Scientific Forecaster Discussion
fxus66 ksew 192213
Area forecast discussion
National Weather Service Seattle Washington
213 PM PST Tue Nov 19 2019
in the wake of a departing low pressure tonight, high pressure
will build in for mid- late week. With the high building in,
sunnier and drier weather is expected. This will be accompanied by
near normal temperatures and morning fog. It will remain dry
until Saturday night and Sunday when low pressure will approach
from the north and bring clouds and rain. This will bring the
start of a more active weather pattern next week with increased
Short term /tonight through Friday/...
current radar shows that showers have ended across the area.
Clouds have been steadily eroding as well, with the cloudiest
skies found east and south of the sound. Northerly breezes will
diminish overnight, and skies will clear, allowing for the
formation of some fog overnight with low temperatures cooling into
the 30s to low 40s for most areas. Wednesday will begin a stretch
of several days of high pressure dominated weather. This will
bring mainly sunny skies and temperatures close to normal. This
will mean highs in the upper 40s to low 50s with nighttime lows
ranging from the mid and upper 20s in the cold spots, to low to
mid 30s in the urban areas. With clear skies, morning fog is also
expected, especially in favored locales like low lying areas and
Long term /Saturday through Tuesday/...
by the weekend, change will be afoot in the form of an approaching
low pressure system to the northwest of the area. A careful
consideration to current deterministic runs indicates some timing
differences between the major global models. Through an ensemble
perspective, mean values of quantitative precipitation forecast suggest that rain will begin
across the area Saturday evening and overnight into Sunday
morning. That leaves Saturday as a day with increasing clouds, but
primarily dry through the daylight hours for most of the region.
Rain will increase across the area through Sunday and rain will
continue off and on for several days. The ensemble quantitative precipitation forecast plumes do
not depict a significant amount of rain however on the weekend to
early next week system. Monday will be a more showery day with
cooler temperatures and falling snow levels. Snow levels will dip
to pass level late Sunday.
Right at the end of the 7 day period, Monday night and into
Tuesday, there is the approach of a second system, which is
presently stronger on the European model (ecmwf) than GFS solutions at that time
period. However both do show a stronger and colder storm system
across the area around day 7. This will bear watching for future
trends. Nonetheless, even the currently stronger European model (ecmwf) solution
takes the surface low on a more northerly track.
Aviation...clearing will work south through western Washington this evening.
The flow aloft is northerly. The air is stable. Sunny weather is
on tap for Wednesday except for some patches of morning fog.
Ksea...skies will clear this evening in the northerly breeze.
Marine...pressure gradients haven't done much as high pressure builds in behind the
low pressure system departing. There are decent northwest winds in the
outer coastal waters, but those will decrease overnight. The
northerly should become a little stronger across the inland waters
tonight. Light offshore flow will prevail for the remainder of
the work week before the next system arrives Saturday night.
Hydrology...river flooding not expected for the next 7 days.
Pz...Small Craft Advisory until 2 am PST Wednesday 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.
Small Craft Advisory for rough bar until 4 am PST Wednesday for
Grays Harbor bar.
Small Craft Advisory until 2 am PST Wednesday for East Entrance
U.S. Waters Strait of Juan de Fuca.
Small Craft Advisory until 9 am PST Wednesday for northern
inland waters including the San Juan Islands.