Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
349 am PDT Tue Oct 25 2016
a series of low pressure systems will lift north along the Pacific
coast over the next several days. This will keep the area in a
generally unsettled and wet pattern with temperatures near or
slightly above normal.
a surface low pressure system currently centered near 50n/130w is
well evident on satellite imagery. The low will meander around in
the same general vicinity today, while slowly weakening. Tightest
pressure gradients will remain off the coast and leave strong
winds out over the coastal waters only. Winds this morning
offshore have ranged from peak gusts of 30-45 knots. Scattered
showers will linger across the area today as the low remains well
west. Highest pops will exist west of Puget Sound. The low will
steadily weaken and lift northwest providing and drier day on
Tuesday. However overnight another surface low pressure system
will lift north roughly along 130w. Noting a better shot at more
widespread and heavier rainfall with this Wednesday system.
Isentropic lift present with a northward moving moisture advection
Wednesday. A quick glance at naefs means depicts that the narrow
push of 1 to 1.25" precipitable water 12-18z wednesdays is 90th
percentile with respect to climatology. As is the ivt across the
southern half of the forecast area at that time. So this would
suggest potential for some heavier downpours as the rain lifts
north through the area Wednesday 12-18z. This will mean some
commute imapcts that morning for Seattle Metro area with possible
downpours. The strong ivt and enhanced plume of precipitable water will exit the
area as the surface low rotates north quickly by Thursday.
Temperatures in the short term period will be above normal.
the general idea of northward progressing surface features
continues through the weekend and into early next week. The GFS
and Euro are in good agreement on this and the general 500 mb
pattern. This agreement holds through Monday. Both models show a
500 mb trough sliding through the area, with the GFS being deeper
and slower with the feature. For now will just continue the
ongoing inclusion of pops through all periods in the forecast. The
progression of weak surface lows and occasional increase in shower
chances as they draw in moist air from the south will continue.
However none of these low pressures look remarkable in terms of
strength or impacts. Pressure gradients remain weak as the lows
aren't strong, so winds not expected to be significant except over
the coastal waters. Rain amounts will steadily add up but over a
several day period. Amounts of 1-3 inches from now through next
Monday will be spread across several days to minimize impacts. The
general theme is temperatures near to above normal with chances
of rain every day for the next week. Look for many areas to close
out with a top 3 wettest October on record across western
Aviation...large upper level low west of Vancouver Island
slowly moving north and weakening through tonight. Warm
front moving up from the south reaching western Washington early
Wednesday morning. Moist southwesterly flow aloft with mid/high
level moisture. Drier easterly flow at the lower levels.
Ksea...mid and high clouds today and tonight. Ceilings lowering into
the 3500-5000 foot range Wednesday morning with the onset of rain.
Southeast wind 5 to 10 kt becoming southerly 10 to 15 knots later
this morning into the afternoon hours. Wind switching to
northeasterly tonight. Felton
Marine...a 975 mb low about 3000 miles northwest of Cape
Flattery will continue to weaken and move toward haida gwaii today
and tonight. Gale force winds over the coastal waters, entrances to
the Strait, and northern inland waters wil ease this afternoon.
A second low - near 995 mb - will track northward inside 130w late
Wednesday afternoon into Wednesday night. There is the potential for
another round of gales with this low Wednesday and Wednesday night
along the coast.
Low level flow will turn offshore on Thursday and remain
light offshore on Friday. Felton
Pz...Gale Warning until noon PDT today for coastal waters from Cape
Flattery to James Island 10 to 60 nm-coastal waters from
Cape Flattery to James Island out 10 nm-coastal waters from
James Island to Point Grenville 10 to 60 nm-coastal waters
from James Island to Point Grenville out 10 nm-coastal
waters from Point Grenville to Cape Shoalwater 10 to 60 nm-
coastal waters from Point Grenville to Cape Shoalwater out
10 nm-West Entrance U.S. Waters Strait of Juan de Fuca.
Small Craft Advisory for rough bar until 5 am PDT Wednesday for
Grays Harbor bar.
Gale Warning until 3 PM PDT this afternoon for East Entrance
U.S. Waters Strait of Juan de Fuca-northern inland waters
including the San Juan Islands.
Small Craft Advisory until 6 PM PDT this evening for Admiralty
You can see an illustrated version of this discussion at