Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 271048
Area Forecast Discussion
National Weather Service Seattle WA
348 AM PDT Mon Mar 27 2017
.SYNOPSIS...An upper level trough will give showers to the area
through tonight. A warm front will move through the area on
Tuesday. A stronger front associated with a vigorous low pressure
system will give rain and windy conditions to the area Tuesday
night and Wednesday. Another upper level trough will give showers
to the area on Thursday. Dry weather is expected on Friday.
.SHORT TERM...Satellite imagery shows upper level trough along the
coast this morning. Plenty of shower activity on the doppler
radars with most of the shower activity west of Puget Sound. Under
cloudy skies temperatures were in the 40s.
Upper level trough moving through the area this morning spreading
showers over the entire area. Satellite imagery shows shower
activity behind the trough axis which will keep showers in the
forecast for this afternoon. High temperatures will continue to be
below normal...in the upper 40s and lower 50s.
Flat upper level ridge moving over western Washington overnight
with a warm front moving over the top of the ridge into Vancouver
Island early Tuesday morning. Shower activity will decrease in
the evening. Rain associated with the warm front spreading over
the northwestern portion of the area late. skies will remain
cloudy with lows in the 40s.
Warm front dropping down over western washington on Tuesday for
another round of rain. Rainfall amounts will not be much, up to a
quarter of an inch in the lowlands. With all the cloud cover
highs will have a tough time getting much warmer than the lower
Rain out ahead of the trailing cold front moving over western
Washington Tuesday night. Rain continuing into Wednesday morning
with a frontal passage late in the morning changing the
precipitation to showers. A few hours of southwesterly 850 mb
winds of 30 to 45 knots along the south slopes of the Olympics
will enhance the rainfall rates considerably in that location
late Tuesday night into Wednesday morning. A weakening 1006 mb low
will move inland over the southern portion of Vancouver island and
into the interior of southern British Columbia Wednesday
afternoon. Surface gradients will increase Wednesday morning with
winds increasing rapidly. There is the potential for the wind
speeds to reach advisory criteria Wednesday afternoon especially
from Everett northward. Lows will again be in the 40s Tuesday
night with highs in the lower to mid 50s on Wednesday.
.LONG TERM...Extended models in good agreement with an upper level
trough moving through western Washington on Thursday keeping
showers in the forecast. Upper level ridge builds behind the
trough Thursday night into Friday with the 500 mb heights rising
into the upper 560 and lower 570 dms. Surface gradients do not
turn offshore but do go northerly during the day. Normal high for
Seattle on Friday 56 degrees. With the sunshine and warming
temperatures aloft will go a couple of degrees above normal with
the warmer locations getting into the lower 60s.
Model inconsistencies continuing for the weekend with the GFS a
little stronger with the upper level ridge weakening the next
front enough to reduce the precipitation significantly. The ECMWF
is weaker with the ridge with the next system relatively intact as
it moves through western Washington on Saturday. Inconsistencies
continue on Sunday with the ECMWF swinging a trough through the
area while the GFS has an upper level low to the south with a
convective southerly flow aloft pattern. Neither model favored at
this point so will stay with the chance pops through the weekend.
.AVIATION...An upper level trof of low pres over the area will move
into ern WA and ID this afternoon. SW flow aloft will become strong
nly this afternoon. A surface trof will move across the area during
the day today. The low level flow remain sly. Expect areas of MVFR
CIGs/VSBYs, especially with the heavier showers. The mtns will be
obscd at times.
KSEA...It looks like CIGs will bounce between VFR and MVFR
categories all day today, continuing thru tonight. Winds will be sly
7-12 kt, possibly gusty (near 20 kt) this afternoon.
A trough over the offshore waters will move across the area today
for continued southerly flow. The flow will back slightly tonight
ahead of a weak cold front. This front will move across the area on
Tuesday. A strong frontal system will impact the region on Wednesday
for gale force winds over parts of the area.
.HYDROLOGY...A wet frontal system will give rain to the area later
Tuesday through Wednesday. While precipitation amounts will only
be moderate, soils are quite saturated and there will be a good
deal of runoff. Most rivers will see rises, and a few could
approach bankfull on Wednesday.
The flood-prone Skokomish River looks like it will go over flood
stage early Wednesday and may see moderate flooding. A Hydrologic
Outlook remains in effect.
With the saturated soils and another round of moderate rain
expected Tuesday night into Wednesday for the lowlands the
landslide threat will be elevated once again. Felton
.CLIMATE...With measurable rain already this morning at Sea-Tac
that makes 45 days with measurable rain since February 1st. Only
two years in over 120 years of weather records in Seattle have
had more rain days in February and March, 1961 with 49 days and
2007 with 46 days.
Through 3 am this morning the combined February and March
precipitation total for Seattle is 15.36 inches. This is the
second highest total on record. The record is 15.55 inches set in
There has been measurable precipitation on 23 out of the 27 days
at Sea-Tac this month. The record for the most days with
measurable precipitation in March in Seattle is 27 days in 1989.
There has been measurable rain every day so far this month at
Quillayute. The current rain day streak including this morning is
35 days in a row. The record is 47 days in 1990. Felton
PZ...Small Craft Advisory for hazardous seas until 6 PM PDT this
evening for Coastal Waters From Cape Flattery To James
Island 10 To 60 Nm-Coastal Waters From James Island To
Point Grenville 10 To 60 Nm-Coastal Waters From Point
Grenville To Cape Shoalwater 10 To 60 Nm.
You can see an illustrated version of this discussion at