Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 191030
Area Forecast Discussion
National Weather Service Seattle WA
330 AM PDT Wed Apr 19 2017
.SYNOPSIS...A slow moving front offshore will move through the
area later this afternoon into the evening hours followed by an
upper level trough on Thursday. An upper level ridge will build
over western Washington on Friday. The break in the weather will
be brief with weak weather systems arriving Saturday and Sunday. A
stronger system is timed into the area on Monday.
.SHORT TERM...Satellite imagery shows mostly cloudy skies over
Western Washington early this morning with most of the cloud
cover high clouds. The potential is there for a colorful sunrise.
Doppler radar has the leading edge of the rain out ahead of the
next system along the North Coast but still offshore along the
Central Coast. Temperatures at 3am/10z were in the 40s.
Nothing new in the 00z model runs. Front offshore already parallel
to the upper level flow. In addition to being parallel to the
upper flow there is also a wave moving up the backside of the
front west of Hoquiam. Both of these factors will cause the front
to only move slowly eastward this morning. Rain out ahead of the
front will spread over the entire coast in the next few hours but
with the lack of any real eastward movement the rain will have a
hard time getting much farther than the Puget Sound by 18z. Upper
level trough currently near 140w will kick east later today and
that will help push the front east with the front near the
coastline by 00z Thursday. Rain spreading over the remainder of
the area this afternoon. With the increasing rain and cloud cover
it will be hard to get much more than 10 degrees or so of heating.
This puts highs in the 50s. A couple of degrees below normal.
Front moving through Western Washington this evening with the
steady rain changing to showers. Some breaks in the cloud cover
early Thursday morning will allow lows to drop back into the 40s.
Upper level trough offshore becoming negatively tilted tonight.
The trough will move inland on Thursday. Convective variables are
very similar to Tuesday`s numbers with lifted indexes near 0, 500
mb temperatures near -30C and convective temperatures in the
lower 50s in the afternoon. This will keep a slight chance of
thunderstorms in the forecast for Thursday afternoon in addition
to the shower activity. Highs will be in the 50s.
Upper level ridge building offshore will the upper level trough
east of the area Thursday night. Shower activity will dry up
quickly in the evening with the possible exception of over
Snohomish county with a convergence zone.
Upper level ridge moving over Western Washington on Friday with
500 mb heights rising to around 570 dms. Temperatures aloft warm
but are not very impressive with 850 mb temperatures by 00z
Saturday around plus 5C. Model sounding do show easterly winds
right off the ground all the way up to 700 mb. This offshore flow
will help warm temperatures up into the 60s Friday afternoon with
the warmer locations pushing 70 degrees.
.LONG TERM...As has been the case since October the dry spell
will be short lived as the upper level ridge shifts east Friday
night with yet another negatively tilted front moving into the
area on Saturday. Upper level trough moving through Western
Washington Sunday with a much more consolidated front reaching
the area Monday. Broad upper level trough over the area on
Tuesday with Western Washington on the cold side of the jet
keeping a chance of showers in the forecast. Multiple runs in a
row of the extended model solutions have had this scenario for the
weekend into the first part of next week. Felton
.AVIATION...An upper trough is offshore and that will continue to
give the region southwesterly flow aloft. There is a front just off
the coast early this morning and that will slowly move through
Western Washington today. Early this morning a lot of the clouds
have scattered out and there were only some high clouds, but as the
front comes ashore clouds will increase, cigs will drop, and the
mountains will become mostly obscured again.
KSEA...There were only high clouds early this morning, but as a
front arrives today clouds will increase pretty quickly with rain in
the afternoon and lowering cigs later in the day.
.MARINE...A front will bring small craft advisory winds to the
coastal waters, entrances to the Strait of Juan De Fuca and the
northern waters. Onshore flow will prevail behind the front
Wednesday night and Thursday as high pressure builds in from the
southwest. The high pressure will shift inland Thursday night and
Friday for a period of offshore flow. Another front will arrive on
.CLIMATE...Record rain in Seattle on Tuesday with 0.48 inches
breaking the old record of 0.40 inches set in 1970. Tuesday`s
record rain was the second lowest daily record rain value in the
month of April. The only day with a lower record daily rain in
April is the 26th with 0.37 inches. The 0.48 inches in Seattle
puts the monthly rain total at 2.92 inches surpassing the normal
for the entire month of 2.71 inches. The record for the wettest
April in Seattle is 6.53 inches in 1991. Since records started
in the Seattle area in the 1890`s there have only been three
Aprils with 5 inches plus of rain, 6.53 in 1991, 5.89 in 2013 and
5.37 in 1996. Felton
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 9 PM PDT this evening for East
Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
Waters Including The San Juan Islands.
Small Craft Advisory until 4 PM PDT this afternoon for Central
U.S. Waters Strait Of Juan De Fuca-West Entrance U.S.
Waters Strait Of Juan De Fuca.
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