Scientific Forecaster Discussion
Area forecast discussion...corrected
National Weather Service Seattle Washington
345 PM PDT Friday Jul 11 2014
Corrected typo in the synopsis.
Synopsis...high pressure aloft will remain over the region through
Monday for well above normal or possibly near record high
temperatures. An upper low off the California coast will bring a
relatively moist and unstable air mass to the area on Saturday. The
low will weaken and move across the area Sunday night.
an upper ridge will prevail over the region through Monday for
continued well above normal or possibly near record temperatures across
much of the County Warning Area. The excessive heat watch was upgraded to a heat
advisory for much of the Puget Sound sound region for this weekend.
A heat advisory was also issued for part of the southwest
interior. There is a chance that the advisory will need to be
extended through at least Monday.
This will be a fairly lengthy period of well above normal temperatures
for the interior especially. This combined with above normal
minimum temperatures...especially over parts of the Puget Sound sound...will
make it uncomfortable for some. For example...the normal min temperature
for Seattle is in the middle 50s. The forecast calls for the middle 60s
Sunday and Monday night.
Meanwhile...moisture and instability rotating around an upper low
offshore will bring a risk of thunderstorms to the interior...mainly the
mountains...on Saturday. The remnants of the upper low...in the
form of an open trough...will move across the area Sunday night...
resulting in a better chance of thunderstorms and over a larger part of
the County Warning Area.
the upper ridge will remain over the region through midweek for
continued above normal temperatures across much of the County Warning Area. The ridge
will weaken some or shift well east of the area...depending on
which model one prefers...during the latter part of the period.
The GFS was quite aggressive in developing an upper trough over the
Pacific northwest whereas the European model (ecmwf) kept an upper ridge over the
region. Chose to compromise between these two extremes. In other
words...the forecast showed temperatures cooling to near or slightly
Aviation...marine stratus and fog along the coast will push into
the Strait of Juan Delaware fuca and the Chehalis gap overnight...the
North Bend Oregon to Seattle gradient was 2mb at 2pm this afternoon
and will probably get a bit higher...so there is a good chance that
marine air and stratus will make it into Shelton and Olympia.
Otherwise...just some high clouds are expected to arrive from the
thunderstorms over Oregon this afternoon.
Ksea...clear skies and an afternoon and evening northerly breeze...then
some cirrus later tonight. The forecast is that the marine layer
will not make it to sea tac Saturday morning...but it will probably
spill into the south part of Puget Sound sound.
Marine...higher pressure is offshore with thermal lower pressure
inland. The disturbance that is over southern Oregon giving that area
some thunderstorms this afternoon is helping to induce a shallow
marine push...so the stratus and fog on the coast this afternoon
should push into the Strait tonight...but only a few areas of fog
and low clouds are likely to make it further inland that than.
Perhaps around Whidbey Island...and around Shelton/Olympia. The
pattern of afternoon and evening diurnal sea breeze winds should
continue through the weekend.
Washington...heat advisory in effect for much of the Puget Sound sound region
and southwest interior from 11 am Saturday until 6 am Monday.
For the graphical afd...visit