Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
903 am PST Wednesday Dec 4 2013
Synopsis...a cold and dry pattern will continue over the next
several days. There is a chance of very light snow or flurries
Thursday night...and another chance of light snow late this weekend
and early next week. Temperatures may begin to moderate across the
region by next Tuesday.
Short term...bitter cold conditions across western Washington this morning.
Temperatures are mainly in the 20s but there are teens in the SW interior
and Hood Canal. There is a small patch of stratus over the north
sound otherwise skies are clear. Highs today will only be in the
30s. Expect another cold night tonight.
A high amplitude ridge offshore will maintain northerly flow aloft
on Thursday. The low level flow will remain offshore with a dry air
mass near the surface. Models show an increase in middle/high level
clouds as a weak upper level disturbance clips the area Thursday
afternoon an evening. The energy in heading into Oregon so western Washington
is still looking dry. But we may see a few flurries float out of the
middle level cloud deck. This trough will exit Friday morning with skies
clearing once again. 33
Long term...previous discussion...Saturday will be a sunny but
rather cold day. Highs again are not likely to reach the freezing
mark again...with 20s and teens in the colder spots overnight. A
shift in the upper air pattern is expected to begin on Sunday. The
latest 00z runs have all trended toward pushing the ridge eastward and
gradually modifying the air mass. Latest models bring a weakened
system through the upper ridge and into western Washington late Sunday or
Monday. Some previous model runs were more aggressive with bringing
a short wave down from the north and phasing with southern stream moisture.
More likely than not some light snow will develop sometime late in
the weekend or Monday...then change over to rain Monday or Tuesday.
At this point...there is poor model run to run consistency so no
changes were made to the extended. How quickly the air mass modifies
will depend on how much lowland accumulation might occur...if any.
Hydrology...river flooding is not expected for the next 7 days.
Aviation...dry northerly flow aloft and at the surface will
continue over Washington today. The air mass will remain cold dry
and stable. VFR clear conditions are expected. Some patchy fog in
the southwest and a bit of stratus over Puget Sound sound will persist for
a few hours this morning but should be gone by 19z.
Ksea...VFR clear. Winds will be northeast less than 10 knots. Chb
Marine...Small Craft Advisory strength northeast winds continue
over the northern inland waters this morning. They should fall below
20 knots in the afternoon. Winds over all other waters have subsided
below 20 knots. A weak weather system is forecast to move south off the
coast on Thursday. This will shift the winds to southerly.
Winds will return to northerly and offshore Friday and Saturday.
Gale force northeast winds are possible at the West Entrance and
over the northern inland waters Thursday night and Friday. Chb
Pz...Small Craft Advisory northern inland waters.
You can see an illustrated version of the forecast discussion at