Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
935 PM PDT Friday Apr 17 2015
Synopsis...high pressure aloft will prevail over the region
through Monday for dry weather with above normal temperatures.
Anticipate cooler and unsettled conditions Tuesday through the
end of next week.
Short term...satellite imagery shows a small area of SC over the
central sound this evening. Stratus along the central coast earlier
today has moved south and offshore this evening. Smoke from fires in
Siberia also over the area this evening. Temperatures at 9 PM were
in the upper 40s to near 60.
Upper level ridge building offshore overnight into Saturday morning
with what little cloud cover that is over the area this evening
dissipating. Northerly surface gradients not strong enough to
completely eliminate the possibility of fog in the fog prone
locations like the southwest interior early Saturday morning. Lows
overnight will be in the upper 30s and 40s.
Sunny weather in store for Saturday with the upper level ridge over
the area. Patchy morning fog will be shallow and burn off quickly.
Temperatures aloft do not warm up very much on Saturday...850 mb
temperatures go from around plus 6 to plus 8c...with the upper level ridge
axis still offshore by 00z Sunday. This combined with the
continuation of the northwesterly surface gradients will keep highs
on Saturday just a couple of degrees warmer that Friday with 60s and
lower 70s forecast.
Little change in the pattern Saturday night and Sunday with the
upper level ridge axis remaining offshore and the surface gradients
remaining northwesterly. Temperatures aloft continuing with the
gradual warming trend with 850 mb temperatures near plus 10c by 00z Monday.
With a couple of degrees more of warming the warmest locations will
get into the middle 70s on Sunday with 60s and lower 70s elsewhere.
Upper level ridge axis shifting inland on Monday with the
northwesterly surface gradients weakening. Temperatures aloft show
little change versus Sunday. For now a persistence forecast looks
good for Monday with the possibility of a couple more degrees of
warming if the afternoon northerlies are slow to kick in. Current
forecast on track. No updates this evening. Felton
Long term...previous discussion follows.
The medium range solutions were in more or less agreement that an
upper trough will become the dominant feature over the western USA.
The primary difference between the models were in the details.
Anticipate cooler and unsettled conditions during this period.
Aviation...an upper level ridge over the NE Pacific will nudge east
into western Washington for dry and stable weather. The flow aloft is
northwesterly. VFR conditions are expected...although may see patchy
shallow fog Saturday morning in the south sound and coast.
Otherwise...high pressure will remain in control through Saturday
for clear skies. 33
Ksea...VFR conditions will continue tonight. Sct050 clouds will exit
this evening for clear skies. Expect north/NE winds to 10 knots. 33
Marine...onshore flow will ease across western Washington tonight. Gales
have ended in the Strait but will continue to see Small Craft
Advisory winds through at least midnight tonight. Models continue to
show northwest winds of 15 to 25 knots through the Strait of Georgia and a
Small Craft Advisory is in effect for the northern inland waters.
Low pressure along the coast will maintain northerly flow Saturday
and Sunday. Offshore flow will continue through Monday. The next
front will arrive Tuesday afternoon or evening. 33
Pz...Small Craft Advisory coastal waters...Strait of Juan Delaware
fuca...northern inland waters...Admiralty Inlet.
Small Craft Advisory for rough Grays Harbor bar.
You can see an illustrated version of the forecast discussion at