Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
345 am PST Friday Feb 12 2016
Synopsis...a weak cold front will pass through western Washington
this morning. An upper level trough will produce showers this
afternoon through Saturday morning. A pair of warm fronts will bring
rain Saturday afternoon through Sunday evening. West flow aloft will
maintain an active weather pattern into early next week.
Short term...rain associated with the warm front that passed
through the area yesterday still lingering...albeit scattered
(pic1). Main focus for today will be whether or not cold front will
gain strength as it gets closer to Washington coast as models
predict. A good vote in favor of this happening is that some
development is starting to occur along the West Coast of Vancouver
Island (pic2)...so feel safe with probability of precipitation for the morning. In the wake
of this front...an upper level trough is prognosticated to move into the area
by this evening and pass through western Washington (pic3)...crossing east
of the Cascades by Saturday morning...keeping showers in the
forecast in the wake of the aforementioned cold front.
The pair of warm fronts for the remainder of the weekend pose a bit
of a concern...with the potential for heavy rain especially along
the coast (pic4)...early Saturday evening and on the west slopes of
the Cascades Saturday night (pic5). Current forecast shows quantitative precipitation forecast
around an inch for a large portion of the olympic peninsula...which
may give rise to some Hydro concerns. Quantitative precipitation forecast amounts do diminish rather
quickly starting Sunday...which may help to offset those
concerns...but the risk of precipitation will linger for the remainder of
Flat upper level ridging may bring a brief pause in precipitation for
Monday...although GFS (pic6) is a bit more optimistic than European model (ecmwf).
Still...was Happy for any chance to drop probability of precipitation back into chance
Snow levels generally remaining high for the short term...although
will fall starting tonight and reaching their nadir around 3500 feet
Saturday before rebounding Saturday night. This trend is also
applicable to temperatures...as Saturday looks to be the coolest with
lowland highs around 50...then bouncing back to middle 50s Sunday and
Models remain in fair agreement for the short term...aside from
disagreement regarding Monday previously mentioned...thus no major
changes to the forecast. Smr
Long term...Monday only proves to be the start of the divergence in
the models. Starting Tuesday...it looks like dominant weather
factors will be a pair of lows out over the Pacific...one prognosticated to
go north of western Washington into Canada...the other...well...that depends
on which model to believe. And even then...GFS and European model (ecmwf) have traded
solutions in the past 24 hours. GFS now favors wetter solution with
southern low coming on shore off the Oregon coast while European model (ecmwf) now
has low going into California...which would keep the County Warning Area not
entirely dry...but precipitation would be more scattered. Needless to
say...this does not put a great deal of confidence in the extended.
Thus...like previous dayshift...have opted for broad brush probability of precipitation over
the area until a solution gels between the two. Smr
Hydrology...river flooding is unlikely through Saturday. There is
some potential for heavy rain over the Olympics and north Cascades
beginning Saturday night which could cause the Skokomish River and
possibly a few rivers in the north Cascades to flood early next week.
Aviation...moist southwesterly flow aloft continuing today (pic10). Air
mass stable becoming slightly unstable behind cold front later this
Cold front moving through this morning. Wide variety of ceilings
ahead of the cold front ranging from near 200 feet up to around 5000 feet.
Ceilings generally settling in the 1000-2000 foot range middle morning.
Improving ceilings behind the cold front this afternoon back up into the
4000-5000 foot range except near kpae where a convergence zone in the vicinity
will keep ceilings MVFR. Little change through the evening hours.
Ksea...ceilings near 2000 feet through late morning with brief ceilings near
500 feet and visibilities 2-4sm in light rain. Ceilings improving to
4000-5000 feet this afternoon into the evening hours. Southeast wind 6 to 10 knots
becoming southerly 10-15 knots late morning. Felton
Marine...cold front moving through the waters this morning with Small Craft
Advisory southerly winds along the coast...at the entrances to the Strait...
Admiralty Inlet and the northern inland waters. Post frontal onshore flow
this afternoon into Saturday. Small Craft Advisory southerly winds
over Puget Sound sound and Hood Canal will develop this afternoon and continue into
A series of frontal systems will give Small Craft Advisory conditions to most
of the waters Sat night through early next week (pic12)(pic13). Felton
Pz...Small Craft Advisory all waters.
Small Craft Advisory for rough bar through Saturday for
Grays Harbor bar.