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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

                            
000
FXUS66 KSEW 220435
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
835 PM PST Thu Feb 21 2019

.SYNOPSIS...Dry northerly flow will continue tonight. A frontal 
system will bring rain and mountain snow on Friday. A cool upper 
trough will follow the front for the weekend and into early next
week. Low snow levels will continue through the period.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...An upper ridge over the
area will shift inland tonight with increasing high clouds ahead
of an approaching frontal system. The aforementioned frontal
system and an associated upper trough will move into the area on
Friday bringing some rain and mountain snow. Snow levels will be
low enough for a possible rain/snow mix in some locations Friday
morning but this should transition to all rain by afternoon and 
no accumulations are expected. The mountains will likely pick up 
advisory amounts of snow. 

The front will be east of the area by Friday evening. Showers will
become mainly confined to the mountains, coast, and a Puget Sound
Convergence Zone Friday night. Snow levels will be low enough that
there might be some snow over the higher hills but accumulations,
if any, should be spotty and light. Some of the higher resolution
meso models hint at a little snow accumulation in the convergence
zone between Everett and Arlington Friday night but that is 
highly uncertain for now.

A broad upper trough will be over the area Saturday and Sunday
with continued low snow levels. Saturday looks like the more
showery day with most of the shower chances sagging south of the 
area on Sunday. Schneider

.LONG TERM /MONDAY THROUGH THURSDAY/...Previous 
discussion...Models are trending drier for the Monday/Tuesday 
period as our next system tracks south of the CWA. So even though 
snow levels will remain low, we are lacking the moisture and the 
threat for more lowland snow is decreasing. A wetter but warmer 
system may track north into Western Washington Tuesday night or 
Wednesday with rising snow levels and rain. It looks like 
temperatures will continue to moderate as we move toward the end 
of next week. Back to normal? 33

&&

.AVIATION...An upper ridge over the area will shift inland
tonight. An upper trough and an associated frontal system will 
move into the area from the northwest on Friday with increasing
westerly flow aloft. At the surface, southerly flow will increase
tonight and Friday morning as the front approaches and then turn 
westerly behind the front Friday afternoon. The air mass is dry 
and stable.

High clouds will increase tonight. Ceilings will lower Friday
morning with low clouds becoming prevalent by afternoon as a 
front arrives and rain moves into the area. 

KSEA...Clouds will increase and ceilings will lower later tonight
and Friday as a front arrives. Precipitation might start as a
rain/snow mix Friday morning but should transition to all rain by
afternoon. No accumulations are expected. Southerly winds will 
develop tonight and increase to 10-20 knots on Friday. Schneider

&&

.MARINE...A frontal system will move through the area on Friday
with small craft advisory southerly winds most waters. A weak
surface low near Queen Charlotte Sound Saturday morning will move
south to the Oregon coast by Sunday morning. Northeasterly
offshore flow will develop Saturday night and continue through
Tuesday with high pressure over British Columbia and lower
pressure to the south of Washington. Schneider

&&

.HYDROLOGY...River flooding is not expected for the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory from noon Friday to 6 AM PST Saturday 
     for Cascades of Pierce and Lewis Counties-Cascades of 
     Snohomish and King Counties-Cascades of Whatcom and Skagit 
     Counties.

PZ...Small Craft Advisory from 1 AM Friday to midnight PST Friday 
     night for Admiralty Inlet-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-Northern Inland Waters Including The San Juan Islands-
     Puget Sound and Hood Canal.

     Small Craft Advisory for hazardous seas until 8 PM PST 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 for rough bar until 9 PM PST Friday for 
     Grays Harbor Bar.

     Small Craft Advisory from 1 AM Friday to 4 AM PST Saturday for 
     East Entrance U.S. Waters Strait Of Juan De Fuca-West 
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 10 AM Friday to 4 AM PST Saturday for 
     Central U.S. Waters Strait Of Juan De Fuca.

&&

$$

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