Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

000
FXUS66 KSEW 210406
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
905 PM PDT Mon Mar 20 2017

.SYNOPSIS...A series of upper level disturbances will move
through the area tonight through Friday bringing clouds, rain and
locally breezy to windy conditions. Best chances for precipitation
are expected Wednesday and Friday mornings, with a break in the wet
weather possible on Thursday. Showers will diminish next weekend as
the upper level flow becomes westerly.

&&

.SHORT TERM...Northward moving blob of moisture will have some
difficulty in producing showers over the area as it struggles to hold
together. Current radar ends up looking more impressive than what
ground truth bears out. While plenty of echo returns over much of W
WA this evening...looking at obs it is clear that precip is meeting
with a fair amount of difficulty getting to most locations east of
Puget Sound...BLI seeming to be the only exception at the time of
this writing.

Thanks to either bad luck or worse scheduling...seems like
discussions by this forecaster always manage to come during the
rainy weeks...and this does not look to be an exception. Although to
be fair...W WA has had more than its fair share of rainy weeks so
far this year. Focusing on March in particular...all climate sites
in the area are already above normal when it comes to monthly
precip.  Will provide numbers in Climo section below for those
curious. Turning attention to the week ahead...precip activity is
expected to remain in some degree of disarray tonight and into
Tuesday...although it looks like things do kind of coalesce mid
morning Tuesday for a brief period before scattering out once more
by Tuesday afternoon. Wednesday sees a front with better upper level
support move into the area and thus...precip looks better organized
resulting in likely to categorical POPs area-wide. Precip amounts
will be on the generally light side...although some locations could
see some moderate amounts...but nothing that will result in any
precip-based river flooding. For further details on that...please
refer to Hydro section below.

To focus on something positive...temperatures look to remain mild
both Tue and Wed...sitting 1 to 3 degrees above seasonal normals.
And thanks to all the cloud cover...overnight lows will remain in
the 40s for lowland locations.

All in all...inherited forecast seems to be handling conditions
well. No evening updates needed. SMR

.LONG TERM...From previous discussion...Global models through the
first part of the weekend are in fairly good agreement today.
Thursday appears to be the best chance for a dry period over the
upcoming week. Both the GFS and ECMWF bring a north-south oriented
front into the offshore waters that will likely wait until late
Thursday night or Friday to move inland. While Thursday appears dry,
there will likely be quite a bit of mid and high clouds spreading
inland.

Friday will be wet as the front moves inland and possibly windy in
the afternoon as flow aloft behind the front interacts with the
terrain.

From later Saturday into early next week the forecast is more in
question. The operational GFS supports systems splitting into
southern Oregon and California while the ECMWF and majority of
GEFS solutions brings another system that looks like the Thursday
night and Friday system into the area later Sunday into Monday. A
blend that leans toward the preferred ECMWF was used as firsts
guess fields to populate the gridded forecasts. Albrecht

&&

.AVIATION...Southerly flow aloft over Western Washington this
evening will continue tonight and Tuesday, as a weak weather system
moves rather slowly through the region. At the surface, moderate to
strong northeasterly gradients will become more easterly tonight,
then more southeasterly Tuesday. The air mass will remain stable
with increasing mid and high moisture.

Conditions are low-end VFR for the most part at 8 pm with ceilings
040-060 and areas of light rain, except at the coast where ceilings
are 030-040. There should be little change tonight and Tuesday
morning, then ceilings should fall to MVFR 020-030 late Tuesday
morning or midday.

KSEA...Northeast wind 7-12 kt tonight, then southeast 5-10 kt
Tuesday. McDonnal

&&

.MARINE...Northerly and offshore flow will produce small craft
advisory north and east winds at times over all waters tonight.
Winds will turn more southeasterly late tonight as as weak frontal
system arrives from the south. Additional frontal systems - around
Tuesday night and Thursday night - will affect the waters later in
the week for off and on small craft advisory winds this week. Gale
force winds are possible on the coast Thursday. McDonnal

&&

.HYDROLOGY...From previous discussion...Increased releases from the
Mud Mountain Dam on the White River are expected to push the White
River at R Street near Auburn to just above flood stage late this
afternoon through tonight. A flood warning was reissued for this
point as a result. Any flooding is expected to be quite minor.
Elsewhere, river flooding is not expected for the next 7 days.

The ground is saturated due to the heavy rainfall of the past 2
months. Some shallow landslides continue to be observed today.
Rain at times over the next few days will keep the threat for
shallow landslides elevated across the area for the next few days,
and the special weather statement that is out for the landslide
threat will be continued. Albrecht

&&

.CLIMATE...All climate stations for W WA have exceeded their normal
monthly precipitation for March...and there is more precip on the
way for much of this week. Stations...their normal monthly amounts
for March and the precip they have received so far for March 2017
are as follows:

Sea-Tac -- Normal: 3.72 inches -- March 2017 so far: 5.38 inches
Olympia -- Normal: 5.29 inches -- March 2017 so far: 8.17 inches
Hoquiam -- Normal: 6.99 inches -- March 2017 so far: 11.25 inches
Quillayute -- Normal: 10.83 inches -- March 2017 so far: 12.85 inches
Bellingham -- Normal: 3.22 inches -- March 2017 so far: 3.82 inches

The combined rainfall for Sea-Tac for Feb and March so far should
provide some indicator as to why so many people have just about had
it with the rain...coming in at 14.23 inches. To give some
historical context...the record for combined precip over this period
is 15.55 inches set in 2014. Do not want to comment at this time as
to whether or not Sea-Tac will push for that record...as March is
two-thirds over...but on the other hand...it has been that kind of
year.  SMR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 PM PDT Tuesday 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-East Entrance U.S. Waters Strait Of
     Juan De Fuca-Northern Inland Waters Including The San Juan
     Islands.

     Small Craft Advisory until 11 AM PDT Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 11 PM PDT this evening for Puget
     Sound and Hood Canal.

&&

$$

www.weather.gov/seattle

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



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.