Scientific Forecaster Discussion
Area forecast discussion...corrected
National Weather Service Seattle Washington
1002 am PDT sun Jul 13 2014
Corrected typo in the last paragraph of the short term segment.
Synopsis...a low pressure system off the southern Oregon coast
will continue moving north today. This system will move across
the area late tonight. By Monday afternoon...it will be over
eastern Washington. The main impact this feature will have on
our weather will be to destabilize the air mass and strengthen
the onshore flow. High pressure aloft will prevail over the
region on Tuesday.
the radar mosaic showed showers and thunderstorms over northern Oregon
racing northward. Upper air soundings and the satellite derived
lifted index product indicated lifted indices near -1 degree
celsius over northern Oregon this morning. The thunderstorms were
occurring as far west as the Oregon near shore waters. Look for
this activity to move into the far southern part of the County Warning Area by
Meanwhile...the upper low off the far southern Oregon coast
will continue moving north during the day today. This system
will turn inland late this evening and then move across the
County Warning Area late tonight through Monday morning. Look for the thunderstorm threat
coverage to increase this evening as the upper low approaches.
The southeast half of the County Warning Area will have the best chance of
thunderstorms tonight. Expect the upper trough to move into eastern Washington
Monday afternoon. The threat of thunderstorms should become confined to
near the north Cascade crest by Monday afternoon.
An upper ridge will prevail over the region Tuesday.
Concerning temperatures...today will be another warm day across much of
the County Warning Area...especially the interior. Although...the southwest
interior might end up a few degrees cooler than yesterday due to
increased cloud cover and tightening of the onshore pressure
gradient. Temperatures will be a few degrees cooler on Monday due to onshore
flow and a cloudy start. Suspect that the NAM MOS guidance may be
too warm for Monday. Expect daytime temperatures to rebound on Tuesday.
Long term from the previous discussion...
long term models generally agreed on a return to more normal
temperatures as we move toward Thursday. But beyond that time...
the models diverged with the cooler GFS and warm European model (ecmwf) out of
phase. The operational Canadian solution was somewhere in between
with a ridge offshore and a weak trough centered over Oregon. The
GFS ensembles showed more normal conditions late in the week
through next weekend. At this time will not make changes to the
forecast beyond Wednesday. Albrecht
Aviation...southerly flow aloft today will become northwest on Monday as an
upper trough moves through the region. This morning the air is dry
and stable except for marine layer stratus and fog
coast...Strait...and parts of SW Washington. There are scattered
thunderstorms over Oregon this morning and the air over western Washington
will become unstable this afternoon with some moisture and scattered
thunderstorms as well...mainly over the Cascades.
Ksea...light northerly surface winds will pick up this afternoon before
switching to southerly around 05z this evening. Middle and high clouds are
likely this afternoon and tonight...convective debris from scattered
thunderstorms. There is a chance that a thunderstorm may pass over
Seattle late this afternoon or evening.
Marine...there is a nice north breeze on Puget Sound sound this morning
so updated the forecast to north 10-15kt...that was the 930am
correction to the coastal waters forecast. The fog and low clouds inched in a little
further this morning...made it down through Admiralty Inlet and into
northern Hood Canal...and got across whidbey...but it wont last more than
a few hours this morning. The fog in the Strait should burn
off...but the coast will stay in the marine layer. There is high
pressure offshore and lower pressure inland and that will continue
to produce Small Craft Advisory level winds each afternoon and
evening in the Strait. The canadians have a Gale Warning up...so
this is probably an example of when Ediz Hook gets up to 20kts while
Race Rocks peaks closer to 35kt with something like 20-30kt for most
areas...a high end Small Craft Advisory for now. The stratus layer
on the coast will bring fog and low clouds down the Strait again
tonight...and possibly into southern Puget Sound sound. If the hqm-sea gradient
really ramps up this afternoon we might even need a Small Craft
Advisory for the south Puget Sound sound area late this afternoon and
Washington...red flag warning in effect from 5 PM this afternoon until 8 am
Monday for the east portion of North Cascades National Park/
Lake Chelan National recreational area.
Heat advisory in effect until 6 am Monday for much of the
Puget Sound sound region and southwest interior.
Pz...Small Craft Advisory in effect from 3 PM this afternoon until
7 am Monday for the central and eastern Strait of Juan Delaware
For the graphical afd...visit