FXUS66 KSEW 021021

Area Forecast Discussion
National Weather Service Seattle WA
221 AM PST Sat Mar 2 2024

.SYNOPSIS...A broad upper level trough will maintain cool and
showery conditions across Western Washington into early next week.
A weak upper level ridge is expected to lead to somewhat drier
conditions by the middle of the week. Temperatures will remain
below normal.


.SHORT TERM /TODAY THROUGH MONDAY/...The next in a series of
several disturbances embedded within the upper level trough
offshore is spreading showers across the region early this
morning. The air mass remains quite cool with snow levels running
between 500 and 1000 feet. Much like yesterday, dew points
remain mostly in the mid to upper 30s. Combined with low level
south/southeasterly flow, this will limit the potential for any
snowfall accumulation for the lowlands. Temperatures remain cold
aloft...-35 to -38 C at 500 millibars. And with that will come
continued instability for isolated thunderstorms, particularly
near the coast.

The pattern remains in place through the weekend with periodic
increases in shower activity as impulses rotate onshore. Another
upper trough digging southward down the British Columbia coast
keeps the unsettled cool pattern in place heading into Monday.
There may be a modest increase in shower coverage with this
feature as it rotates onshore. Temperatures throughout the short
term forecast period will be several degrees below normal...more
typical of early January than the first week of March.

.LONG TERM /TUESDAY THROUGH FRIDAY/...Models generally remain on
board with finally bringing the upper trough axis onshore and
shifting it east of the Cascades by later Tuesday for decreasing
showers. By the middle of the coming week, low amplitude upper
ridging is expected to build well offshore. This would put the
region in cool, northwest flow aloft. It`s not an entirely dry
pattern as the potential remains for the region to get clipped by
a pair of frontal systems moving into British Columbia. However,
ensembles are fairly confident that much of the area could string
together a couple of mostly dry days with temperatures gradually
moderating to near or slightly below normal. 27


.AVIATION...An upper trough remains offshore today and Sunday,
maintaining generally southwest flow aloft. A weak surface low is
brings a focus of showers across the region early this morning
followed by a brief lull before another one crosses later in the
day. Expect mostly lower VFR ceilings during the breaks in between,
but the precipitation may be heavy enough to bring low MVFR ceilings
and restricted visibilities in rain. Local IFR is possible near the
coastal terminals. Thunderstorm chance remains quite low, generally
around 15% or less, but cannot be ruled out near the coast and into
the Puget Sound region by late afternoon.

KSEA...Mostly VFR ceilings through the day today with round of rain
through 13z and again 22-04z bringing the best chances for MVFR
conditions. Around a 15% chance of a strong shower producing
lightning during the second window, but confidence remains low.
Winds should remain southerly for the majority of the day, though
gusty and shifting winds will be possible under any strong showers
or thunderstorms.


.MARINE...Low pressure remains in place offshore with numerous low
centers developing and moving north through the coastal wasters
through the weekend. These will cause shifting wind directions as
they pass and expected continued showers through the weekend with
gusty winds at times. The small craft advisory for the coastal
waters has been extended through the day today with seas likely
hanging on in the 10-12 ft range over most of the coastal waters
before gradually subsiding. Another more organized low approaches
late in the weekend, but significant impacts aren`t expected at this
time. High pressure then begins to develop toward mid-week which
will preclude significant marine weather impacts.


.HYDROLOGY...Showers will remain likely at times throughout the
weekend. The Chehalis river at Porter is cresting, while the
Chehalis at Grand Mound has crested and will continue to decrease.
Other area rivers will continue to recede throughout the weekend.
No additional river flooding concerns are present through at
least mid week. 14


PZ...Small Craft Advisory until noon PST today for Grays Harbor Bar.

     Small Craft Advisory until 10 PM PST this evening for Coastal
     Waters From Cape Flattery To James Island 10 To 60 Nm-
     Coastal Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     Out 10 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville
     To Cape Shoalwater Out 10 Nm.



NWS SEW Office Area Forecast Discussion

Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather