Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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536
FXUS66 KSEW 181621
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
921 AM PDT Sun Jun 18 2017

.SYNOPSIS....A weak warm front over the coastal waters will
continue lifting north today. Expect clearing from the south to
take place this afternoon. High pressure aloft will prevail
tonight and Monday. Look for a weak disturbance to bring cooler
temperatures and a few showers to the area on Tuesday.

&&

.SHORT TERM...
Per CoCoRaHS reports, most 24-hour rainfall amounts were in the
tenth to quarter inch range; however, on the coast amounts ranged
from a quarter to near a half inch. There were a few places that
did not receive measurable rainfall but these places seemed to be
the exception not the rule. Note: The observation page, on the
web site, is experiencing a technical problem that is being looked
into.

The tail end of the warm front was over the coastal waters at this
time, and appeared to be in the vicinity of buoy 46041, off Cape
Elizabeth. Expect the front to continue lifting north during the
day today, with clearing occurring from south to north. Visible
satellite imagery already showed some thinning of the clouds over
parts of Lewis County. There was also a small pocket of nearly
cloud-free skies over northeast Jefferson County due to shadowing
to the lee of the Olympic range.

A strong upper level ridge over the Southwest will keep heights
high over the Pac NW on Monday, near 580 dam. Guidance shows a
few spots in the interior reaching the lower 80s with mostly sunny
skies. The coast will be a little cooler with onshore flow - highs
near 70.

The ridge will flatten over W WA on Tuesday while a cold front
moves inland. This front will bring mainly isolated showers to the
area. But there is a chance a Puget Sound Convergence Zone may
form in the afternoon/evening as onshore flow increases. The
cooler marine air will knock temps down a few degrees - close to
normal. 33/05

.LONG TERM...
The stronger push will bring status clouds inland overnight for a
cloudy start to Wednesday. We may only see partial clearing in
the afternoon as onshore pressure gradients stay strong.

The weather pattern continues to look rather benign through the
long term period. Low level onshore flow will prevail through the
end of the week for areas of late night and morning clouds. We
should see stratus clouds burning back toward the coast during the
afternoon. A ridge will shift inland over the weekend for a
warming trend - interior temps back into the lower 80s. Onshore
flow will keep coastal temps in the mid 60s to lower 70s. 33

&&

.AVIATION...A frontal system will dissipate over Western
Washington today. Westerly flow aloft will prevail through
tonight. At the surface, weak high pressure over the area will
shift slightly north tonight with light northerly flow developing.
The air mass is moist and stable. Widespread low clouds will lift
and break up this afternoon and evening.

KSEA...IFR low clouds should lift to MVFR by midday, then lift to
VFR late this afternoon. Low clouds should scatter entirely this
evening. Southerly wind 4-8 knots will become northerly this
evening. Schneider

&&

.MARINE...Southerly winds will be below 20 knots today as a weak
front over the area dissipates. Onshore flow will develop on
Monday and continue through Thursday. The strongest onshore flow
looks like it will occur Tuesday and Wednesday. Gales are
possible in the Central and Eastern Strait Tuesday and Wednesday
evening. Schneider

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.

&&

$$

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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