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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 190401

Area Forecast Discussion
National Weather Service Seattle WA
901 PM PDT Thu Apr 18 2019

.SYNOPSIS...Showers to continue through Friday as a frontal system
moves through the area. Dry weather and warmer temperatures are
expected over the weekend into early Monday. Another system will
bring rain later Monday into mid-week.


.SHORT TERM /TONIGHT THROUGH SUNDAY/...Continued showers across
the area this evening, due to a frontal system offshore, has 
brought decent rainfall amounts over the last 12 hours along the 
coast and north Sound. Bellingham has recorded a half an inch over
the last 12 hours. Totals elsewhere have generally ranged from a 
few hundredths around the central and southern Sound to near 
three quarters of an inch across the mountains. A cold front will 
move across the area tonight into Friday bringing more steady 
rainfall. A few post-frontal showers into Friday afternoon with 
the possibility of a convergence zone over Snohomish/King Counties
with the return of onshore flow. This activity is expected to 
wind down toward the evening.

A ridge will build into the area Friday night and continue through
early Monday. Expect mainly clear skies with warmer temperatures
for holiday activities through the weekend! Temperatures on 
Saturday will generally be in the upper 50s to low 60s with 
temperatures a few degrees warmer on Sunday in the low to mid 60s 
across the area. 

.LONG TERM /MONDAY THROUGH THURSDAY/...As mentioned by previous
shift, models slowed down the arrival of next frontal system on
Monday. Still, differences remain between GFS and ECMWF solutions. ECMWF
stalls the wave offshore, leaving most of the area dry through 
Tuesday night. GFS has showers arriving Monday night into Tuesday 
with secondary wetter wave on Wednesday. For now, have cut back 
precipitation changes until later in the day Monday and will 
continue to monitor solutions. Past Wednesday, looks like ridging 
will return for the end of the week. CEO


.AVIATION...A frontal system will reach the coast tonight and
dissipate over the area Friday. Flow aloft will remain west to
southwest. The air mass is moist and stable. At the surface,
moderate southerly flow tonight will become moderate onshore late
Friday afternoon. Ceilings generally VFR currently with MVFR/IFR
during times of rain along coast and far north Sound. Showers will
be spotty tonight, becoming more widespread early Friday with the
frontal passage. Expect CIGs to become MVFR by 08z with MVFR
through Friday as the front works its way through the region.
Pockets of IFR are possible tonight, especially across the north
Sound and along the coast.

KSEA...VFR cigs will become MVFR tonight as the front pushes
through. Showers mainly spotty tonight becoming more widespread
Friday morning. Winds generally southerly 5-12 knots. JD


.MARINE...A weak front will reach the coast tonight and dissipate
over the area Friday. Strong onshore flow may develop behind the
front Friday night, with gales possible in the strait. A gale
watch is in effect Friday night for the strait. 

High pressure offshore over the weekend with lower pressure inland
will diminish onshore flow. A frontal system is expected to reach
the area on Monday.


.HYDROLOGY...Rivers coming out of the North and Central Cascades 
will rise significantly later today through Friday but are 
expected to remain below flood stage. River flooding not expected 
across the area for the next 7 days. JBB


PZ...Small Craft Advisory for hazardous seas until 5 AM PDT Friday 
     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.

     Small Craft Advisory for rough bar from 2 AM to 8 AM PDT Friday 
     for Grays Harbor Bar.

     Gale Watch from Friday afternoon through late Friday night for 
     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 Admiralty 
     Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca-West 
     Entrance U.S. Waters Strait Of Juan De Fuca.