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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 191010

Area Forecast Discussion
National Weather Service Seattle WA
310 AM PDT Tue Mar 19 2019

.SYNOPSIS...A strong upper level ridge and offshore flow will give
a couple more sunny and very warm days to Western Washington.
Record highs will likely be broken across the area again today and
on Wednesday. Offshore flow will weaken on Thursday resulting in 
cooler temperatures and an increase in cloud cover. A weakening 
front will spread northeastward across the area on Friday bringing
some light rain to the region. There will be a chance of showers 
next weekend with near normal temperatures.


500mb ridge centered over central portions of British Columbia
will drop slowly southeastward into Montana on Wednesday then 
will finally move SE into the central plains on Thursday. Strong 
offshore flow will continue today through Wednesday, then will 
relax on Thursday as the upper ridge and its associated surface 
center weaken and pull away from the area.

Sunny days and clear nights will prevail through Wednesday. Highs
both today and on Wednesday will be quite warm with the easterly 
flow and strong sunshine. Most areas will be in the 70s today. The
coast will likely see a few degrees of cooling on Wednesday, but 
the interior will likely see another day in the lower to mid 70s.
Record high temperatures will be easy to obtain today as previous
records are in mainly in the mid 60s. Record highs for Wednesday
should also be within easy reach. 
Lows this morning and Wednesday morning will be dependent on 
exposure. Locations like Seatac Airport and Renton -where 
easterly flow out of Snoqualmie Pass is unhindered- will have 
difficulty dropping below 50 degrees. Protected river valleys in 
the south interior will fall to around 40. 

As offshore flow decreases Wednesday night into Thursday, expect a
weak southerly surge to develop over the Oregon coast and lift
northward into the area. This will give some late night and
morning stratus to the coast and portions of the interior and will
result in lows dropping more uniformly into the 40s. Isolated
showers or light drizzle is possible on portions of the Olympic
Peninsula Thursday morning. Albrecht

.LONG TERM /FRIDAY THROUGH MONDAY/...00Z model solutions continue
to show the arrival of a negative tilt frontal system Friday
afternoon that will be followed by a chance of showers into
Saturday. The ECMWF shows a minimum of shower activity on Sunday
as low level offshore redevelops while the GFS shows some shower
activity associated with a weak upper low persisting into Sunday.
A model blend that is weighted toward the ECMWF was used in the
forecast for now. Another negatively tilted frontal system will
approach the area from the southwest Monday or Monday night. With
the increase in clouds and moisture along with decreased offshore
flow through the extended forecast period, expect temperatures to
average closer to normal for late March. Albrecht


.AVIATION...A strong upper level ridge will remain over western
Washington today, with low level offshore flow persisting 
throughout the day. Overall current conditions at the terminals 
are VFR across the board. The air mass remains dry and stable, 
with southeasterly flow aloft. Easterly surface winds are 
expected to pick up for terminals near the southern portion of 
the Sound near 18Z.

KSEA...East-southeasterly winds 5-15 knots. A lull in winds is 
expected early this morning, with winds picking up again near 18Z.
VFR conditions. 14


.MARINE...Offshore flow will continue with surface high pressure 
east of the Cascades. Breezy winds near the gaps in coastal terrain. 
Strongest east wind is expected to be at the West Entrance of the 
Strait of Juan de Fuca. Offshore flow will continue into tomorrow 
before easing middle of the week with the return of fronts later 
this week.


.HYDROLOGY...River flooding is unlikely over the next seven days.


PZ...Small Craft Advisory until noon PDT today for Coastal Waters 
     From James Island To Point Grenville 10 To 60 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 8 PM PDT this evening for Central 
     U.S. Waters Strait Of Juan De Fuca-Coastal Waters From Cape 
     Flattery To James Island Out 10 Nm-West Entrance U.S. 
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 2 PM PDT this afternoon for Coastal 
     Waters From Cape Flattery To James Island 10 To 60 Nm.