Small Craft Advisory 57, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
230 AM PDT Wed Mar 15 2017

.SYNOPSIS...A frontal boundary draped across Western
Washington this morning will lift northward before being pushed
eastward later today. Snow levels will decrease tonight and
precipitation will turn showery. A weak front will arrive on
Thursday before a stronger front brings additional rain and wind
early in the weekend. Drier weather is possible Sunday and Monday.

&&

.SHORT TERM...A wave traveling along a frontal boundary draped
across Western Washington will bring another round of moderate to
heavy rain...especially across the southern two thirds of the
forecast area. By later this morning, Seattle will pass its normal
monthly precipitation total for March. Additionally, there is a high
probability that Seattle will pass the normal water year
precipitation total (normal is 37.49" Oct 1-Sep 30) before the end
of the day. There are flood watches over Lewis and King counties for
a couple of rivers and flooding warnings are already in effect for
the White and Skokomish Rivers. The threat for increased landslides
also continues. See the HYDROLOGY section below for more information.

The front will move east by this evening with rain turning to
showers and snow levels lowering to some pass levels by Thursday
morning. Onshore flow increases tonight and it should be breezy or
locally windy this evening both in the Strait and Puget Sound areas.
A weak front will bring some light precipitation to the area on
Thursday. Most of the QPF with this front is expected on Olympic
Peninsula with just spotty stuff over the interior. The models
appear to be slowing down the timing of the stronger system for the
first part of the weekend. The GFS and Euro disagree on the track
and strength of the associated surface low, but seem to agree on
keeping much of the interior dry on Friday with rain and potentially
windy conditions developing Friday night.

.LONG TERM...Post frontal showers will linger through Saturday or
early Sunday before ridging starts to build into the region. The
first day of Spring looks pleasant with some offshore flow and
partly to mostly sunny skies. The 00Z GFS keeps us dry into
Wednesday while the Euro is more agressive with spreading some
precip back into the area on Tuesday. Perhaps a little collective
wishcasting by the locals will nudge the models toward agreeing on a
dry stretch longer than 24 hours. 27

&&

.AVIATION...Southwest flow aloft, the air mass is moist and stable.
Rain from a frontal system at 2am was mainly south of a line from
Seattle to Hoquiam, but this front will lift north through the
morning hours and then shift inland as a cold front this evening.
There are a hodge podge of conditons early this morning, owing to
the moist air, the light winds, and the stable air mass. Later today
as the cold front moves through the area cooler drier air will
finally arrive and Thursday looks like it could be a nice break
between weather systems.

KSEA...Rain this morning as a front shifts north into Western
Washington. The cold front will shift inland this evening. There
will be a push of southerly flow this evening.

&&

.MARINE...Gradients will be light until an increase in onshore flow
later this afternoon and evening as a cold front moves through the
area. The frontal system is shifting north into Western WA early
this morning and then late this afternoon and evening it will
finally move inland. There will be a push of southerlies up Puget
Sound this evening with Westerlies developing coast and Strait.
Thursday looks like a break between systems. A stronger low pressure
system will reach the area Friday night and the associated cold
front pushes in to the Cascades by noon Saturday with a decent push
of westerlies coast and Strait on Saturday.

&&

.HYDROLOGY...The Skokomish River in Mason County is above flood
stage; minor flooding is expected there. There is also a flood
warning in effect for the White River near Pacific. Flow at the R
Street Bridge in Auburn is forecast to reach about 6000 cfs tonight,
which would cause flooding in Pacific. The central and south
Cascades are forecast to receive the most rain through Wednesday. A
flood watch is in effect for the Cowlitz in Lewis County, and the
watch includes King County for possible minor flooding on the
Snoqualmie River system.

A series of weather systems moving through the area this week will
keep a threat of landslides. A special weather statement addresses
this. Burke

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch through Wednesday afternoon for King and Lewis
     counties.

PZ...None.

&&

www.weather.gov/seattle

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