html