Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
850 PM PST Tuesday Mar 3 2015
Synopsis...upper level ridging and low level offshore flow will
maintain dry and generally mild conditions Wednesday. The exception
will be chilly overnight lows tonight. A weak system will brush the
area Thursday bringing clouds and a chance of rain mainly to the
north. Rebounding ridging aloft and low level offshore flow Friday
will return fine weather to the area through the weekend.
Short term...minimal cloud cover and light northerly winds will
produce chilly low temperatures again tonight...especially in sheltered
locations away from the water. Expect lows to dip into the upper 20s
for many locations again tonight. The upper level ridge along 135w
will continue to shift east and tilt into British Columbia and
Washington Wednesday and weaken Wednesday evening as a weak upper
level short wave trough passes over the ridge axis. The primary
impact with this system will be increasing clouds and a return to
onshore flow that will result in warmer overnight temperatures.
There remains a chance of rain for the northernmost portion of the
area as the upper level trough and associated front brush the region
Thursday and Thursday evening.
Long term...the upper level ridge will rebound inside of 130w
Friday as the upper level trough ejects into Alberta an Montana. In
what has become a fairly familiar pattern as of late...surface high
pressure will once again build into eastern British Columbia
supporting mild offshore flow and sunshine over much of the area
through the weekend. Highs temperatures will rise into the middle 50s
to lower 60s while overnight lows will hover around 40 through the
weekend. Medium range models are fairly consistent in showing the
upper level ridge shifting onshore Saturday and Sunday...then
weakening somewhat Monday as another weak system slides into British
Columbia from Alaska. Both the GFS and European model (ecmwf) hint a chance of
precipitation Monday or Tuesday as this system brushes the
area...with a more consolidated system midweek.
Hydrology...flooding is unlikely for the next 7 days.
Aviation...northerly flow will prevail over western Washington tonight and
Wednesday. The air mass is dry and stable. The south sound may see
patchy shallow fog overnight...otherwise VFR conditions are
Ksea...light north/NE winds at the surface to 5 knots. Clear skies and VFR
conditions expected through Wednesday. 33
Marine...high pressure east of the Cascades and weak low pressure along the
coast will give light offshore winds across western Washington tonight.
Winds over the waters will be generally light through the end of the
week with high pressure over the area. 33
You can see an illustrated version of this forecast discussion at