Scientific Forecaster Discussion
fxus66 ksew 200351
Area forecast discussion
National Weather Service Seattle Washington
900 PM PDT Wed Jun 19 2019
Synopsis...an upper trough will move south over western Washington
tonight into Thursday bringing showers. Weak high pressure will
build Friday and Saturday. Another trough will approach the area
late Saturday into Sunday and settle over the region early next week.
Short term /tonight through Friday/...no changes to the forecast
this evening. Puget Sound convergence zone formed over Snohomish
County and moved into north King County. There is also a band of
rain over western Whatcom and Skagit counties. Overall, shower
activity will become more widespread through the night across the
interior and Cascades. The coast will only get spotty showers at
best with this system.
Showers will be dissipating on Thursday and should be confined to
the Cascades by afternoon. Weak high pressure aloft begins nosing
into the region on Friday with temperatures returning to something
that resembles normal for the time of year. Chb
Long term /Saturday through Tuesday/...dry conditions will continue
for the majority of Saturday but upper ridging flattens quickly as
next upper trough shifts southward along the British Columbia coast.
The 12z runs of the GFS and Euro are in remarkably good agreement
with the path of the upper low through the middle of next week. By
later Tuesday, the trough looks to be parked just offshore of the
or/Washington border and doesn't move much as a series of disturbances
rotate into the region producing periods of showery weather and
keeping temperatures below normal much of the time. 27
Aviation...an upper trough will move into the area from the
northwest tonight. An upper low will remain inland on Thursday.
West to northwest flow aloft will become northerly later tonight
and Thursday. At the surface, onshore flow will continue with high
pressure offshore and lower pressure inland. The air mass is moist
and relatively stable.
5000-8000 foot ceilings this afternoon and evening will lower
1000-2000 feet later tonight. A Puget Sound convergence zone is
currently over mainly north King County. It is forecast to move
south tonight and dissipate. Local ceilings below 1000 feet are
possible in the pscz.
Ksea...pscz currently just north of the terminal. It will probably
reach the area then dissipate, with a few hours of northerly wind
resulting. Otherwise southerly wind 8-12 kt. Chb
Marine...onshore flow will continue through early next week with
high pressure offshore and lower pressure inland. At least Small
Craft Advisory strength west winds are likely most days in the
Strait. Gales are occurring in the Strait tonight and are possible
tomorrow night and again Saturday night. Have hoisted a gale watch
for Thursday afternoon and night as the only change to the marine
forecast. On the coast there will be Small Craft Advisory strength
northwest winds at times through at least Thursday. There will also
be Small Craft Advisory level steep west swell through Thursday. Chb
Hydrology...the daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
Pz...Small Craft Advisory until 5 am PDT Friday 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.
Small Craft Advisory until 11 PM PDT Thursday for coastal waters
from Cape Flattery to James Island out 10 nm-coastal waters
from James Island to Point Grenville out 10 nm-coastal
waters from Point Grenville to Cape Shoalwater out 10 nm.
Gale watch from Thursday afternoon through late Thursday night
for central U.S. Waters Strait of Juan de Fuca-East
Entrance U.S. Waters Strait of Juan de Fuca.
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 until 8 am PDT Thursday for Admiralty Inlet-
northern inland waters including the San Juan Islands.
Small Craft Advisory until 5 am PDT Thursday for West Entrance
U.S. Waters Strait of Juan de Fuca.
Small Craft Advisory until 2 am PDT Thursday for Puget Sound and