Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 261049
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
349 AM PDT Sun Mar 26 2017

.SYNOPSIS...Rain will spread inland this morning as a front
approaches western Washington. The front will move through the
area late this afternoon. Onshore flow and showers will follow the
front tonight and Monday. A warm front will move through Tuesday.
A rather wet frontal system will reach the area Tuesday night and
Wednesday. An upper trough and onshore flow will keep showers in
the forecast Thursday. A dry day with highs a little above normal
possible Friday as high pressure builds over the area.

&&

.SHORT TERM...And the beat goes on and on and on. Satellite
imagery shows the next frontal system to reach western Washington
offshore near 130w. Coastal doppler radar shows the rain out ahead
of the front starting to move onshore at 10z. Under cloudy skies
temperatures at 3 am/10z were in the 40s.

Offshore front will move through western Washington this later
this afternoon. Rain will spread inland this morning reaching the
Cascades by noon with rain continuing until the frontal passage.
Snow will add up quickly over the southern Cascades this
afternoon. Will put a snow advisory up mainly for new snow
accumulation at Paradise on Mount Rainier of 4 to 8 inches. Highs
in the lowlands will be well below normal...near 50 degrees.

Plenty of post frontal shower activity over the area tonight. Some
decent, not great, orographics behind the front with model 850 mb
winds up to 30 knots. Will go with a low end snow advisory for the
northern Cascades mainly for the snow accumulations on Mount
Baker and continue the snow advisory for the southern Cascades
with another 4 to 8 inches expected. Lows will be near 40.

Upper level trough moving through western Washington Monday
morning keeping showers in the forecast. The trough will be east
of the area in the afternoon with the shower activity mostly
confined to the mountains by late afternoon. High will continue to
be below normal, in the upper 40s to mid 50s.

Still could be some lingering showers Monday evening before a
very flat upper level ridge moves through the area. Increasing
cloud cover out ahead of an approaching warm front will keep lows
in the lower to mid 40s.

New model runs bringing the warm front on Tuesday further south
with rain expected over much of the area. Rainfall amounts will
not be very much with just a tenth to a quarter of an inch
possible in most locations. Highs once again will be in the upper
40s to mid 50s.

.LONG TERM...Extended models in good agreement with a very wet
system moving into western washington Tuesday night into
Wednesday for another round of rain. Upper level trough trailing
behind the front moving through late Wednesday night into Thursday
morning keeping showers in the forecast. A short dry spell
beginning Thursday night and continuing into Friday with an upper
level ridge building into the area. 500 mb heights rising up
into the lower 570 dms. Low level flow remains onshore so will
not go too crazy with the high temperatures. The warmer locations
could get into the lower 60s.

Model consistency breaks down on Saturday with the GFS keeping 500
mb heights in the low 570 dms which weakens the next system to
reach the area considerably. The ECMWF moves the ridge off to the
east with a stronger more consolidated system moving into the
area. With the model inconsistencies will just go for chance pops
on Saturday. Felton


&&

.AVIATION...The upper level ridge of high pres over the region will
move east during the day, allowing an upper level trof of low pres
and associated occluded front to approach the WA coast this
afternoon. The front will move onshore late today, and then sweep
across western WA this evening. Low level ely flow will become sly
this afternoon.

Meanwhile, areas of MVFR CIGs/VSBYs will dvlp this morning and
become more widespread by midday. Anticipate merging cloud layers
to 33K ft MSL. The mtns will be obscd.

KSEA...VFR conditions should prevail this morning. Anticipate MVFR
CIGs this afternoon, persisting thru tonight. Light ely winds will
become sly this evening with the passage of the occluded front.

&&

.MARINE...
An occluded front currently well offshore will move across the
coastal waters late today and the interior waters this evening.
Expect the easterly flow to become southwest behind the front. A
weaker occluded front will move across the coastal waters on Monday.
This may be followed by a stronger frontal system about midweek.

Meanwhile, long period (16 seconds) westerly swells of 12-14 feet
are forecast to arrive Tuesday night. The long period will make the
waves more powerful, leading to the potential for hazardous seas.

&&

.HYDROLOGY...River flooding is not expected for the next 7 days
with the exception of possibly the flood prone Skokomish river in
Mason County, where heavier rain in the Olympics Tuesday night
and Wednesday could be enough to get the river above flood stage
Wednesday. Felton

&&

.CLIMATE...It has been a wet March with all of the climate sites
in the forecast area headed for at minimum a top 10 wettest March
finish. There is a good chance all of the stations will end up
in the top 5 wettest for March. Below is a table with the
precipitation values through the 25th with the current rank, the
5th wettest value and the record for the month.

                   Current       5th wettest      Record

Seattle-Tacoma      6.12" (10th)    7.12"          9.44" (2014)
Olympia             9.37" (4th)                   11.79" (1997)
Bellingham          4.44" (12th)    5.07"          7.02" (1950)
Hoquiam            12.83" (8th)    13.25"         15.13" (1997)
Quillayute         15.76  (10th)   17.95"         23.23" (2007)

In Seattle since October 1st there has been measurable
precipitation on 121 days ( 69 percent ) out of the 176 days.
This is 2 more than the total from October 1st through March 31st
last year during the record setting rainfall. In over 120 years
of weather records the most days with measurable precipitation in
Seattle from October 1st through March 31st is 125 days set in
1950-51.

There was only 11 days with measurable precipitation in January in
Seattle. Taking that month out that makes 110 days out of 145 ( 76
percent ) for the other 5 months. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather advisory for the Cascades of Lewis and Pierce
     counties from noon today through early Monday morning.

     Winter weather advisory for the Cascades of Whatcom and Skagit
     county tonight

PZ...Gale Warning until 2 PM PDT this afternoon 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.

     Gale Warning until 5 PM PDT this afternoon for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm.

     Small Craft Advisory until 5 PM PDT this afternoon for Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Gale Warning until 3 PM PDT this afternoon for East Entrance
     U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters
     Including The San Juan Islands.

     Small Craft Advisory until 6 PM PDT this evening for West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until midnight PDT tonight for Admiralty
     Inlet-Central U.S. Waters Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
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