Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 301652
Area Forecast Discussion
National Weather Service Seattle WA
900 AM PDT Thu Mar 30 2017
.SYNOPSIS...An upper level trough over the region will shift
eastward today. High pressures building over the region tonight and
Friday will provide dry and slightly warmer weather. A weak front
will bring some light rain on Saturday with a lingering trough
providing a chance of showers on Sunday. Somewhat drier conditions
Monday could be followed by more rain with another front by the
middle of next week.
.SHORT TERM...Radar indicates showers continue streaming into Wrn Wa
this morning under moist northwest flow. A residual convergence band
of showers is also evident over Snohomish and parts of King county,
although this appears to be less organized and should dissipate over
the next few hours. The overall trend today is for decreasing
showers as the 500 mb trough axis moves east of the region. Visible
imagery shows some breaks in the clouds offshore and as moisture
decreases this afternoon, some sunbreaks should also develop over
parts of interior Wrn wa. It will remain cool today with highs only
in the low 50s.
High pressure aloft build over the Pacific Northwest tonight and
Friday. Models shows some high level clouds breaking over the ridge
some there may be filtered sunshine with mostly sunny in the
forecast maybe a little optimistic. But it should be dry with high
temperatures about +5 degrees from today, possibly reaching near 60
around the southwest interior and parts of greater Puget Sound
inland from the water.
The next system will approach Friday evening with thicker mid and
high clouds developing over the area. A weak front will cross Wrn Wa
on Saturday with some spotty light rain across most the area.
Nothing heavy but enough to measure across much the area. The
onshore flow will also hold back high temperatures, with mostly
upper 50s but possibly a couple 60s in the south interior. Mercer
.LONG TERM...Previous discussion...Much of Western Washington could
get away with a dry day on Sunday, but the presence of a trough
overhead is enough to keep a chance of showers in the forecast. Both
the GFS and Euro bring more ridging to the area Monday into Tuesday.
Current forecasts have chance PoPs for that period, but those could
be trimmed back or eliminated if the models continue with that trend.
A return of more wet and unsettled conditions is possible by the
middle of next week as the models show a broad upper level trough
digging into our offshore waters with a series of systems moving
.AVIATION...Northwesterly flow aloft, low level westerly flow
with high pressure to the west and low pressure inland. The air is
moist and somewhat unstable with scattered showers. Morning low
clouds and widespread bkn-ovc cigs will lift and break up into sct-
bkn cumulus in the afternoon. The mountains will likely remain
mostly obscured through the day.
KSEA...Conditions will improve through the day as the clouds lift in
standard springtime fashion. The wind should be light and variable
with the metro area in an area of converging winds.
.MARINE...Westerly flow coastal waters and Strait of Juan de Fuca
today. The winds will be convergence zone winds for Puget Sound, and
there will also be convergence up through the San Juans. As the high
pressure builds in tonight winds will become fairly light through
Friday. A weakening front will reach the coast around daybreak
Saturday--it looks pretty weak in the 12z nam fcst.
.HYDROLOGY...The Skokomish river in Mason county fell below flood
stage around 6 am PDT this morning. This trend will continue and the
flood warning will likely be dropped with the next update prior to
noon today, assuming the rapid fall continues.
No other really strong and wet systems are expected for the next
week so flooding is not expected on area rivers during the next 7
The heavy rain did increase the threat of landslides across W WA
again. Any additional light showers today will have little or no
impact on the risk of landslides. While the immediate high risk of
landslides is decreasing, soils are generally still saturated from
wet weather this past month. The risk of landslides will remain
PZ...Small Craft Advisory until 5 PM PDT this afternoon 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 for rough bar until 11 PM PDT this evening
for Grays Harbor Bar.
Small Craft Advisory until 5 AM PDT Friday for Admiralty Inlet-
Central U.S. Waters Strait Of Juan De Fuca-East Entrance
U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory until 11 PM PDT this evening for West
Entrance U.S. Waters Strait Of Juan De Fuca.
You can see an illustrated version of this discussion at