FXUS66 KSEW 190941
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
241 AM PDT Thu Sep 19 2024

.SYNOPSIS...Weak high pressure holds over the region through
Thursday with morning clouds but afternoon sunshine. Expect a
return to a wetter pattern Friday and again late in the weekend as
the next disturbance crosses the region.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...Western WA remains under
the influence of onshore flow for slightly cooler weather today -
highs tracking a degree or two below average. There is a
disturbance rolling through southern B.C. but we remain dry for
the most part (aside from a few light showers in the Cascades). A
weak ripple may help generate a few more showers in the interior
and Cascades on Friday. The next incoming frontal system pushes
into B.C. and stalls as we move into Saturday, keeping western WA
mainly dry. The air mass will be a little warmer with temps
tracking closer to average. 33

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Wetter weather is ahead as
we move into later Sunday and Monday, especially for the coast and
mountains with a steady stream of moisture over the region.
Ensemble guidance is backing off on total rainfall amounts in the
interior (Seattle south) with a 25-50% chance of seeing
measurable rain. But there's a good chance of wetting rains at the
coast and mountains with 0.25-0.50" ranges. Moving on, we're on
the northern edge of a ridge as it moves inland on Tuesday. This
results in a dry and warmer pattern with highs in the 70s again.
Then, toward midweek, moist SW flow returns as the ridge moves
farther inland. This brings cooler and wetter weather back to
western WA with a chance of rain. 33

&&

.AVIATION...An upper ridge centered well offshore and an upper
trough moving into British Columbia today will produce increasing
northwesterly flow aloft over Western Washington. Widespread low
level moisture remains in place across the area this morning
producing a mixed bag of ceilings. Areas of IFR/MVFR ceilings and
localized LIFR will persist this morning before lifting to VFR
across interior areas 18Z-20Z. Increasing low level onshore flow
later today is expected to spread low MVFR stratus across much of
the lowlands of Western Washington on Friday morning.

KSEA...Multiple cloud decks complicating the forecast picture this
morning. But overall, expecting IFR ceilings to develop by around
sunrise with some tempo LIFR between 14Z-16Z. Ceilings will
gradually lift back to VFR by 19Z-20Z. Ceilings will deteriorate
again by Friday morning with low MVFR or IFR in stratus. Surface
winds light and variable early becoming southwesterly 5 to 8 knots
late morning through the evening. 27

&&

.MARINE...Broad surface ridging will remain centered well offshore
into the weekend. Onshore flow will increase tonight into Friday as
a system moves by well to our north. Small craft advisories have
been posted for the outer coastal waters and the central/east
portions of the strait. Surface ridging expands in the coastal and
interior waters on Saturday for lighter winds. A series of weak
frontal systems will brush the area early in the coming week, but
are presently not expected to produce any headlines. 27

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 5 PM this afternoon to 3 AM PDT Friday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 11 PM this evening to 5 PM PDT Friday
     for Coastal Waters From Cape Flattery To James Island 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     10 To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm.

&&

$$