Scientific Forecaster Discussion
fxus66 ksew 171022
Area forecast discussion
National Weather Service Seattle Washington
322 am PDT Mon Jun 17 2019
Synopsis...areas of marine layer clouds will spread inland again
this morning. Tuesday will see more moisture and perhaps a little
morning drizzle or a few showers. An upper trough will move through
the region Wednesday and Thursday. Weak high pressure might build
toward the end of the week before an upper low arrives Sunday.
Short term /today through Wednesday/...the marine layer morning
clouds have been burning off from the interior of western Washington
these past few days--and that's a good bet again today. However,
Tuesday will see a deeper marine layer (and the tail end of a
weather system that will be moving into British columbia) and some
morning drizzle or shower activity will develop. Wednesday will see
temps continue to cool as an upper trough begins to sag over the
area and a few light showers or morning drizzle is again possible.
It is Worth noting that a 300mb 130-150kt jetstream will sag south
over the area from Tuesday night through Wednesday night and that
700mb winds peak at 40-50kt early Wednesday morning (not that many
people climb above 700mb...but they do on mount rainier) ... of
course there will be plenty of low level onshore flow as well.
Long term /Thursday through Sunday/...the chance of showers will
continue through Thursday--and the sharpest shortwave upper trough
arrives on Thursday, so that day could see heavier scattered showers
develop. The GFS now shows a little brief ridging toward the end of
the week, and then an upper low arrives on Sunday. So, we might see
a little more sunshine Friday and Saturday and then go back into
clouds and showers on Sunday. The European model (ecmwf) is similar, but with 500mb
heights only rising to about 573dm, perhaps the most we can expect
is for marine layer clouds to break up a little faster in the
afternoons--and just for a day or two. It is interesting to note
that 500mb heights are 100m higher today then they are forecast to
be under that weak ridging late in the week, so today might very
well be the last warmish day for awhile.
Aviation...weak upper level ridge moving through the area today
with another weak shortwave moving by to the north tonight.
Westerly flow aloft. In the lower levels onshore flow will continue
Stratus already down the Strait into Whidbey Island in the north and
moving into the southern Puget Sound area to the south. By 14z most
of The Lowlands will be covered by stratus with ceilings below 1000
feet and isolated visibility 1-3sm in fog. Ceilings lifting to 1000-
2000 feet late morning with the stratus retreating back to the
coast in the early to mid afternoon hours. Increasing onshore flow
overnight will drive the stratus back over the interior by 12z
Tuesday with ceilings 1000-2000 feet.
Ksea...ceilings lowering down to below 1000 feet 12z-14z.
Ceilings lifting to 1000-1500 feet 17z-19z with the clouds
scattering out around 21z. Stratus returning to the terminal
after midnight. Southwest wind 4 to 8 knots trying to go
northwesterly this afternoon but ending up in the 270-300 degree
Marine...high pressure over the coastal waters with lower
pressure inland will result in varying degrees of onshore flow
through the week. Gale force westerlies in the central
and eastern Strait of Juan de Fuca late afternoon and evening hours
today and again on Tuesday with small craft westerlies in the
morning and most of the afternoon hours. Small Craft
Advisory winds in the adjacent waters, Admiralty Inlet and northern
inland waters in the evening hours the next couple of days as well.
Onshore flow continuing through the week with Small Craft Advisory
winds in the central and eastern Strait each evening Wednesday
through Friday. Felton
Hydrology...the daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
Pz...Small Craft Advisory until 5 PM PDT this afternoon for central
U.S. Waters Strait of Juan de Fuca-East Entrance U.S.
Waters Strait of Juan de Fuca.
Gale Warning from 5 PM this afternoon to 5 am PDT Tuesday for
central U.S. Waters Strait of Juan de Fuca-East Entrance
U.S. Waters Strait of Juan de Fuca.
Small Craft Advisory from 6 PM this evening to 5 am PDT Tuesday
for Admiralty Inlet-northern inland waters including the
San Juan Islands.