Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
830 PM PST Wednesday Jan 28 2015
Synopsis...a weak upper disturbance will move inland tonight for
isolated light showers. An upper ridge will provide dry and mild
weather Thursday through Saturday. A front will bring rain back to
the area Sunday and early next week.
Short term...a broad upper ridge will be over the area tonight with
low level offshore flow. A weak disturbance in the southwest flow
aloft could bring some sprinkles tonight but this is looking less
and less likely based on radar along with the fact the latest nam12
and hrrr models which show dry weather all night. There will
probably also be some fog tonight although clouds coming up from the
south will likely prevent this from becoming too prevalent.
The upper ridge will remain over the area Thursday through Saturday
for dry weather. Low level offshore flow will also prevail during
this period. Highs will be a little above normal each day...mostly
in the 50s...with a slight warming trend through the period.
Long term...previous discussion...a warm front will bring some rain
to the area on Sunday as it moves inland. But this system is looking
slower and weaker with each new model solution. A wetter Pacific
frontal system will then reach the area on Monday for another shot of
rain. Snow level are a little lower with this system around
4000-5000 feet. The GFS tries to build another ridge over the region
Tuesday and Wednesday. The European model (ecmwf) however steers some moisture our way for
wetter weather pattern. Confidence remains low at this point. 33
Hydrology...flooding is not expected for the next 7 days.
Aviation...a weak upper level ridge will remain over western
Washington tonight and Thursday. A surface ridge over East Washington will
maintain weak low level offshore flow. The air mass is generally dry
and stable...but surface temperature-dew point depressions at 04z
were 5f or lower just about everywhere so some patchy fog and low
stratus can be expected 08z-18z.
A very weak upper level shortwave trough just west of the north Oregon
coast at 04z will move NE across West Washington tonight through 20z. This
shortwave will spread bkn050-100 cloud layers across West Washington
overnight...making it more difficult for fog/low stratus to form. A
clearing trend for the shortwave trough moisture and whatever
fog/stratus forms is expected after 18z.
Ksea...VFR conditions are expected tonight. Middle level clouds
scattered-bkn050-100 should be present 09z-18z which should be enough to
prevent fog and low stratus from forming. However with
temperature-dew point depressions expected to reach 2-3f...some
patchy stratus is not completely out of the question. Surface winds
will be north-NE 3-7 knots. Kam
Marine...a weak surface ridge centered over eastern Washington will
maintain weak offshore flow through Saturday. Pressure gradients
across western Washington will remain weak...producing northerly
winds along the coast and through Puget Sound sound...and easterly winds
through the Strait. Winds are expected to remain less than 20
knots. The exception is the West Entrance where easterly winds will get
into the 15-25 knots range at times tonight and Thursday morning...and
possibly some other days as well.
Models bring a weak front through the area Sunday. Latest runs show
winds mostly staying below Small Craft Advisory levels with this
front. A stronger system will follow on Monday and the Small Craft
Advisory winds appear to be associated more with this system.
Pz...Small Craft Advisory West Entrance.
You can see an illustrated version of this forecast discussion at