Preview of NWS' New Version of Forecast
This preview is not operational and should not be used for support decisions.

Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 222221

Area Forecast Discussion
National Weather Service Seattle WA
330 PM PDT Sun Sep 22 2019

.SYNOPSIS...Showers will taper tonight. A weak ridge will build over 
the area Monday, with the next system moving through the ridge 
Monday night into Tuesday. Another system arriving Wednesday night 
into Thursday will bring considerably cooler conditions.


tonight. A convergence zone seems probable, setting up in Snohomish 
County late this afternoon, then moving south into King County this 
evening. Monday will start dry, with only scattered showers in the 
morning, but a weak impulse in moist northwest flow aloft will 
enhance showers on the coast in the afternoon, and elsewhere 
overnight into Tuesday. Some clearing is likely Tuesday afternoon. 
Highs will be in the low to mid 60s Monday, and in the mid to upper 
60s Tuesday.

Showers will taper again Tuesday night, with much of Wednesday 
looking dry. A wet system will arrive from the northwest Wednesday 
afternoon, spreading rain to all areas Wednesday night. Highs will 
range from the low 60s north to the upper 60s south. Burke

.LONG TERM /THURSDAY THROUGH SUNDAY/...The system Wednesday night is 
associated with a deep upper trough, with heights the lowest they 
have been since...spring?  The snow level will fall to 5000 feet or 
lower. The trough will be over Washington on Friday, with even lower 
heights. The upshot is there will be snow in the mountains, possibly 
in the higher passes, and temperatures will struggle to get above 60 
on Friday and Saturday. Some improvement is possible Sunday, but 
temperatures will still be on the cool side. Burke


.AVIATION...Southwesterly flow aloft will become more northwesterly
this evening as an upper level trough moves through the region. 
The surface front has moved inland and will continue to move 
through the remainder of the area this afternoon. This will 
continue to bring widespread MVFR/IFR conditions to the terminals.
Current radar imagery has showers moving across much of the 
Sound, with the heaviest areas of precipitation generally across 
the southern portion of the Sound. A few spots could improve back
to VFR conditions by later this evening in the wake of the 
frontal passage, however it's more likely that conditions will 
remain MVFR for most terminals throughout the evening hours. A 
convergence zone may develop in the vicinity of King/Snohomish 
Counties later this afternoon into this evening, which would keep 
cigs MVFR/IFR for terminals in its vicinity. Winds will generally 
be southerly 5 to 10 knots for areas inland, with northwesterly 
winds 10 to 15 knots along the coast. A few higher gusts will be 
possible in the vicinity of the front or in areas of heavier
showers. SB

KSEA...Current conditions are MVFR. Expect conditions to continue
through the evening hours, especially if a convergence zone
develops across King and Snohomish counties. Conditions could
become IFR near any bands of heavier precipitation. Winds generally
southerly 5 to 10 knots. SB


.MARINE...A front has moved inland today, bringing small craft 
advisory northwesterlies to the coastal waters in its wake. A 
Small Craft Advisory is also in effect for westerlies across the 
Strait of Juan de Fuca this afternoon and evening. As a result, small
craft northwesterlies could bleed into the adjacent Admiralty 
Inlet waters and small craft southwesterlies could bleed into the
Northern Inland waters. Winds will then ease Monday morning with 
another frontal system moving through the area Monday afternoon. 
This system will likely bring another round of small craft 
advisory winds to the coastal waters and portions of the inland 
waters. SB


.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
until then.


PZ...Small Craft Advisory until 2 AM PDT Monday 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 5 AM PDT Monday for Central U.S. 
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters 
     Strait Of Juan De Fuca.

     Small Craft Advisory until 8 AM PDT Monday for Northern Inland 
     Waters Including The San Juan Islands.

     Small Craft Advisory until 11 PM PDT this evening for West 
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 6 PM this evening to midnight PDT 
     tonight for Admiralty Inlet.