Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 242214
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
314 PM PDT Mon Apr 24 2017

.SYNOPSIS...A low pressure system over the area will continue moving
east and will be followed by high pressure aloft. Another low
pressure system will bring more precipitation and locally breezy
conditions to the area Tuesday afternoon and night. Showery, post-
frontal, weather will prevail on Wednesday. Unsettled weather will
continue on Thursday.

&&

.SHORT TERM...
There were some showers over mainly the southern part of the
forecast area at this time. This activity will gradually diminish
while shifting east during the next several hours. By late this
evening, the activity should be confined to the central Cascades.
Meanwhile, look for the low pressure system responsible for the
recent unsettled conditions to move over the Great Basin later
tonight. An upper level short wave ridge of high pressure will
follow in its wake.

It should be dry across much of the area Tuesday morning under high
pressure aloft. Precipitation associated with a cold or occluded
front is anticipated to move onto the coast early Tuesday afternoon,
overspreading the rest of the CWA by Tuesday evening. This front is
expected to sweep across the region late Tuesday night or Wednesday
morning for wet weather. Expect locally breezy conditions ahead of
and behind the front.

The upper level trough of low pressure will move across the region
during the day Wednesday for showery conditions. There is a
possibility that the Cascades (above 4000 feet) could receive
snowfall amounts meeting low end advisory amounts (4-8 inches),
especially on Mount Rainier and within a Puget Sound Convergence
Zone (PSCZ) that will likely develop in the wake of the front
Wednesday.

Weak disturbances in the flow aloft will serve to keep a threat of
showers going in the forecast for Wednesday night and Thursday.

Temperatures will be below normal during this period.

.LONG TERM...
An upper level ridge will begin building over the Pacific Northwest
on Friday, leading to dry weather on Saturday. However, temps
anticipated to remain below normal due to increased cloud cover
during the day ahead of the next low pressure system.

Beyond Saturday, confidence in the forecast was low. The medium
range solutions differed on the timing of the synoptic scale
features. Therefore, chose to compromise between the various
solutions for Sunday and Monday. In other words, expect a
continuation of below normal temperatures and above normal
precipitation.

&&

.AVIATION...A low pressure system is moving inland and stronger
onshore flow may touch off a few showers this evening. Areas of low
clouds will form later tonight through Tuesday morning, those clouds
will lift ahead of the next front. That front will spread rain into
Western Washington by Tuesday evening.

KSEA...mainly scattered clouds this evening and then some areas of
low clouds are a pretty good bet later tonight and Tuesday morning.
The north breeze will turn southerly overnight.

&&

.MARINE...A surface low is moving inland and a northwest wind is
picking up over part of the coastal waters this afternoon. The
westerlies in the Strait should get going later this afternoon
through evening. A front will arrive Tuesday afternoon and evening.
Strong onshore flow Wednesday will gradually ease through the end of
the week as high pressure builds.

&&

.CLIMATE...
So far, there has been 44.66 inches of rain at Seattle-Tacoma
International Airport since October 1st, 2016. This breaks the
previous October through April record of 44.52 inches set in the
2015-16 water year.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 10 PM PDT 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-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 3 AM PDT Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

An illustrated version of this forecast discussion can be seen at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html



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