Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 261713
Area Forecast Discussion
National Weather Service Seattle WA
913 AM PST Sun Feb 26 2017
.SYNOPSIS...An upper trough off the Washington coast will move
south into northwestern Oregon this evening. Another upper
trough will move across Washington Monday afternoon through
Tuesday morning. Rain and snow showers are likely. A series of
systems will move through the area Wednesday through the rest of
the week, with snow levels over 2000 feet from Wednesday onward.
.SHORT TERM...A cool upper level low off Hoquiam continues to
spawn showers in western Washington this morning. The snow level
turned out to be More like 600-800 feet around central Puget
Sound, so most of the metro area did not get snow. An inch or two
fell above that level, and also lower down in northern areas and
near Hood Canal. The winter weather advisory for the lowlands will
be allowed to expire at 10 AM this morning. Rain showers will
taper this afternoon. Highs today will be in the low to mid 40s.
The mountains received 4 to 8 inches of snow overnight and will
get another 4 to 8 inches through this evening. A winter weather
advisory is in effect for all of the mountains except for the
Cascades of Whatcom and Skagit counties - where snowfall amounts
An upper trough will move through the region Monday, spawning more
showers. Most of the showers will be in the mountains and in a
possible convergence zone. Temperatures Monday will be cold for
late February with lows in the upper 20s to low 30s and highs in
the upper 30s to mid 40s. The showers could have snow at times,
but QPF will be noticeably lighter and no significant accumulation
is forecast in the lowlands.
Monday night and Tuesday morning will be mostly dry, but an
impulse moving through northwest flow aloft will enhance showers
in the afternoon, especially on the coast and in the mountains.
Highs Tuesday will be in the low to mid 40s. Burke
.LONG TERM...Previous discussion...A third system will form off
Vancouver Island on Tuesday and will track across northern
portions of the area Tuesday night and Wednesday morning. This
third system will have more onshore flow, and as a result will
have higher snow levels, around 2000 feet.
A series of systems will move through the area Wednesday through
early next weekend. Snow levels will be rather low, 2000-3000
feet. The GFS shows stronger zonal flow than the ECMWF -which
results in the potential of large snowfall amounts in the Cascades
late in the week. Breezy to windy conditions will rule the
lowlands with temperatures mainly in the 40s. Albrecht
.AVIATION...A cold upper trough is over the region. Areas of
rain and snow with low cigs and poor vsby will give way to some
partial clearing later today as the low shifts slowly south.
The air mass is stable over the inland portion of Western WA
but radar shows a more convective air mass along the coast
closer to the upper low.
KSEA...Periods of wet snow or rain will fall this morning
and then cigs should lift in the afternoon with some partial
clearing later today. Pres gradients are turning NEly, so that will
help dry the air mass this afternoon after the precip tapers off.
.MARINE...A 1003 mb low was near the WA coast moving south this
morning. Winds will turn northeasterly as the low tracks south.
The UIL-BLI gradient was -3.8mb at daybreak, so a small craft
advisory was issued for the Strait of Juan de Fuca. An area of
low pressure should remain over the region into Monday.
A frontal system is forecast to move ashore Tuesday night
with stronger low level onshore flow. The next stronger frontal
system is due to arrive Thursday.
.HYDROLOGY...No flooding is expected during the next week.
WA...Winter Weather Advisory until 10 AM PST this morning for
Admiralty Inlet Area-Bellevue and Vicinity-Bremerton and
Vicinity-East Puget Sound Lowlands-Everett and Vicinity-
Hood Canal Area-San Juan County-Seattle and Vicinity-
Southwest Interior-Tacoma Area-Western Skagit County-
Western Whatcom County.
Winter Weather Advisory until 10 PM PST this evening for
Cascades of Pierce and Lewis Counties-Cascades of Snohomish
and King Counties-Olympics.
PZ...Small Craft Advisory until 5 AM PST Monday for Grays Harbor Bar.
Small Craft Advisory until 8 AM PST Monday for Coastal Waters
From Cape Flattery To James Island 10 To 60 Nm-Coastal
Waters From James Island To Point Grenville 10 To 60 Nm-
Coastal Waters From Point Grenville To Cape Shoalwater 10
To 60 Nm.
Small Craft Advisory until 2 PM PST this afternoon for Central
U.S. Waters Strait Of Juan De Fuca-Coastal Waters From Cape
Flattery To James Island Out 10 Nm-East Entrance U.S.
Waters Strait Of Juan De Fuca-West Entrance U.S. Waters
Strait Of Juan De Fuca.
You can see an illustrated version of this discussion at