Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
900 am PDT Friday Oct 24 2014
Synopsis...offshore surface flow and a weak ridge aloft will keep
western Washington dry today. Rain will spread from south to north
tonight. A filling low pressure center will move across the area
Saturday night...bringing rain and locally windy conditions. Wet and
breezy conditions are likely at times next week.
Short term...today will be a quiet and mainly dry day as the area
is between systems. Offshore surface flow will continue today then
increase tonight as a deep low pressure system develops off northern
California and moves northeast. A Wind Advisory is in effect tonight
for east winds over the east Puget Sound sound lowlands. Rain will spread
from south to north tonight as a warm front passes. Amounts are
likely to be pretty light east of Puget Sound sound where the offshore
flow will make the air mass drier.
On Saturday afternoon the low...now filling...will reach the central
coast. It will move inland Saturday night. Rain along with breezy to
windy conditions are likely after midnight over most areas. On
Sunday high pressure will start to build and Sunday night looks calm and
drier. Temperatures will be seasonal all three days. Burke
Long term...previous discussion...a lull or break in precipitation
is possible on Monday but the next system will be quickly
approaching. The 00z models have trended stronger with the next low
pressure system which contains the remnants of an excessive-tropical
system. Fortunately it will be progressive which will help limit
rain amounts. There will be a lot of gradient with this low and
locations prone to southeast wind...like Whidbey Island northward...could see
some strong winds on Tuesday. Models weaken the low as it crosses
near or just north of Washington so strong winds are not expected over other
inland areas at this point.
Yet another low pressure system looks set to arrive middle week. Models
diverge on the long wave trough position by Thursday so it is
difficult to tell whether additional systems will affect our area.
The European model (ecmwf) shifts the trough further offshore and the GFS is more
aggressive keeping a trough over the Pacific northwest. Mercer
Hydrology...flooding is unlikely over the next 7 days.
Aviation...southwest flow aloft will continue over western
Washington through tonight as a Pacific frontal system approaches
the region. The air mass will become moist all levels this evening
as a warm front moves into the forecast area from the south.
Mainly VFR conditions prevail across the area this morning with sky
cover scattered-bkn035 sct-bkn120. However isolated fog with LIFR
conditions will persist in the south Puget Sound sound region and
southwest interior for the next couple hours. Rain will spread from
south to north across the forecast area this evening and tonight...
with conditions deteriorating to widespread low-end MVFR and areas
of IFR by Saturday morning.
Ksea...light wind becoming northeast 5-12 knots..and occasional
easterly gusts to 20 knots are possible tonight. Conditions will likely
deteriorate to low-end MVFR and occasional IFR in rain and fog
Saturday morning. Mcdonnal
Marine...high pressure over southeast British Columbia and a
developing low off the northern California will result in northeast
offshore flow today. The warm front associated with the low will
move north through western Washington tonight...and the low will
track northeast into the western Washington interior late Saturday
afternoon. This feature should produce Small Craft Advisory winds
late tonight through Sunday morning. Gales are possible but unlikely
over the coastal waters.
High pressure will build over the region from the southwest on
Sunday and remain over the area Monday. Another Pacific frontal
system and its developing low will produce Small Craft Advisory or
possibly gale force winds over the area Monday night and Tuesday.
Washington...Wind Advisory for the east Puget Sound sound lowlands tonight through
Wind Advisory for Bellevue and vicinity tonight.
You can see an illustrated version of this forecast discussion at