Area forecast discussion
National Weather Service Seattle Washington
330 am PDT Sat may 25 2013
Synopsis...a weakening low pressure system will remain over the
region through this weekend but there will be a trend toward less
showers...more sunshine...and warmer afternoon temperatures. A weak
system may lift north through western Washington on Memorial Day.
Rain will increase from south to north during the afternoon and
evening. Expect scattered showers and cooler weather through at
least midweek.
&&
Short term...western Washington is still under the influence of the
spiraling upper level low that has been over the region for the
past several days. The main low center is over southern
Alberta...but it looks like there is a second /weaker/ center over
Washington. As a result...we will continue to see isolated to scattered
showers across the region today. Probability of precipitation are highest over the southern
portion of the County Warning Area /where the flow is westerly/. Temperatures are rather
tricky under this pattern. A few sunbreaks and we will see lower 60s
but areas stuck under the clouds will remain in the 50s. This
secondary vorticity lobe over Washington will maintain a chance of showers across
the region tonight.
Showers will decrease on Sunday as the broad upper level low finally
exits to the east. Showers will mainly affect the mountains and
south part during the morning and early afternoon. But as we head
into the late afternoon and evening hours we should see showers
diminishing across the board.
Models are still waffling with the strength and timing of the next
system slated for Memorial Day. It now looks like this system
will lift north through Oregon during the morning...with rain
reaching the coast and south part of the County Warning Area during the afternoon.
The upper level trough will then cross through western Washington during the
evening for an increasing chance of showers. This system does weaken
as it moves inland so will still stick with lower probability of precipitation. Model quantitative precipitation forecast is
up to one quarter of an inch for the coast and south part...with
only a few hundredths Seattle northward. 33
Long term...models continue the trend of cool and showery weather
across western Washington through at least the middle of next week. Wednesday may
be the wettest day as a negative tilt trough axis lifts north
through the state. But the models are advertising a break in the
action starting Thursday as a broad upper level ridge over the NE
Pacific nudges inland. This pattern may continue on Friday and into the
weekend. So if this holds then look for drier weather throughout
this period. 33
&&
Aviation...weak upper level trough remaining over western
Washington today with light southwesterly flow aloft. Light low
level flow as well. Air mass moist and slightly unstable.
In general...ceilings in the 4000 to 6000 foot range with ceilings
as low as 1500 feet near showers. Some brief scattering out of the
cloud deck possible throughout the day.
Ksea...S wind 4 to 8 knots today. VFR ceilings expected...dropping to
MVFR briefly during showers. Felton
&&
Marine...light gradients today as a weak surface low over the
offshore waters moves southeast and dissipates. Light onshore flow
developing on Sunday. The next organized front reaches the waters on
Monday with small craft winds possible over the coastal waters.
Onshore flow pattern will resume for Tuesday and Wednesday. Felton
&&
Sew watches/warnings/advisories...
Washington...none.
Pz...none.
&&
$$
You can see an illustrated version of the forecast discussion at
www.Weather.Gov/Seattle/gafd/latest_webafd.Html
