Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 171714

Area Forecast Discussion
National Weather Service Seattle WA
915 AM PST Fri Feb 17 2017

.SYNOPSIS...Weak high pressure aloft will bring dry weather to the
area today. A weather system moving from the south will clip the
region Saturday, giving a chance of rain. A series of weak weather
systems will move through the area Sunday through Wednesday.


.SHORT TERM...Satellite imagery shows a mix of clouds and sun over
western Washington this morning. Radar shows scattered showers on
the coast but none inland. Gradients are reversing and there will be
light northerly winds by afternoon. Current forecast has this well in
hand. Highs today will be in the low to mid 50s.

Tonight will be dry, then a weak weather system will clip the area
Saturday. The new NAM limits rain to the mountains and coast, with
the Puget Sound area remaining dry. May adjust pops to reflect these
ideas. Saturday will be cloudier than today, and highs will be
around 50.

After another short break in the weather Saturday night, the next
weak system will arrive from the southwest on Sunday. Pops are
mostly in the likely category with highs around 50. Burke

.LONG TERM...Previous discussion...extended models in good agreement
with the jet to the south of the area Monday and Tuesday and western
Washington getting the northern portion of the systems moving inland
along the west coast. Upper level trough moving through the region on
Wednesday keeping chance pops in the forecast. Another trough moving
down from the north on Thursday keeping a chance of showers in the
forecast. Highs will be a few degrees below normal during the the mid 40s to near 50. Felton


.AVIATION...SW flow aloft will continue over W WA through 12Z
Saturday, in-between an upper level ridge over the Rockies and an
upper level shortwave trough approaching the area from offshore. The
air mass is generally dry and good VFR conditions with mainly high
clouds are expected throughout W WA by 20Z. At 17Z there was still
some patchy IFR fog/stratus over south Puget Sound and the SW
interior, mainly KPWT-KSHN-KOLM-KCLS, and some spotty MVFR stratus
over the N interior N of KNUW. These lower conditions should
dissipate by 20Z. A mid level layer BKN100-120 is expected to
gradually spread N over W WA after 00Z

KSEA...Just high clouds are expected today. A mid level layer around
BKN100-120 is expected to spread N over the terminal after 01Z.
Surface winds SE 3-6 KT are expected to shift to NE 3-7 KT after
19Z. Kam


.MARINE...A surface trough extending northward from the deep low
over central CA will bring weak northerly flow to W WA this
afternoon and tonight. The trough will fill by early Saturday
morning and will be replaced by a weak surface ridge by afternoon.
This will keep winds generally weak across the area through
Saturday. The only short term problem is residual SW-W swell around
10 feet over the coastal waters today. The resulting seas are
actually a combination of a couple of smaller swell trains, both of
which will be subsiding through this afternoon. The SCA for
hazardous seas will run through 6 PM. The SCA for rough Grays
harbor bar will end at 1 PM today.

The pattern will change on Sunday and Monday as a large upper level
trough sets up over the NE Pacific. Several systems will wheel
around the large trough. This will allow a weak surface low and
accompanying surface front will move NE across the coastal waters on
Sunday. A second weak surface low will follow on about the same
track on Monday. A third larger low is expected to track NE across W
WA Monday night and Tuesday. SCA winds are likely over the
coastal waters with these systems. Kam


.HYDROLOGY...The Skokomish river fell below flood stage and the
warning will expire this morning. The flow on the White River at R
street will remain high, and near flood flow today, but it is not
expected to go above flood flow. That warning will also expire
this morning.

USGS landslide guidance remains above the threshold at which
landslides typically occur. This means there will continue to be
an elevated threat of landslides for at least another day or two.


.CLIMATE...With another 0.50 inches of rain yesterday the monthly
total at Seattle-Tacoma airport is now 7.84 inches. Another 1.28
inches of rain is needed to break the record for precipitation for
the month of February which is 9.11 inches set in 1961. In this
water year, which began on October 1st, we have already had one
month with record breaking rainfall in Seattle, October with 10.05
inches. Felton


PZ...Small Craft Advisory coast for hazardous seas until 6 PM PST.
     Small Craft Advisory for rough Grays Harbor bar until 1 PM PST.



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