Navigation

External Links

Alerts


No alerts 
543
FXUS66 KSEW 030403
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
801 PM PST Mon Dec 2 2024

.SYNOPSIS...High pressure will continue to amplify into western
Washington through Tuesday, allowing for dry conditions and periods
of morning fog and low stratus. The upper ridge will weaken midweek
as the next storm system approaches, bringing in the next chance for
widespread precipitation across the region late week and into the
weekend.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...Current satellite imagery
shows most of the lowlands fraught with fog or low clouds, with many
obs reporting at least some form of visibility limitation. While
incoming upper level clouds would ordinarily serve to mitigate this
fog formation, the fact that said fog is already in place coupled
with narrow...if existent at all...temp/dewpoint spreads will likely
keep these conditions in place overnight and throughout Tuesday
morning before some clearing and lifting occurs in the
afternoon...potentially. Like 24 hours ago, models continue to
advertise clear skies emerging areawide in the afternoon, however
may need to espouse a wait-and-see mentality. Needless to say, at
the very least the Tuesday AM commute will likely be impacted.

Inherited forecast looks good and is on track, thus no need for any
evening updates. For additional forecast details, please refer to
the Previous Discussion section below.

18

High pressure remains in control through Wednesday for an extended
period of dry and stable conditions. Light winds and poor mixing is
leading to stagnant conditions in the interior where low clouds and
fog linger. As a result, temperatures remain cool and in the 30s and
40s. It`s sunny up in the mountains, though. Low clouds will settle
again overnight with dense fog possible for the Tuesday morning
commute. Freezing fog is also possible, especially around the south
sound. A trough will override the ridge on Thursday with a period of
light rain. Winds and mixing will also increase, helping to scour
out the low level air mass. 33

.LONG TERM /FRIDAY THROUGH MONDAY/...From Previous Discussion...A
warm front clips the area on Friday for rain and high elevation snow
(snow levels 7000-9000ft). Western WA is in the warm sector with
mild highs in the 50s. Low temps will also remain above freezing. A
baroclinic band shifts S/SE into western WA on Saturday for more
rain and heavier mountain rain/snow. Snow levels will lower to
around 3000-3500 ft by Saturday night. We`re under cool NW flow
Sunday and Monday with showers mainly impacting the Cascades (heavy
snowfall possible in the North Cascades). A ridge brings drier
weather moving into Monday, with a break in the precip noted in the
ensemble members. 33

&&

.AVIATION...Upper level ridging will keep light zonal flow aloft.
Surface winds largely light and variable except for HQM, where
easterly winds ranging 4 to 8 kts are in place.

Largely IFR/LIFR conditions in place over the majority of W WA this
evening and likely to remain that way into Tuesday afternoon. There
are some MVFR conditions in the San Juans, along the Strait,
and...oddly enough...in the SW interior. Expectation is to see
conditions erode further in these holdouts and should join remainder
of IFR/LIFR terminals tonight. Models remain persistent in wanting
to improve conditions in the late morning/early afternoon with clear
skies or at least VFR conditions in place by late afternoon/early
evening. Of course, they were advertising that 24 hours ago for
today, so a wait-and-see approach might be more valid here. The
window in which these VFR conditions will be in place provides
another forecast problem...as given both the weather pattern and
some of the newest 00Z data, a return to foggy conditions may be in
the cards for Tuesday night. To straddle the line, will likely
introduce a return to MVFR or IFR conditions for at least the
locations more prone to lower cigs.

KSEA...IFR cigs already in place this evening and will likely see a
return to LIFR conditions with fog tonight. Inherited forecast
proving to be a little more agressive with this timing than obs bear
out...so while the 06Z issuance may need to push this back a little
bit, overall trend in current TAF looks good. Still on track for an
afternoon break out, as per models...but given how Monday turned
out, it would not be wrong to meet this with a bit of skepticism.
However, solutions remain consistent and as such, will opt to keep
this in the forecast for now. Surface winds generally light with
speeds less than 5 kts. Will stick with northerly direction in
current TAF as models remain consistent in this direction, even if
obs seeming to favor variability.

18

&&

.MARINE...High pressure will remain situated over the Pacific
Northwest through midweek. This will lead to widespread fog and
limited visibility less than 1 NM possible. Waves will be
generally be between 5 to 8 ft over the coastal waters. A series of
weather systems will begin to impact the area on Thursday. A much
stronger system begins to move through on Friday that may lead to
waves between 10-15 ft along with stronger winds.

MGF

&&

.HYDROLOGY...From Previous Discussion...An upper ridge will remain
in place across Western Washington through Wednesday. A frontal
system will move through on Thursday for lighter QPF amounts.
Another weather system Friday into Saturday is forecast to bring
heavier QPF amounts. In addition, snow levels are expected to rise
later Friday into early Saturday to 7000 to 9000 feet. This,
combined with rainfall, will result in rises on rivers across
Western Washington. At this time, the Skokomish River is the main
river of concern for potential river flooding during this period.
However, other area rivers will need to be monitored due to the
higher snow levels Friday into Saturday. JD

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$

NWS SEW Office Area Forecast Discussion