Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Seattle Washington
928 PM PDT Sat Sep 20 2014

Synopsis...high pressure aloft over the region will move east
with time...allowing a weak low pressure system to move across
the area on Monday. A stronger system will impact the region the
middle of the upcoming week...promising wet and breezy conditions.


Short term...
an upper ridge over the region will continue moving east...
allowing a broad upper trough over the northeast Pacific to
approach the region. Look for the low level offshore flow to
become onshore by midday Sunday. This will allow stratus to surge
north along the coast Sunday morning. Expect increasing clouds
Sunday night across the County Warning Area due to strengthening low level onshore
flow and the approaching upper trough.

Expect a short wave trough to move across the area on Monday. The
associated occluded front will likely dissipate as it moves
onshore. The best chance of precipitation will be on the coast with this

A stronger and wetter low pressure system will impact the region
on Tuesday for a better threat of rain across the entire County Warning Area as well
as an increase in wind.

Long term from the previous discussion...
Tuesday night and Wednesday will be the period of time when
western Washington is likely to have period of rain as a stronger frontal
system moves slowly through the region. There might be two surges
of fairly strong southerly flow Tuesday evening...and
another later Wednesday or Wednesday night and Tuesday-Thursday do not look like a good
time to be camping or hiking...especially in the Olympics. There
will be a broad upper trough centered around 140w Tuesday. GFS
height falls associated with the frontal system stretch and Peter
out in the GFS which was not nearly as wet as the European model (ecmwf). Both
models showed the heaviest rain coast and Olympics. After a wet
period...the main upper trough is likely to drop south Thursday and Friday
into calif/NV. The GFS and Euro solutions diverged late in the
week...the Euro kept a weakening upper trough over the west with a
chance of showers while the GFS was faster with an approaching
upper ridge with a better Prospect for dry weather by next


Aviation...southwest flow aloft with an upper level trough over the
northeast Pacific and an upper level ridge over The Rockies. At the
surface...a trough along the coast will shift inland Sunday. Air
mass dry and stable.

Stratus pushing north up the West Coast should reach the Washington
coast Sunday morning as onshore flow develop. There should also be
some fog Sunday morning in sheltered valleys.

Ksea...clear skies. Northerly wind 4-8 knots will become southerly
Sunday. Schneider


Marine...offshore flow will switch to onshore Sunday as a trough
along the coast moves inland. A weak front will move through the
waters on Monday. A stronger frontal system will arrive Tuesday and
Wednesday. This system could bring gale southerly winds to the
coastal waters. Schneider


Sew watches/warnings/advisories...
Pz...small craft advisories are in effect for the coastal waters
and Strait of Juan Delaware fuca.




You can see an illustrated version of this forecast discussion at

National Weather Service Glossary of Abbreviations