National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KSEW 091623
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
923 AM PDT Tue Apr 9 2024

.SYNOPSIS...Showers linger in a Puget Sound Convergence Zone into
the day, but otherwise a break in the weather with an upper ridge
developing over the region. This will bring warmer and drier
conditions through the middle of the week. Another cooler and more
active weather system then returns late in the week.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...We`re in post-frontal
onshore flow this morning with showers mainly within the
convergence zone over the interior and central Cascades. Showers
with the convergence zone will be diminishing this afternoon as
onshore flow weakens (and coastal winds turn northerly).
Additional snow amounts in the Cascades will be light and mainly
over the higher peaks - the Winter Weather Advisory has been
cancelled. 33

Previous discussion...Widespread rain and gusty southerly winds
continue across the region ahead of the advancing cold front.
Temperatures also remain rather mild, in the upper 40s to lower
50s, with the region mostly in the warm sector of the frontal
system and the atmosphere remaining well mixed given the winds.
Have continued the ongoing Winter Weather Advisory for the
Cascades for now, but with the snow level remaining fairly high,
expect that any impacts will be confined to those engaging in
activity in the high Cascades rather than impacts to travel.
Expect the heaviest precipitation rates in the next few hours this
morning as the front sweeps across the interior, as well as
potentially in a Puget Sound Convergence Zone that develops later
today. Otherwise, expect showers to begin to taper into the
afternoon as heights begin to rise and upper level high pressure
builds. This will bring about a warming and drying trend through
Wednesday, though the clearing skies will likely bring a much
cooler nights with the temperature dipping into the lower or mid
30s with the coolest spots away from the cities and water.

Another weak disturbance may clip the region on Thursday, enough
to bring a return of rain across much of the region. That said,
this system likely brings little if any measurable rain to the
interior and only a bit (less than a quarter inch of rain) to the
coastal areas, so the bigger impact will be additional cloud cover
for most of the area.

.LONG TERM /FRIDAY THROUGH MONDAY/...Ensemble guidance continues
to favor the next disturbance remaining offshore and dipping to a
position off the California coastline. This would bring a return
to a more zonal flow pattern across the area, with some clusters
of guidance even boosting heights further. This will keep
temperatures near to slightly above normal for the end of the week
(Friday and Saturday) along with likely dry conditions, though
some low end rain chances do return. Snow levels remain around
5,000 feet or higher for Friday and Saturday, which should
preclude any travel impacts in the Cascades. Confidence remains
lower for the start of next week, with a fairly even split among
ensemble guidance suggesting the potential for a cool trough or a
continuation of the drier and warmer pattern. Will need to keep an
eye on this evolution as some of the cooler and more active depictions
would bring the potential for snow levels to dip to near or below
the Cascades passes by Monday.


&&

.AVIATION...West to northwest flow aloft is expected over Western
Washington today in the wake of a cold front that moved across the
region early this morning. Areas of IFR/MVFR in the vicinity of some
post-frontal convergence around Puget Sound will lift to VFR near or
after 21Z as a low amplitude upper ridge builds into the area. VFR
will prevail on Wednesday with the exception of some patchy IFR in
morning stratus/fog over south Puget Sound.

KSEA...Post-frontal convergence will gradually dissipate well north
of the terminal by early afternoon. MVFR ceilings will lift to VFR
near or after 20Z. Surface winds W/SW 7 knots or less will gradually
veer to northwesterly late this afternoon then become light N/NE
overnight. 27

&&

.MARINE...Surface ridging will build into the coastal waters today
and tonight before shifting inland on Wednesday. A weak frontal
boundary will reach the waters on Thursday, but is not presently
expected to require any headlines. Broad surface ridging rebuilds
over the coastal/offshore waters late this week with lower pressure
remaining east of the Cascades. This will produce generally light
onshore flow heading into the upcoming weekend. 27

&&

.HYDROLOGY...No river flooding is expected over the next seven
days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 8 PM PDT this evening 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 AM PDT this morning for Admiralty
     Inlet.

&&

$$