Scientific Forecaster Discussion
fxus66 ksew 260425
Area forecast discussion
National Weather Service Seattle Washington
925 PM PDT Sat Mar 25 2017
Synopsis...isolated showers this evening will come to an end as a
weak ridge moves across western Washington. Rain will spread
inland early Sunday as a front approaches the area. The front will
move across the area late Sunday. Onshore flow and showers will
follow the front Sunday night and Monday. A warm front will brush
the area Tuesday. A rather wet frontal system will reach the area
Wednesday. An upper trough and onshore flow will keep showers in
the forecast Thursday. Dry and mild weather is possible for the
end of the week.
Short term...a weak short wave ridge is sitting along the
Washington coast this evening. Radars show residual isolated very
light showers in the south interior and near Oak Harbor on Whidbey
Island this evening. These should dissipate by 11 PM as the
ridging moves into the area.
Infrared satellite imagery shows a frontal system that is
associated with a deep low in the Gulf of Alaska now sitting along
about 132w longitude. The front itself will move onshore late
Sunday afternoon and sweep inland by early evening. Models are
consistent in showing the rain shield ahead of the front moving
onto the coast about 12z and into the interior shortly after 15z.
Sky and pop grids are consistent with the latest model blend. With
the clouds and precipitation around the area on Sunday, expect
temperatures to struggle to get much higher than 50 degrees in
most places. Another raw March day for the area! Snow amounts
around Paradise Ranger station in Mt Rainier National Park could
be in the advisory category Saturday afternoon and evening. Will
let the next shift issue the advisory after looking at the
incoming suite of 00z models.
Showers will accompany a trough of low pressure Sunday night into
early Monday. Showers will taper off on Monday and become
confined to the west slopes of the mountains and possibly a
convergence zone as onshore flow gradually decreases late in the
day. With the more showery precipitation and some breaks in the
clouds during the afternoon hours, temperatures will be a few
degrees warmer on Monday than on Sunday.
A warm front will brush the area on Tuesday bringing rain to
mainly the olympic peninsula. The northern 2/3 of the interior may
see some rain as well, but amounts in the interior will be quite
light as most energy with the warm front lifts into Vancouver
Island. Tuesday high temperatures will mainly be in the lower to
mid 50s again.
The current short term forecast is in good shape. No update is
Long term...from the previous long term discussion: a frontal
system will move slowly through the area Tuesday and Wednesday.
Tuesday does not look too wet--it is just a brush by warm front
and most of the rain GOES into British Columbia during the day.
That front sags south into western Washington Tuesday evening, and
the rain picks up, and then a surge of heavier rain should arrive
later Tuesday night through Wednesday. The front moves inland
Wednesday night, and then a cool upper trough will move through
the region Thursday with a good chance of the pscz setting up.
Friday looks like it has a good chance to be a dry day under high
pressure, and that might extend into next Saturday as well.
Aviation...weak high pres aloft will prevail over the region
overnight. West flow aloft will become SW overnight. The low level flow
will be light offshore or Ely. Expect VFR conditions overnight.
Ksea...VFR conditions thru Sunday morning. Winds will become light
falling pressure over the offshore waters, ahead of a frontal
system, along with higher pressure inland will result in easterly
flow overnight. Expect the occluded front, currently well offshore,
to move on the Washington coast late Sunday for onshore flow. The next
frontal system is anticipated on Tuesday, followed by another one
Hydrology...river flooding is not expected for the next 7 days
with the exception of possibly the flood prone Skokomish River in
Mason County, where heavier rain in the Olympics Tuesday night
and Wednesday could be enough to get the river above flood stage.
Pz...gale warnings are in effect for much of the coastal waters.
Small craft advisories are in effect for the remaining
waters except the Puget Sound/Hood Canal.