Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 192253
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
353 PM PDT Sun Mar 19 2017

.SYNOPSIS...High pressure and drying low-level offshore flow will
continue through Monday morning. Then southerly flow aloft will
increase and open the door to wet weather systems coming up from
the south starting late Monday or Monday night. A cold front on
Wednesday morning will enhance rainfall. A brief dry lull is
possible on Thursday, then a return to wetter southerly flow is
expected again starting Thursday night or Friday.

&&

.SHORT TERM...An upper level high pressure ridge will move across
Western Washington this evening, and drying low-level offshore
flow will develop and strengthen. Other than some high clouds,
this will keep the weather mostly clear and rain-free into Monday
morning.

After the upper ridge axis exits to our east late tonight, flow
aloft will back from westerly to southwesterly on Monday. The flow
will then become southerly on Monday night and strengthen on
Tuesday. On Monday PM, this will bring up plenty of mid-high level
moisture. Falling upper heights and shortwave energy coming up
from the south will eventually help precip spread up from the
south. Will take awhile for the rain from our south to overcome
the drying low-level easterly flow, but more organized precip
spreading up from the south on Monday night will eventually
overcome the dry low-level air. Even so, rain will be on the
lighter side. Snow levels will be up around 5000-5500 feet.

Following Monday night`s round of rain, may be some dry breaks on
Tuesday, but some disorganized dribs and drabs of rain will
continue in the moist southerly flow aloft. Precip will blossom
again on Tue night and peak on Wed morning prior to the passage of
an eastward-moving cold front. Showers will continue behind the
front on Wed PM.  Haner

.LONG TERM...An upper ridge should briefly pump up over the area
on Thursday, bringing the best chance of a 12-24 hour period of
dry weather from Monday night through the rest of the week. The
upper ridge will quickly pass east late Thursday, with
strengthening S-SW flow aloft following right on its heels. A
shortwave will ride up in southerly flow on Friday, with the
another good shot of rain at that time. Looks like Friday`s
system will start to split just as it reaches the U.S. west coast,
so mainly moderate precip amounts expected over Western Washington.
An upper trough axis will pass by next Saturday, with the cooler
air aloft and onshore flow supporting showers. Models show an
upper ridge briefly appearing next Sunday before another turn to
wetter SW flow aloft occurs. Haner

&&

.AVIATION...A weak upper ridge will move east across the area
tonight giving westerly flow aloft. Flow aloft will turn southerly
on Monday as the upper ridge moves east and a trough develops west
of the area. At the surface, high pressure over the area will
shift north and east of the area giving low level northeasterly
flow. The air mass is dry and stable. High level moisture will
thicken and increase from the south Monday afternoon.

Expect good VFR conditions through Monday. Patchy fog will form in
more fog-prone river valleys of the south interior late tonight
and Monday morning, but it will tend to be shallow due to an
increase in high level clouds during the typically good fog
formation time of day. Albrecht

KSEA...Scattered to broken thin cirrus through late tonight. High
level moisture will increase Monday morning and light rain falling
out of a OVC050 deck will begin late Monday afternoon. North wind
will increase to 10-15 kt this evening and continue through
Monday morning before turning more northeasterly and decreasing
midday. Albrecht

&&

.MARINE...North to northeast offshore flow will become moderate
tonight into Monday morning as surface high pressure moves from
northwestern Washington northeastward. Small craft advisories are
in effect for tonight into Monday for the coastal zones, the
western 2/3 of the Strait of Juan de Fuca, and Puget Sound and
Hood Canal starting this evening.

A series of difficult to time troughs will move northeastward
across the waters, roughly one every 24 hours, starting Monday
night and continuing through Friday. The strongest troughs are
most likely to move across the waters late Tuesday night or
Wednesday morning and on Friday. Each trough may give small craft
advisory conditions to mainly the coastal waters and portions of
the Strait of Juan de Fuca. Albrecht

&&

.HYDROLOGY...All area rivers are falling right now. River falls
will level off on Tuesday as a pattern with light-moderate rain
sets in for much of the rest of the week.

The White River at R Street is currently in the process of falling
through its defined flood flow. After it is confidently below
flood flow, no additional river flooding is expected in the next
7 days. The Skokomish will rise a bit on Wednesday following a
period of heavier rain on Wednesday AM.

Despite dry weather today, the landslide threat remains elevated.
USGS landslide thresholds are still in exceedance due to the
hangover effect from heavy rain over the past 2 weeks. Haner

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 6 PM PDT Monday 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 Point Grenville To Cape Shoalwater 10
     To 60 Nm-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until noon PDT Monday for Central U.S.
     Waters Strait Of Juan De Fuca-Coastal Waters From James
     Island To Point Grenville Out 10 Nm-Coastal Waters From
     Point Grenville To Cape Shoalwater Out 10 Nm-Puget Sound
     and Hood Canal.

&&

$$

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