Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
320 PM PST Friday Dec 6 2013
Synopsis...cold and dry weather will continue tonight through early
next week...with some of the coldest temperatures of the year
tonight and Saturday night. Temperatures will begin to moderate
across the region next Tuesday and Wednesday as the low level flow
becomes more onshore. Snow or mixed rain and snow is possible Monday
through Tuesday until the precipitation becomes all rain Wednesday.
Short term...weak weather system that nonetheless brought a few
inches of snow to the coast has now moved south out of the area.
Skies are mainly clear except for some lingering high clouds over
the south. These too should clear tonight. Clear skies and a cold
air mass over the area will bring very low temperatures tonight with
lows in the teens...low 20s near the ocean. Windy conditions will
continue tonight over the far north interior and near the West
Entrance and a Wind Advisory remains in effect there.
Saturday will be cold and sunny. All guidance agrees...highs are not
likely to reach 30 degrees. Saturday night will probably be a few
degrees colder than tonight. Will issue a Special Weather Statement
to highlight the low temperatures...which are near record lows in a
Used the NAM solution for Sunday. This brings a weak system south
along the coast and drops a little snow there. Skies will be mostly
cloudy on the coast and partly sunny inland. Highs will rise a few
degrees from Saturday but will still mostly be below freezing.
Overnight lows will also be higher.
GFS and Euro solutions differ for Monday with the GFS dry and the
Euro bringing light precipitation inland. Went with the Euro and its
cloudiness and low probability of precipitation. With the 1000-850 mb thickness well below
1300m...any precipitation Monday will be in the form of snow.
Amounts should be pretty light...less than an inch. Burke
Long term...Tuesday looks like the transition day. A weak system
will move inland bringing a little precipitation. Thicknesses rise
above 1300m over most of the area except for the far north.
Typically the Hood Canal area also does not warm in these scenarios.
In any case precipitation is again pretty light. If the transition
does occur the day could begin with a little snow and end with a
little rain or mixed precipitation. The Hood Canal area and far
north would remain in snow and perhaps get a few inches. Still
pretty far out to be making these bold predictions however.
Wednesday looks fairly dry but kept chance probability of precipitation in the forecast with
likely probability of precipitation on the coast as the next system moves toward Washington.
The air mass should be warm enough for just rain by Wednesday. The
system arrives Thursday and Friday looks showery. Temperatures are
forecast to be back to normal by then. Burke
Hydrology...river flooding is not expected for the next 7 days.
Aviation...northerly flow at the surface and aloft will persist
overnight. The strongest flow will be in the lower levels during
much of this period...although the winds aloft will strengthen to
45-55 knots early Saturday. VFR conditions are anticipated across the
Ksea...east or northeasterly winds of 9-15 knots will continue through much of
tonight. VFR conditions will continue.
the combination of temperatures in the 20s and strong Fraser outflow
will result in the continuation of light freezing spray across the
northern inland waters...especially tonight. Freezing spray is also
most likely in the bays and near inlets. Anticipate ice accumulation
rates of about 0.02 to 0.10 of an inch per hour through early Saturday
A 1045 mb high over central British Columbia and lower pressure off the
Oregon coast will result in continued strong NE or offshore flow
tonight. The high over British Columbia will weaken and move southeast on
Saturday for decreasing offshore flow. The offshore flow will weaken
further Sunday as lower pressure develops over the Washington coastal
Washington...Wind Advisory remains in effect until 4 am Saturday for the far
north interior and western Strait of Juan Delaware fuca.
Pz...freezing spray advisory remains in effect until 10 am Saturday
for the northern inland waters.
Gale warnings remain in effect for the coastal waters from
Cape Flattery to James Island out to 60 nm and the West
Entrance to the Strait of Juan Delaware fuca.
Small craft advisories remain in effect for the remaining
waters except the Admiralty Inlet.
For the graphical afd...visit