Area Forecast Discussion Issued by NWS Seattle/Tacoma, WA
000
FXUS66 KSEW 190947
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
247 AM PDT Tue Mar 19 2024
.SYNOPSIS...A weakening upper level ridge will provide one more
dry and mild day for Western Washington on Tuesday. A weak upper
trough will produce some light precipitation across the region
later Wednesday into Thursday. A deeper trough and associated
frontal system will produce more widespread precipitation Friday
into the weekend along with snow levels falling to many of the
passes.
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.SHORT TERM /TODAY THROUGH THURSDAY/...Mostly clear skies prevail
across Western Washington early this morning as upper ridging
remains in control. The only exception is a shallow marine layer
along the central coast. Similar temperatures to Monday are
expected across interior areas today, but increasing onshore flow
will produce several degrees of cooling along the coast. The ridge
will weaken and shift eastward tonight as a weak upper trough
approaches the area. Clouds will increase and temperatures will
cool several degrees on Wednesday, but little in the way of QPF
is expected until Wednesday night when the trough shifts onshore.
A frontal system stalling offshore will spread additional light
precip across Western Washington on Thursday along with continued
cooler temperatures.
.LONG TERM /FRIDAY THROUGH MONDAY/...More significant
precipitation is expected to spread across the area on Friday as a
deepening upper offshore pushes a front onshore. Showery and
cool weather is expected over the upcoming weekend as the trough
gradually shifts onshore. Snow levels will creep downward as
well...likely to most of the passes by Saturday night into Sunday.
Unsettled conditions are likely to continue into the early part
of next week, but confidence is low in the details. Ensemble
means place the region in northwest flow aloft Sunday into Monday as
broad upper troughing takes up residence over the western lower
48. This leaves Western Washington susceptible to a system or two
slipping southward down the British Columbia coast. One thing is
for sure, the unseasonably mild and dry conditions aren`t
returning anytime soon. 27
&&
.AVIATION...Upper-level ridge overhead with southwest flow aloft.
Fog and low stratus currently hugging the coast as HQM is under LIFR
conditions. Most fog should remain here but can`t rule out patches
developing over parts of the interior as the morning progress.
Mostly VFR elsewhere throughout the day but, low stratus and fog
looks to spread further inland tonight with a better chance for
more widespread MVFR to LIFR ceilings and vis.
KSEA...VFR currently with light northerly winds at the surface.
Slight chance (15%) of LIFR fog between 12-16z this morning but VFR
should be at play most hours of today. Light winds at the surface
will increase out of the SW later this evening after 00z between 5-
10 kt as stratus draws near late overnight.
McMillian
&&
.MARINE...Onshore flow along with weak troughing at the surface.
Relatively benign conditions are expected today before a weak low
center enters tomorrow. However, no impacts are expected with sub-
advisory conditions likely. Seas less than 10 feet through the week,
mainly in the 3-6 ft range. A weakening front is probable to arrive
over the weekend with the next best chance of SCA winds over the
coastal waters.
McMillian
&&
.HYDROLOGY...No river flooding is expected over the next 7 days.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&
$$