Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
415 am PST Sat Mar 8 2014
Synopsis...another strong frontal system will affect western
Washington today into Sunday morning with rain...high snow
levels...and locally windy conditions. An upper trough will move
through on Monday for cooler showery weather. A strong upper ridge
will provide dry and mild weather Tuesday and Wednesday.
Short term...satellite imagery shows another juicy front just off
the Washington coast this morning. Multiple waves rippling up the
back side of the front has slowed its eastward progress overnight
with no rain being reported yet. Temperatures under cloudy skies at
3 am were in a wide range...from near freezing at Shelton to near 50
at NAS Whidbey Island.
Rain starting on the coast this morning spreading inland late
morning into the afternoon hours. Satellite analysis from NESDIS
indicates moisture from Typhoon Faxai embedded in the front. Latest
qmorph rain rates show two bullseyes of 1 to 1.5 inches in 6 hours.
One near 50n/129w and the other near 36n/141w. Model 850 mb winds
ahead of the front still in the 50-60 knot range out of the
southwest resulting in more heavy rain for the south slopes of the
Olympics this afternoon into the early evening hours in addition to
windy conditions along the coast. 12 hour rainfall amounts between
18z and 06z could be as high as 3.5 inches. Lesser amounts expected
in the Cascades with an inch to 2.5 inches possible. Significant
rains in The Lowlands as well with a half inch to 1.25 inches in the
12 hour window. With the ground already saturated from recent heavy
rains the threat of landslides remains intact. Warm air out ahead of
the front will push snow levels up into the 7000-8000 foot range
making the precipitation rain over all but the higher peaks.
Rain continuing later tonight into Sunday morning with the rain
rates decreasing significantly after 06z tonight. Cold front moving
through the area Sunday morning. Onshore flow behind the front will
keep a chance of showers in the forecast but most of the shower
activity will be confined to the mountains and a possible Puget Sound
sound convergence zone near the East Entrance of the Strait.
Threat of showers continuing Sunday night into Monday morning with
an upper level trough moving through the area. By Monday afternoon
the trough axis will be east of the Cascades with just some
lingering showers especially in the Cascades and once again in the
possible convergence zone north of Seattle.
Long term...after a record wet start to March a Little Break in the
precipitation looks to be in store for the area with an upper level
ridge building off the coast Tuesday and surface high pressure
building into western Washington. Upper level ridge axis moves
inland Tuesday night into Wednesday with the low level flow turning
offshore keeping dry weather in the forecast for Wednesday. Extended
models continuing with the trend of push the upper level trough
further north for Thursday. Will stay with chance probability of precipitation for now but
there is certainty a chance the area could see three dry days in a
row. Upper level ridge well to the east by Friday with a well
organized system moving into the area later Friday into Saturday.
Temperatures will remain near normal through the period. Felton
Hydrology...a Flood Warning continues for the Skokomish River at
Potlatch for minor flooding. The river fell below flood stage last
night but with the possibility of 3 plus inches of rain in a 12
hour period later today into tonight for the south slopes of the
Olympics the river is forecasted to rise back above flood stage
On the Chehalis river...the river at Porter is in the process of
cresting just 0.3 feet below flood stage. The crest will move down
into the lower reaches of the river in Grays Harbor County today.
With the river close to flood stage will keep the watch going for
the lower Chehalis.
Moderate rain with a few hours of heavy rain are expected on later
this afternoon into tonight with snow level 7000 to 8000 feet
leading to renewed rises on all area rivers. Currently the only
Flood Warning is for the skokomish but the more flood prone rivers
like the Puyallup at Orting will need to be watched. Other rivers
that came close to or did go over flood stage this last round like
the Cowlitz at Randle and the Snoqualmie at Carnation also bear
Aviation...a frontal system just offshore will move inland across West
Washington through this evening. The cold front should cross the coast
around 02z and then the interior around 04z. Strong low level S-SW
flow aloft will develop over West Washington today...with gusty surface winds
developing along the coast and over the north interior areas. Rain from
the frontal system will gradually lower ceilings from VFR this morning
to MVFR on the coast after 18z and over the interior around 00z.
MVFR to IFR conditions should persist through Saturday night.
Ksea...good VFR conditions will continue through around 18z with
just middle-high level moisture over the area. Surface winds will be
S-southeast 3-7 knots. Rain from the approaching frontal system will reach the
area after 18z with ceilings gradually lowering. MVFR ceilings expected
after 00z. Low level winds aloft fl050-fl100 will increase to 35-45
knots after 15z and to 40-50 knots after 21z. Kam
Marine...the frontal system approaching the Washington coast today is
expected to raise gales over the coastal and northern interior
waters today. Latest 00z models were slightly weaker with the winds
and did not have the gales extending quite as long. The front should
cross the coast early this evening...then the interior waters by middle
A Small Craft Advisory was issued for Admiralty Inlet today. Small Craft Advisory
winds could also affect north Puget Sound sound up near Everett this
afternoon...but this is not quite as certain. A Small Craft Advisory could be issued
later this morning.
Models were also weaker with the onshore flow pattern developing
behind the cold front on Sunday. Rather than building in from the
west a weaker ridge seems to build right along the coast. The
forecast was nudged a bit above model guidance so that Small Craft Advisory winds are
advertised for the central and east Strait on Sunday. The model
variability does not lend much confidence to this part of the
The onshore flow weakens briefly Sunday night as an upper level
trough crosses the area...then strengthens again on Monday as a
large surface ridge approaches from offshore. The ridge will move
over West Washington Tuesday and Wednesday. Kam
Washington...flood watches are in effect for parts of the County Warning Area.
Pz...Gale Warning coast...entrances to the Strait an north inland
Small Craft Advisory Admiralty Inlet.
Small Craft Advisory for rough Grays Harbor bar.
You can see an illustrated version of the forecast discussion at