Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KSEW 261519
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
820 AM PDT Wed Jul 26 2017

.SYNOPSIS...Coastal marine layer low clouds spread into parts of
Western Washington this morning. The clouds will burn back toward
the coast today and temperatures will be a bit cooler. Marine layer
clouds are likely on Thursday, and then Friday and Saturday will
probably have fewer morning low clouds. Sunday and Monday might see
deeper marine air--but no significant weather systems will affect
the area and dry weather will continue.


&&

.SHORT TERM...Marine layer stratus and fog patches are in portions
of the lowlands this morning. Onshore flow today and tonight will
set up Western Washington for deeper marine layer clouds that will
burn off later on Thursday and the coast might not break out much.
Temps will be cool on the coast, and there will be cooler temps
for the interior of Western Washington through Thursday. Friday
and Saturday should see max temps inch up again in time for the
weekend and marine layer clouds should be shallow and mainly
confined to the coast.

.LONG TERM...The GFS yesterday showed 500mb heights rising to
around 590dm over Western Washington over the weekend but the ECMWF
was not as warm. Looking at the 00z ECMWF shows the upper heights
falling off to around 585dm with the upper ridge axis far off to the
east over Montana. An upper trough just offshore will help generate
marine layer clouds at times--so the weather is likely to be more
of the same. The UW wrfgfs 0-3kft cloud mixing ratio forecast also
does not go crazy and suggests not much change in the current
pattern.
It shows the more morning low clouds on Sunday and less of that on
Monday.

&&

.AVIATION...Southwest flow aloft will prevail today and tonight
with an upper trough offshore. At the surface, onshore flow will
continue with high pressure offshore and lower pressure inland. The
air mass is stable.

Areas of low clouds and fog will mostly burn off later today. Low
clouds will redevelop and spread back inland tonight. Stratus
coverage Thursday morning should be more widespread and slower to
burn off during the day.

KSEA...Low cloud patches nearby could give a ceiling off and on
for the next two or three hours. Clear after that. Low clouds
will reach the terminal Thursday morning and then burn off in the
afternoon. Light wind will become west 4-8 knots today. Schneider

&&

.MARINE...Onshore flow will continue for the next several days
with high pressure offshore and lower pressure inland. Gale
force west winds are expected over the Central and Eastern Strait
of Juan De Fuca today. Small craft advisory strength west winds
are likely each night in the Strait for the rest of the week.
Schneider

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Warning until 5 AM PDT Thursday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory from 5 PM this afternoon to 5 AM PDT
     Thursday for Admiralty Inlet-Northern Inland Waters
     Including The San Juan Islands.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/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.