Scientific Forecaster Discussion
fxus66 ksew 231804
Area forecast discussion
National Weather Service Seattle Washington
900 am PST Monday Jan 23 2017
Synopsis...an upper ridge will result in generally dry weather
this week. A weak weather system could bring spotty light rain
Wednesday or Thursday.
Short term...low pressure off the Oregon coast (pic0) this morning
will continue diving southward through the day. Some middle level
clouds are lifting northeast, mainly over the Cascades (pic1). A few
showers are possible over higher terrain but most the area will stay
dry today with periods of sunshine. Temperatures are still near
freezing with patchy fog in prone low lying valleys, but any low
level fog/clouds should lift by midday with highs reaching close to
average in the middle 40s.
High pressure building aloft over the region will maintain dry
weather across western Washington Tuesday (pic2) and part of
Wednesday. Temperatures will run slightly below average due to
radiational nighttime cooling and light flow during the day. Cold
pocket locations will likely start off with fog or freezing fog
during the mornings which will clear out in the afternoon. Tuesday
looks to be the sunnier day with some middle clouds on Wednesday.
Models show a weak trough splitting as it approaches the Pacific northwest on
Wednesday. A few showers cannot be ruled out but most likely, the
system will split with moist light precipitation heading into Oregon
or northern California.
Long term...from previous discussion...a very weak front will
dissipate over the region on Thursday. A chance of showers cannot be
ruled out but it is not out of the question that it will simply be a
dry day with decreasing clouds.
An upper ridge will be over the area Friday and Saturday with the
storm track focused on southern British Columbia. A warm front in
the southwest flow aloft will brush the area Friday for a chance
of rain at the coast and perhaps far north interior. A frontal
system will bring a rain threat to all areas on Sunday. Schneider
Aviation...an upper level low (pic10) will remain offshore today
then shift south toward northern California tonight. Light flow aloft,
becoming northerly tonight. The air mass is dry and stable. Ceilings are
mainly VFR aside from patchy low clouds and fog in the south sound.
Ksea...a mix of middle/high clouds today for VFR conditions. Light north
winds at the surface, becoming east/NE tonight. Patchy low clouds
may form after 06z tonight. 33
Marine...northerly flow will prevail across western Washington
today as a 990 mb low (pic11) shifts south and weakens off the
Oregon coast. Meanwhile, seas are still at 10-13 feet and a Small
Craft Advisory for hazardous seas remains in effect. Seas will
subside under 10 feet late tonight. High pressure will bring
generally light winds to the area Tuesday through Thursday. A warm
front will clip the coastal waters on Friday. 33
Hydrology...river flooding is not expected for the next 7 days.
Pz...Small Craft Advisory for hazardous seas until 4 am PST Tuesday
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 Tuesday for
Grays Harbor bar.