Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus66 ksew 172154 

Area forecast discussion
National Weather Service Seattle Washington
254 PM PDT Sat Aug 17 2019

Synopsis...onshore flow into Monday as a weak weather system
passes to the north of western Washington. An upper level ridge
will strengthen early next week for warmer temperatures and more
sun. A front is expected around the middle of the week with a
chance for showers and cooler temperatures.


Short term /tonight through Tuesday/...satellite imagery this
afternoon shows mostly cloudy skies across western Washington
with some clearing in spots. Generally dry conditions into Sunday
with just a slight chance for a few showers mostly across the
olympic peninsula as a system slides by north of the area.
Temperatures through the weekend will be a few degrees below
normal with highs in the mid 60s to mid 70s across the area.

An upper level ridge will build into the region on Monday with
weak offshore flow by Monday afternoon. Expect additional sunshine
Monday afternoon after morning stratus clouds. Temperatures will
also be a few degrees warmer in the 70s with offshore flow.

The upper level ridge will start to slide east of the area into
Tuesday ahead of the next system. Although there may be some
stratus clouds Tuesday morning, they will be less widespread given
the generally weak offshore flow Tuesday morning. Dry weather into
Tuesday afternoon with showers along the coast by Tuesday night as
the front approaches. Temperatures on Tuesday will be warmer given
the ridge placement and weak offshore flow with highs in the 70s
to mid 80s in spots across the area. Jd

Long term /Wednesday through Saturday/...the front will move
onshore Wednesday with some showers around as the system slides
through the area. Guidance is in general agreement on the timing
of the system with the GFS being a tad bit wetter, especially
across the northern tier, than the European model (ecmwf). Either way, expect
showers around Wednesday with generally drier weather by Thursday
morning. Flow aloft following the system looks mostly zonal with
guidance suggesting another chance of some pops Friday or
Saturday. Temperatures are expected to be near climo into the 70s
across the area. Jd


Aviation...weak low level onshore flow continuing through the
weekend. Northwesterly flow aloft becoming westerly on Sunday.

Clouds continue to linger over West Washington this afternoon. There has been a
bit of improvement with some gradual lifting of cloud bases...with
most locations reporting VFR conditions and those that are not are
only a couple of hundred feet away from criteria. Like yesterday at
this time...current satellite trends do not show much in the way of
improvement and as such...this will likely be as good as it gets for
the remainder of this afternoon and into this evening before cigs
start to drop once more during the overnight hours as stratus will
once again return by Sunday morning. Sunday looks like another day
similar to the past two...with some gradual improvement and cigs
climbing back into high end MVFR to VFR conditions by mid afternoon
but never really clearing out.

Ksea...lowest level of clouds might flip-flop between broken and scattered
this afternoon and evening around 3000 ft but mid level clouds
around 5000 to 6000 ft will likely remain broken or overcast. Cigs lowering
tonight with stratus Sunday morning similar to the previous two
mornings per the current pattern...cigs gradually
increase late morning into mid afternoon. Winds
remaining generally south to southwesterly 4 to 8 knots. Smr


Marine...weak onshore flow will continue through the
weekend. Surface flow becoming light Monday and Tuesday with a
weakening front on Wednesday. Model output still suggesting Small
Craft Advisory winds possible over the coastal waters as the front
reaches the area while remaining waters look to have winds remain
fairly benign and well below any headline criteria. Smr


Hydrology...the daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
until then.


Sew watches/warnings/advisories...

National Weather Service Glossary of Abbreviations