Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
252 am PST Thursday Mar 5 2015
Synopsis...an upper level ridge over the area combined with surface
high pressure will give dry conditions through the weekend. Weak
disturbances riding over the ridge to the north of the area will
give high clouds at times. Temperatures will be mild for early
March. The upper ridge will weaken early next week with more clouds
and a chance of rain returning...possibly as early as Monday night.
Short term...a rather strong upper level ridge is centered near
130w early this morning. A surface ridge extends from around 40n
135w northeast into western Washington and southwestern British
Columbia. A loop of infrared satellite images shows a weak frontal
wave and upper level short wave disturbance riding over the top of
the ridge into haida gwaii and west central British Columbia today.
But the ridge appears to be winning out...and all we will see of
this system through early Friday will be middle and high
clouds...mainly over the northern half of western Washington. Rain
chances were taken out of the forecast for today through early
Friday over northern portions of the area. Despite the
clouds...expect temperatures today to be mild with highs in the 50s.
The upper ridge will rebound over western Washington on Friday and
pressure gradients will remain rather flat. The air mass aloft on
Friday will be rather mild with 850 temperatures around +6c. Lowland
temperatures near the Cascades and Olympics and from about Seattle
southward will rise to around the 60 degree mark.
On Saturday...the ridge will become negatively tilted as a weak
short wave trough drops from west central British Columbia southeast toward
Montana and Wyoming. The passage of this trough will likely do
little more than bring some wispy high clouds through the area...and
temperatures are likely to rise back to Friday levels. Albrecht
Long term...Sunday will remain dry as the upper ridge remains over
the area and pressure gradients remain flat. Sunday high
temperatures will rise about a degree or two above Saturday values
and will cap off a really nice early Spring weekend for western
Starting on Monday...the upper ridge will start to shift east and
weaken as Pacific moisture and energy starts to move back onto the
West Coast. Monday will likely remain dry but will be a transition
day as middle and high clouds increase and temperatures drop back into
Models are beginning to show more of a split flow along the West
Coast for Tuesday into Wednesday with the northern stream over
British Columbia and northern Washington and the southern stream
moving into mainly California into central Oregon. The European model (ecmwf) shows
the southern stream farther north and dominant while the GFS shows
the northern stream more in control from about Washington northward.
At this time the best bet is to keep clouds in the forecast with a
chance of rain Monday night Onward with temperatures near normal for
early March. Albrecht
Hydrology...flooding is unlikely for the next 7 days.
Aviation...high pressure aloft will persist over the Pacific northwest. A weak
upper level system will push across southern b.C. Today and
tonight...bringing high clouds into western Washington at times. Light westerly flow
aloft. Dry in the lower to middle levels. Stable atmosphere.
Ksea...NE wind 4-6 knots becoming northwest in the afternoon. High clouds at
times with VFR conditions.
Marine...surface high pressure over the Pacific northwest will result in weak
pressure gradients and light winds through the weekend. Weak onshore
flow may develop Sunday night. A front may reach the waters by
You can see an illustrated version of this forecast discussion at