Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 182348
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
430 PM PDT Tue Jun 18 2019

.SYNOPSIS...A weak upper level trough will pass mainly north of
the area tonight followed by a deeper trough that will shift
southward across the area Wednesday night into Thursday. This will
produce a chance of showers across the area...especially in the
mountains Wednesday night and early Thursday. Weak high pressure
will build into the region Friday and early Saturday before another
trough settles over the region early next week.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Leftover cloud from
earlier convergence zone continues across much of the Puget Sound
area late this afternoon while much of the coast and north interior
enjoys some clearing. Expecting cloud cover to fill in across
Western Washington overnight as a trough approaches the region. May
see some light precip develop up near the Canadian border by just
after daybreak Wednesday with a better chance for showers spreading
southward as the day goes on. Models develop a convergence zone over
the central Puget Sound Wednesday evening then shift it into the
Cascades overnight. Most of the shower activity should be in the
mountains by Thursday morning as the trough axis exits the area.
Weak upper level ridging builds into the region Thursday night into
Friday..giving the area a break in the weather and a brief return to
near normal temperatures before another trough arrives for the
weekend.

.LONG TERM /SATURDAY THROUGH TUESDAY/...

Previously mentioned upper ridging lingers into Saturday but
flattens quickly as another upper trough digs southward down the
British Columbia coast toward the region. The GFS and Euro diverge
with the trough`s path by early next week...so this certainly comes
into play with timing and placement of precip. However...the
longwave trough position looks to be parked over the West Coast
nearly all of next week. Above average precipitation and below
normal temperatures are a safe bet as we head into Monday and
beyond.   27

&&

.AVIATION...Westerly flow aloft through Wednesday with a weak
system moving by to the north tonight. In the lower levels onshore
flow continuing into Wednesday.

Areas of low MVFR continuing to linger around primarily Puget
Sound will slowly improve through this evening before
deteriorating again late tonight ahead of an approaching upper
trough. May see some light rain develop across the north interior by
mid morning Wednesday.

KSEA...MVFR ceilings continue with some slow improvement to the
low end of VFR possible after 00z. Ceilings lowering back down to
1000-1500 feet overnight. Surface winds southwesterly less than 10
knots backing to southerly by early Wednesday and increasing to 10
to 15 knots. 27

&&

.MARINE...High pressure over the coastal waters with lower
pressure inland will result in varying degrees of onshore flow
through the week. Gale force westerlies continue in the central and
easternStrait of Juan de Fuca this evening into the early morning
hourson Wednesday with small craft advisory winds in Admiralty
Inlet. Small craft winds also expected over coastal waters through
much of Wednesday. Onshore flow continuing through the week with
small craft advisory winds in the central and eastern Strait each
evening Wednesday through Saturday. 27

&&

.HYDROLOGY...While big precipitation producing storms occurred last
fall and early winter, it has been much drier than normal since the
start of 2019. The warmer, dryer spring has left the area with
growing water supply issues. The snow pack was lower than normal in
May and has since mostly melted out already. Most western Washington
rivers are running below normal with a handful having daily record
low flows. And for much of western Washington, the water supply
forecasts are for below normal volumes, many in the 5 percentile
range of lower. Please see our Drought Information Statement, Water
Supply Outlook, and Drought Information webpage at:

https://www.wrh.noaa.gov/sew/hydro/droughtsew-A1.php.
jbb

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 PM PDT Wednesday 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.

     Gale Warning until 2 AM PDT Wednesday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until 2 AM PDT Wednesday for Admiralty
     Inlet.

&&

$$

www.weather.gov/seattle



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