Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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869
FXUS66 KSEW 221711
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
911 AM PST Sun Jan 22 2017

.SYNOPSIS...A band of showers rotating around a deep low over the
offshore waters will move north through the area today. Showers
will taper off from the north tonight as the offshore low drops
southward into California. High pressure aloft will result in
mainly dry conditions Monday through Wednesday and possibly
through the remainder of next week as well.

&&

.SHORT TERM...A deep and mature 970 mb low is centered near 46N
130W this morning. The low has a well defined bent-back occlusion
wrapping around its south side, and cold air well to the south of
the low. Thunderstorm activity this morning is limited to where
the coldest convective cloud tops are seen off the central and
southern Oregon coast.

For today, the forecast area will see a band of light rain
associated with an occluded front lift north from the Central
Puget Sound area northward to the Canadian border early this
afternoon. This will be followed by some shower activity that is
wrapping around the offshore low. Offshore pressure gradients are
peaking at this time as the occlusion moves northward across the
region, so breezy conditions in the East Puget Sound Lowlands and
near the west entrance to Snoqualmie Pass will die down around
noon. Temperatures spiked a bit in the Seattle area early this
morning as the offshore pressure gradients increased. Temperatures
will likely remain steady for the remainder of the day. The 12Z
NAM and GFS solutions show another organized band wrapping around
the low this evening through early Monday morning, but this band
never moves onshore as the entire vertically stacked low starts
shifting southward through the offshore waters of Oregon on
Monday.

Monday will be mostly cloudy across the area but dry. The GFS
shows a couple of light showers at the northeastern-most Olympic
Mountains and around Mount Rainier, but is otherwise dry. The NAM
and ECWMF show plenty of cloud cover but dry conditions on
Monday. An upper level ridge with light low level flow will result
in partly cloudy and dry conditions Monday night and Tuesday.

A first period update to the zones and grids was issued to
account for the warmer morning temperatures, the breezy conditions
near the Cascades and entrances to the passes, and to refine the
timing and qpf with the occlusion now lifting north across
Western Washington. Otherwise the forecasts are in good shape this
morning. Albrecht

.LONG TERM...From the previous long term discussion: A weak
weather system could bring spotty light rain later Wednesday into
Thursday. It`s hard to believe this will amount to much as it will
be moving into a sharp upper ridge but a small chance of showers
cannot be ruled out. High pressure aloft will remain in control
Friday and Saturday with dry weather expected. Schneider

&&

.AVIATION...An occluded front will lift north through Western WA
this morning with light rain across the area. The flow aloft is
southerly. Surface flow is E/SE and ceilings are mainly VFR.
Showers will diminish this evening as the front pushes farther
north into B.C. 33

KSEA...E/SE winds, VFR, with light rain in the area this morning.
Winds backing to NE after 06z tonight. 33


&&

.MARINE...A 965-970 mb surface low will track along 130W today
with an occluded front moving inland this morning. This front may
produce gale force winds over the Coastal Waters and a Gale
Warning is in effect. Winds will ease tonight. The flow over
Western WA will turn northerly on Monday as the surface low
weakens then drifts south offshore. High pressure will bring
generally light winds to the area Tuesday through Thursday. 33

&&

.HYDROLOGY...River flooding is not expected for the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Warning until 6 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.

     Small Craft Advisory for rough bar until 6 PM PST Monday for
     Grays Harbor Bar.

     Small Craft Advisory until 6 PM PST this evening for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca-Northern Inland Waters
     Including The San Juan Islands-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$

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You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html



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