Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Seattle Washington
345 am PST sun Nov 29 2015
Synopsis...high pressure aloft will remain over the region
through tonight. A strong temperature inversion will also remain
in place through Monday morning for below normal temperatures
across much of the lowland interior. A weak low pressure system
will bring light precipitation to the area on Monday. A stronger
system will impact the region on Tuesday.
the Pacific northwest will remain under the influence of an Omega
block for another day. The blocking high will slowly shift east
tonight through Monday...thereby allowing a weakening low pressure
system to approach the region. Slowed down the timing of the
precipitation slightly or until during the day Monday due to the stubborn
block. Would not be surprised if precipitation is delayed further. At
any rate...much of the interior will likely remain dry on Monday.
A strong inversion will remain in place over the interior lowlands
through at least Monday morning. This will result in continued below
normal temperatures over much of the lowland interior...especially from
the south Puget Sound sound region southward. In contrast...temperatures over
the the coast and mountains /not prone to cold easterly flow/
will be above normal. Keeping the air stagnation advisory going
through noon Monday looks good since not much mixing is expected to
take place until Monday afternoon. If the system is delayed further...
the advisory may need to be extended.
A stronger low pressure system is expected to impact the region
on Tuesday for locally heavy precipitation along with gusty winds Tuesday night.
At this time...it appeared that speeds will stay below high wind
criterion. The coast and parts of the northwest interior will
likely experience speeds meeting Wind Advisory criterion Tuesday
no major changes to the previous thinking. A series of Pacific
storms will keep this period quite active. It looks like there
will be windy conditions on Wednesday...with speeds possibly reaching
advisory criterion over the coast and northwest interior.
Aviation...the strong upper level ridge over the Pacific northwest
will drift slowly east through Sunday night. A weak surface ridge
over southern British Columbia and eastern Washington will maintain
dry low level offshore flow. A very strong inversion is in place
over western Washington making the air mass very stable.
Areas of LIFR fog and stratus have formed. The areas with the most
fog are over the southern greater Puget Sound sound...the southwest
interior...and along the Strait of Juan Delaware fuca. River valleys also
probably have fog. Fog coverage will likely expand this
morning and be more persistent. Most areas should by clear by 21z
but some fog prone areas will stay foggy all day. Early morning
temperatures are nearly all below freezing so freezing fog is likely.
Ksea...visibility to 1/2sm is expected and 1/4sm visibility is
likely at times. The fog could persist until 20z or so. Surface
winds will be calm this morning becoming southerly 4-6 knots in the
Marine...a weak front will approach the region today and shift winds
to southerly. Small Craft Advisory strength winds ahead of the front
are likely on the coast today. The front will move inland on Monday
and dissipate with borderline advisory level winds possible over the
north interior waters.
A stronger front will reach the area on Tuesday. Gales are likely
with this system. The GFS European model (ecmwf) and Canadian models agree that the
rest of the week will be an active weather with gales possible at
times. However confidence in the details is low.
The current period of King tides will have the highest tides this
year. Fortunately strong high pressure over the area this weekend
and light winds appear likely to keep the tidal anomalies minimal.
No coastal flooding is forecast during the high tides. Chb
there is a possibility of minor flooding on the Skokomish River
on Thursday. Rainfall amounts of 3 to 5 inches were being forecast for
the skokomish basin during the 36-hour period ending 4 PM PST Thursday.
Elsewhere...flooding is not expected the next seven days.
Washington...air stagnation advisory remains in effect until noon Monday
for the interior lowlands.
Pz...small craft advisories are in effect for the coastal waters
and West Entrance to the Strait of Juan Delaware fuca.
Gale watches are in effect from Monday afternoon through
Tuesday evening for the coastal waters.
An illustrated version of this forecast discussion can be seen at