FXUS66 KSEW 262139
Area Forecast Discussion
National Weather Service Seattle WA
240 PM PDT Sun Mar 26 2017
.SYNOPSIS...A front will move inland this evening with rain
turning to scattered showers. A trough will keep showers in
the forecast Monday. A warm front will reach the area Tuesday
for more rain. A vigorous low pressure system and front will
move through the area on Wednesday. A trough will keep showers
in the forecast Thursday. Dry weather is expected Friday.
.SHORT TERM...Rain from a front will break up to showers tonight
and the showers should become more scattered on Monday. The winter
weather advisory for portions of the Cascades has been cancelled,
snowfall tonight will be between 2 and 5 inches above the snow
level, unremarkable. Tuesday will see a warm front arrive and that
system fizzles out over the area Tuesday evening. Another frontal
wave, this time a stronger system, will move through Western
Washington on Wednesday. The 12z GFS took a deepening 999mb low
into Vancouver Island midday, with a decent southerly gradient
giving windy conditions over the area.
.LONG TERM...The push of onshore blustery weather behind the system
on Wednesday will settle down Wednesday night and Thursday. An upper
trough moves inland and surface high pressure builds across
the region. An upper ridge will be in place Friday for a dry day
with some sunshine. Clouds will likely increase Friday night with
a chance of rain by Saturday as a warm front pushes into the ridge.
.AVIATION...An upper level trough off the coast is forecast to move
onshore into Western Washington Monday. SW flow aloft over
Washington tonight becoming NW behind the trough. At the surface, a
frontal system was moving onshore this afternoon and will continue
inland this evening. Onshore flow behind the front. Air mass
becoming somewhat unstable behind the front for showers into Monday.
MVFR ceilings in the vicinity of the front. Showers with a mix of
breaks in the cloud cover tonight into Monday morning will offer a
mix of MVFR and VFR conditions. Mountains to remain obscured in
clouds and precipitation through at least Monday morning.
KSEA...The terminal is likely to have primarily upper end of MVFR
ceilings both with the front late this afternoon and evening, and
through the night into Monday morning with passing showers and cloud
cover. Improving VFR conditions likely Monday afternoon. Southerly
winds around 10 kt should kick in with the front and continue
through Monday morning. Buehner
.MARINE...An occluded front was moving onshore this afternoon
and will continue inland tonight. Low level onshore flow with and in
the wake of the front. Will change the gale warnings to small craft
advisories that will only last until this evening.
A surface trough is expected to move onshore Monday with a showery
weather regime and then higher pres building behind it Monday night.
The next weak Pacific frontal system is expected to arrive Tuesday.
A low is expected to develop and intensify as it tracks from well
off Cape Blanco northeast into central Vancouver island Wednesday
with potential gale force winds at least for the coast. The
associated cold front to move onshore late Wednesday with moderate
onshore flow. Higher pres to build onshore Thursday into Friday.
.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...Small craft advisory near shore coast, Strait of Juan de Fuca,
Northern Inland Waters and Admiralty Inlet until this evening.
You can see an illustrated version of this discussion at
Humidity Humidity is the amount of water vapor in the air. The term "humidity" refers to relative humidity. Relative humidity is defined as the amount of water vapor in a sample of air compared to the maximum amount of water vapor the air can hold at any specific temperature in a form of 0 to 100%. Relative humidity is important in forecasting weather. Humidity indicates the likelihood of precipitation, dew, or fog. High humidity makes people feel hotter outside in the summer because it reduces the effectiveness of sweating to cool the body by preventing the evaporation of perspiration from the skin.
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