Heavy Snow and Winter Weather in Washington, March 2 to 3, 2023

Area Forecast Discussion
National Weather Service Seattle WA
340 PM PST Thu Mar 2 2023

.SYNOPSIS...Another period of active weather will begin today
through Friday as a frontal system brings periods of mountain snow
and lowland rain. A cool troughing pattern over the Pac NW during
this period will also keep the potential of lowland snow alive.
Cooler and showery conditions through the weekend with lower snow
levels through the late night and morning hours.

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.SHORT TERM /TONIGHT THROUGH SUNDAY/...Showery precip continues to
move eastward in the wake of the front this morning. Given the
nature of these showers, there are hints at some instability,
however it does not seem to be enough to trigger any thunder
concerns as latest obs show nothing in the way of strikes. This risk
will still remain over the northern half of the Cascade foothills
for the remainder of the afternoon before conditions start to
stabilize this evening. Speaking of the Cascades, current /312 PM
PST/ radar shows two convergence zone style echoes, one over central
Skagit County and the other over northern King County...each likely
producing a fair amount of snowfall for the adjacent
Cascades...while the Southern Cascades continues to see persistent
waves of showers, but nothing that lingers too long. That said,
inherited headlines look good to continue unaltered for the
afternoon forecast package.

Showery precip is expected to persist throughout the day Friday as
an upper level low descends southward into the area. The center of
this low will move more over the coastal waters and as such, most
instability and resultant slight chance for thunder will reside
there. As snowfall tapers off throughout the day for the Cascades
Friday, snow activity over the Southern Olympic Mountains will ramp
up throughout the day. Expected amounts with the current forecast
would suggest that a headline may be needed there, however, will
punt that decision to following shifts as confidence in this
occuring is anything but confident. Saturday sees the upper low
continue its gradual southward trek as the feature continues to
cycle moisture into the area...keeping PoPs likely to categorical
throughout the morning and afternoon. Forecast dilemma for the
lowlands for both tonight into Friday morning as well as Friday
night into Saturday morning will be the risk of snow...as overnight
lows do dip right around or just below freezing and snow levels get
down to around 400-600 ft. Given the borderline nature of temps,
cannot imagine much in the way of accumulation should snow occur
with the more likely outcome being a rain/snow mix. Any light
accumulations that do occur will be limited to grassy areas or
elevated locations such as bridges and overpasses.

The upper low finally moves away enough to allow for some drying
Saturday night into Sunday, although PoPs do not go away completely.
Still, PoPs Sunday are expected to range generally from 20-40 pct,
definitely a change from the previous two days.

Daytime highs in the short term will see a bit of warming, highs
Friday generally in the lower to mid 40s while widespread mid 40s
are expected both Saturday and Sunday.  18

.LONG TERM /MONDAY THROUGH THURSDAY/...While deterministic models in
the long term have more of a wet picture to them, ensembles do not
seem terribly impressed. Much like the final day of the short term,
PoPs do not entirely disappear from the forecast, but they remain
low...locked solidly in slight chance to low-end chance for the
majority of next week. Continuing the trend from the short term,
overnight lows will hover right around freezing, typically ranging
from the high 20s to the lower 30s...and as such, any precip during
the overnight hours may be either a rain/snow mix or light snow.
Daytime highs throughout the long term will warm a little bit more,
with temps in the mid to upper 40s, perhaps breaking 50 in some
spots...hinting that spring may be trying to work its way into the
PacNW.  18

&&

.AVIATION...Westerly flow aloft through tonight. Generally VFR this
afternoon with isolated convective showers across Western
Washington. Cigs may briefly lower this afternoon/evening to MVFR in
heavier showers, with the best potential in an ongoing convergence
zone across portions of northern King/Snohomish County. Isolated
thunder and small hail are also possible, mainly in the convergence
zone into this evening. VFR into tonight with cigs lowering
potentially to MVFR into Friday morning. In addition, rain may
transition to rain/snow showers late tonight into Friday morning in
heavier showers, however little to no snow accumulation is expected
for most sites. Breezy W/SW winds continues into tonight, easing
briefly Friday morning before increasing again Friday afternoon.

KSEA...VFR cigs this afternoon into this evening with generally mid-
level clouds around. Convergence zone activity is expected to remain
north of the terminal. Isolated showers are expected into Friday
morning, with the slight potential of a rain/snow mix, particularly
Friday morning, however no accumulation is expected. Winds will
continue to be breezy W/SW into Friday. JD

&&

.MARINE...Onshore flow continues this afternoon into tonight with
the post-frontal airmass. Gales for the central and eastern Strait
of Juan de Fuca will continue this evening before tapering off
tonight. Small Craft Advisory winds for the Puget Sound with
increased south/southwest winds through the majority of tonight as
well. SCA winds will continue for the coast into Friday morning
before briefly subsiding. Another weather system will linger
offshore Friday night into the weekend for another round of
increased winds. Small Craft Advisory south/southeasterly winds
during this period, with a slight chance for gales along portions of
the Strait of Juan de Fuca. Winds will become lighter early next
week.

Combined seas building 15 to 18 feet tonight into Friday before
gradually subsiding through the weekend, though seas are expected to
generally remain over 10 feet through at least Sunday before
dropping below 10 feet into early Monday. JD

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

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.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until 10 AM PST Friday for West Slopes
     North Cascades and Passes.

     Winter Storm Warning until 4 AM PST Friday for West Slopes North
     Central Cascades and Passes.

     Winter Weather Advisory until 10 PM PST this evening for West
     Slopes South Central Cascades and Passes.

PZ...Small Craft Advisory until 4 PM PST Friday 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-West Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning until 10 PM PST 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 from 10 PM this evening to 7 AM PST Friday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 10 PM PST this evening for Admiralty
     Inlet-Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 4 AM PST Friday for Puget Sound and
     Hood Canal.

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