Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
854 am PDT Sat Jul 30 2016
Synopsis...an upper level low pressure trough will track across
British Columbia today through Sunday morning, brushing western
Washington and increasing our cooling onshore flow. A closed upper
low will move across northwest Washington on Monday night and
Tuesday morning, bringing scattered showers and lower
temperatures. Sunny skies and higher temperatures will return by
the middle of next week.
Short term...a weak upper level trough and onshore flow will
bring cooler conditions to western Washington today. Temperatures
will be 10-15 degrees cooler in the interior with highs mainly in
the 70s. The coast will see highs in the mid 60s, close to normal.
Stratus clouds will likely break up this afternoon for partly to
mostly sunny skies.
An upper level low will continue to spin over b.C./Alberta on
Sunday with a weak trough over western Washington. Models are indicating
a stronger onshore push and low cloud cover will be more extensive
Sunday morning. Temperatures will remain mild, close to what we
will see today.
On Monday, an upper level low will spin off the coast then move
inland during the evening. The air mass will be moist and unstable
with a chance of showers across the region. Isolated thunderstorms
may develop over the north Cascades and possibly the Olympics. 33
Long term...the upper low will exit into eastern Washington on
Tuesday afternoon, leading to diminishing shower chances late
Tuesday. However, the clouds, lingering showers and strong onshore
flow will make Tuesday the coolest of the next 7 days. Upper
heights will rise on Tuesday night and Wednesday, with rain-free
weather and a warming trend on Wednesday. For Thursday and Friday,
moderate onshore flow with 575-580 dam heights at 500 mb, as well
as rain-free weather will to classically normal early August
weather in the Pacific northwest. Haner
Aviation...an upper trough over the Pacific northwest will bring
westerly flow aloft today and tonight. At the surface, onshore
flow will prevail with high pressure offshore and lower pressure
inland. The air mass is stable.
Low clouds continue to linger over a fair amount of western
Washington this morning...resulting in MVFR conditions for the
southern two-thirds of the area. Whatcom and Skagit counties are
generally clear along with some clear spots along the coast. Still
expecting clouds to burn off as the morning progresses...with mostly
clear skies and a return to VFR conditions by afternoon. So as not
to break the pattern...this cloud cover is expected to re-emerge
late tonight and into Sunday morning.
Ksea...cigs bkn010-015 this morning before becoming mostly clear
today. Low clouds are expected to return tonight after midnight.
Southerly wind 5-10 knots. Schneider/smr
Marine...onshore flow will prevail for the next several days with
high pressure offshore and lower pressure. Small Craft Advisory
westerly winds are likely most evenings in the central and
eastern Strait of Juan de Fuca.
For the outer coastal waters, there will be some borderline gale
force northwest winds this morning. Otherwise, there will be Small
Craft Advisory northwest winds for the next couple of days with
winds gradually easing overall. Will hold off on issuing follow up
Small Craft Advisory until the afternoon forecast package.
There will also be some 10-13 foot short period northwest swell
over the outer coastal waters this weekend. This will subside to
more normal summertime levels early next week. Schneider/smr
Pz...Small Craft Advisory until 5 am PDT Sunday 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 10 to 60 nm-
coastal waters from Point Grenville to Cape Shoalwater out
Gale Warning until 6 PM PDT this evening 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.
Small Craft Advisory from noon today to 5 am PDT Sunday 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 3 am PDT Sunday
for Admiralty Inlet-northern inland waters including the
San Juan Islands.
Small Craft Advisory from noon today to 3 am PDT Sunday for West
Entrance U.S. Waters Strait of Juan de Fuca.
You can see an illustrated version of this discussion at