Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
345 am PST sun Feb 1 2015
Synopsis...a weak cold front will move through today for rain at
times...followed by another weak front Monday. Some light showers
will linger Tuesday and Wednesday. A transition to a fairly wet and
mild pattern will begin Thursday and continue through next weekend.
Short term...satellite imagery shows weak warm front over southern
British Columbia extending down into the north Cascades with a weak
cold front offshore near 130w at 11z/3am. Plenty of cloud cover over
western Washington with patchy fog mainly from about Tacoma south to
Chehalis. Temperatures with the cloud cover were in a narrow
range...upper 30s to middle 40s.
Warm front will continue to move east this morning with the total
precipitation in the north Cascades with the front around a tenth of
an inch. Cold front off the coast reaching the coast around
21z...interior around 00z moving into the Cascades late
afternoon/early evening hours. The front is not very organized with
the cloud top temperatures with the front slightly warming in the
last few hours. Still even with the weakness of the front expect a
few hundredths of rain across the area today. Will stay with the
high pop low quantitative precipitation forecast scenario with rain at times wording. High will be
near normal...around 50 degrees.
Not a lot of cold air behind the front this evening with most of the
limited Post frontal shower activity confined to the Cascades by
06z. Lows temperatures Monday morning will be in the upper 30s to
Another weak and diffuse front will reach western Washington late
Monday with the rain out ahead of the front spreading across the
area during the day. This system is in the development stage right
now near 140w. By Monday morning the models show the front to have
some negative tilt to it. This will slow down the eastward progress
a touch. With the front approaching from the southwest and slowing
down have scaled back the probability of precipitation over the northwest interior to chance
for Monday morning. This system will be a little wetter than todays
with up to a half inch of rain in The Lowlands with up to an inch of
water in the mountains. Snow levels will be near 4000 feet.
Western Washington in a bit of a lull later Monday night and Tuesday
with westerly flow aloft over the area. Front east of the Cascades
by 06z Tuesday. Models have been having a hard time latching on to a
solution for Tuesday. The 00z GFS and European model (ecmwf) bring a warm front into
Oregon on Tuesday leaving western Washington with light western
flow aloft and light surface gradients. Will keep a chance of
showers in the forecast with the warm front in the vicinity and
moist westerly flow aloft.
Long term...model solutions for Wednesday continue to show a lack
of consistency among the models. The European model (ecmwf) has a warm front over
Oregon trying to lift north into western Washington. The GFS has a
weak shortwave riding by to the north of the area. GFS ensembles
show little variation in their solution on Wednesday which lends
some confidence to the GFS solution but with the lack of model
consensus will keep the chance probability of precipitation in the forecast. While there are
some differences in the timing of the systems beginning Thursday
the extended models are in much better agreement in regard to the
overall pattern turning warmer and wetter beginning Thursday and
continuing through next weekend. Timing of the individual features
is tough at this point so a broad brush rain likely/rain at times
forecast looks god Thursday through Saturday. Felton
Hydrology...flooding is not expected through at least Thursday.
A series of systems moving through the area Thursday night through
Saturday will cause rivers to rise but with a few breaks in the
steady precipitation the only threat of flooding in this scenario
looks to be on the Skokomish River next weekend. Felton
Aviation...a weakening upper trough and front will move through
western Washington today. Westerly flow aloft. Low level offshore flow will
become southerly today. The air will be moist and stable as areas of rain
spread into western Washington and the mountains will become obscured.
Ksea...ceilings should drop with rain at times today and the stable air
and light winds this morning may end up giving some lower visibility at
times...3-5sm -ra br seems likely at times today. Taf looks fine
there with a southerly breeze developing with the front by 18z...although
it is still calm at 2am.
Marine...offshore flow early this morning will turn southerly by
middle morning as a weak front reaches western Washington. A little stronger front
will reach the area on Monday. A few areas will have Small Craft
Advisory winds with these two systems. Weak high pressure should be over
the area Tuesday...and then another weak system will reach the area
Wednesday. Around next Thursday there is a chance for more vigorous fronts with
deep low pressure near 140w.
Pz...small craft advisories are in effect for the coastal waters
from Cape Flattery to James Island out to 60 nm and the west
West Entrance to the Strait of Juan Delaware fuca.
You can see an illustrated version of this forecast discussion at