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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSEW 251602
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
902 AM PDT Sat Mar 25 2023

.UPDATE...
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No changes to the current forecast. Broad upper level
troughing will continue to maintain shower activity through the
day today. Snow levels will rise above 1000ft by this afternoon
and combined with high temps in the mid and upper 40s, any threat
for winter weather will diminish.

A weak vort max will round the upper periphery of the broad trough
late this afternoon and into tonight and then swing across the
area. This will help maintain or even enhance shower activity
going into Sunday. Snow levels drop back down towards 500ft with
lows in the low-mid 30s overnight, which could make for areas of
a rain/snow mix or brief snow across the lowlands, especially on
the higher hills similar to last night. In addition to the winter
weather threat over the next 24 hours, broad troughing and
resultant cold mid level temps combined with sunbreaks and daytime
heating will make for a slight chance of thunder today,
especially near the Coast and south of Puget Sound.

Previous forecast discussion included below with an updated marine
and aviation section.

Kovacik
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&&


.PREV DISCUSSION... 
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/issued 333 AM PDT Sat Mar 25 2023/

.SYNOPSIS...A cool and active weather pattern will remain over
Western Washington through the weekend. Lingering cold
temperatures during the overnight and early morning hours may
bring a rain and snow mix both Saturday and Sunday. Drier and
warmer weather is in store early next week.
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&&

.SHORT TERM /TODAY THROUGH MONDAY/...The air mass over western WA
remains cool and showery with onshore flow and a deep upper level
low over the region. Temperatures are in the 30s this morning with
a few spots near freezing. Snow levels are low (only around
500-1000 ft) and there`ve been reports of a rain/snow mix in the
lowlands, especially within the convergence zone in King and
Snohomish counties. The convergence zone will be weakening this
morning but until then we will continue to see the threat of a
rain/snow mix. Overall, widespread and significant snowfall
accumulations are not expected. Snow will be tapering down in the
mountains too and the Winter Weather Advisory in the Cascades will
expire at 5 AM as planned. Otherwise, there`s still some moisture
and lift over the area for additional showers this afternoon.
Instability is greatest over southwest WA where there`s a slight
chance of thunderstorms. Temperatures will track cooler than
average with highs in the mid to upper 40s this afternoon.

Western WA is in between systems on Sunday but we`re still under
a broad trough that covers much of the West. There`s still a
little moisture and lift over the area but the overall consensus
in the ensemble guidance is that precipitation amounts will be
light - a few hundredths in the interior and less than 0.10" at
the coast. Cloud breaks will help nudge temps upwards with highs
near 50 although thats` still around 5 degrees cooler than
average.

Model ensemble guidance points toward drier weather as we move
through early next week. This is due to a strong system offshore
that shifts inland to our south on Monday. The low level flow
pattern will be turning offshore for less cloud cover. This will
help temperatures climb closer to normal with highs in the mid
50s. Morning lows will still be cool, though, and in the 30s. 33

.LONG TERM /TUESDAY THROUGH FRIDAY/...An upper low continues to
slowly spin to our south keeping western WA dry as we move through
Tuesday. We then see a ridge nudging inland Wednesday and Thursday
for warmer weather. Highs on Wednesday will be near 60 in the
interior with mid 50s along the coast. The ridge flattens and the
flow turns more zonal toward the latter half of the week with a
return toward wetter weather. 33

&&

.AVIATION...
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Light northerly flow aloft as an upper trough slides
across the Pacific Northwest today. Generally MVFR this morning with
areas of LIFR/IFR across portions of the southern Puget Sound,
mainly impacting KOLM/KCLS and KPWT. Some improvement to cigs to VFR
mid clouds later this afternoon. A few convective showers possible
this afternoon and this evening, with a slight chance of a
thunderstorm possible, mainly south of KSEA. Generally south to
southwesterly winds.

KSEA...MVFR cigs through the morning, with gradual improvement to
VFR this afternoon (likely between 19-21z). A few showers will be
possible later this afternoon into this evening. VFR cigs later this
afternoon will likely drop to MVFR tonight. Winds south-
southwesterly. JD
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&&

.MARINE...
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Generally south to southwesterly winds for the interior
waters today with northwesterly winds continuing for the Coastal
Waters. Small Craft Advisory winds and seas for the Coastal Waters
will continue through tonight. Winds will subside further Sunday
morning through Sunday night. Another weather system will slide
south across the offshore waters on Monday, with increasing offshore
winds Monday and Tuesday. Additional headlines are likely during
this period, especially for the Coastal Waters and the Strait of
Juan de Fuca with increasing easterly winds. Seas of 11 to 14 feet
today will slowly subside to 6 to 8 feet on Sunday. JD
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&&

.HYDROLOGY...No river flooding the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None.
PZ...Small Craft Advisory until 4 AM PDT Sunday 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-Grays Harbor Bar.

     Small Craft Advisory until 5 PM PDT this afternoon for West
     Entrance U.S. Waters Strait Of Juan De Fuca.
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&&

$$