Scientific Forecaster Discussion
fxus66 ksew 211012
Area forecast discussion
National Weather Service Seattle Washington
313 am PDT Sat Sep 21 2019
Synopsis...high pressure will keep conditions dry and warm today
although some clouds will be present. A cold front will spread rain
through the area on Sunday. Wet and showery weather will continue
through early next week with temperatures trending below normal.
Short term /today through Monday/...current infrared satellite shows
fairly clear in the mid and upper levels while switching to lower
levels the beginnings of some fog development can be seen...mainly
within the more prone areas of the County Warning Area.
As one would expect from such conditions...an upper level ridge is
in place over West Washington this morning and will weaken as well as move
eastward throughout the day today. This will bring about the warmest
temperatures of the forecast period with most lowland locations
reaching highs in the mid to upper 60s...with maybe an isolated 70
here or there.
An approaching cold front tonight will kick off a
period of active weather...both in the short and long term. This
feature will make it to the coast late tonight but will not begin
its inland push until early Sunday morning. Rain will be the order
of the day for the most part with a transition to showers expected
in the afternoon as the front slowly moves away. A brief break in
the action is expected during the overnight hours Sunday night into
early Monday morning...but a system passing just to the north will
have enough moisture sag down over the Canadian border to keep pops
in the forecast for north of Seattle most of the day before a
southward push will spread the chance of rain over the entire County Warning Area
Monday night. Temps in The Lowlands during this period will cool
with afternoon highs Sunday in the lower to mid 60s and ranging in
the upper 50s to mid 60s Monday. Smr
Long term /Tuesday through Friday/...there are hints at a break in
the action Tuesday as a large scale trough shifts more toward the
center of the US...the European model (ecmwf) showing this a bit better than the
current GFS...but models come back in agreement that another large
scale trough will begin to set up shop over the area starting
Wednesday night with a series of upper level lows dipping down into
the area and making for a generally wet remainder of the week.
Models do disagree on timings and paths of these lows however...so a
break or two in the action is certainly possible. For example...the
GFS tries to push an upper level low south of the area to the California/or
border Friday which would make for a potentially dry day...but the
European model (ecmwf) keeps the system further north close to the Washington/or border which
would keep the potential for rain going. Opting to split the
difference and thus advertise a generally wet pattern until a more
Concrete consensus emerges. Temps will continue their cooling trend
through this period. Lowland highs will start off Tuesday in the
lower to mid 60s but fall into the mid to upper 50s Thursday which
is cooler than what would normally be seen this time of year. Smr
Aviation...northerly flow aloft will transition more westerly to
southwesterly today as an upper level ridge slides over the area.
Patchy stratus over West Washington at this hour with areas of LIFR over the
sound and MVFR/IFR across portions of the interior. Some VFR will
become MVFR/IFR this morning as stratus is expected to become more
widespread. Fog at kpwt into the morning with fog possible at kolm.
Cigs will transition to VFR by early afternoon as stratus clears.
The next frontal system will approach the area later today through
tonight with the next chance for rain and lower ceilings. Winds
generally southerly through today 4 to 8 knots. Jd
Ksea...IFR cigs at this hour with MVFR/IFR through the morning.
Stratus will clear by midday and improve to VFR for the afternoon.
Winds southerly 4 to 8 knots. Jd
Marine...lighter onshore flow through today. A frontal system will
move through the area late tonight through Sunday. Small Craft
Advisory issued for the coastal waters with increased southerlies
ahead of the front tonight into early Sunday. Small craft westerlies
following the frontal for the coastal waters through Sunday night
with Small Craft Advisory level winds possible in the central and eastern portions of
the Strait of Juan de Fuca Sunday night. Another front will slide
through Monday into Monday night across the area. Jd
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 from 2 am Sunday to 2 am PDT Monday 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.
Small Craft Advisory from 2 am to 8 am PDT Sunday for coastal
waters from Cape Flattery to James Island out 10 nm-coastal
waters from James Island to Point Grenville out 10 nm-
coastal waters from Point Grenville to Cape Shoalwater out