Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
225 am PST sun Mar 1 2015
Synopsis...an upper ridge with its axis out near 140w will be the
dominant feature this week...producing northerly flow aloft across
the Pacific northwest. A weak disturbance will move south in this
flow today with mainly a few high clouds. A more substantial
disturbance will move south along the Pacific northwest coast
tonight. Its track will give the best chance of precipitation to the
coastal waters and the coastal areas tonight. Clouds will decrease
and showers dramatically decrease Monday as the system moves south.
Then it looks pretty dry through the remainder of the week. A weak
system is forecast to ride over the ridge and move off to the east
around Thursday. The main effect at this point will be to turn the
low level flow onshore and perhaps give a few clouds to the area. Any
precipitation from this system is looking pretty iffy.
Short term...the breezy offshore flow of Saturday was decreasing
this morning as the northeast flow aloft on the north side of an
upper low in California continued to move away. This offshore flow
lowered dewpoints across the area...and has allowed temperatures to fall
close to freezing in much of the area.
Otherwise...the dominant feature affecting the Pacific northwest this
week will be an upper ridge with its axis out near 140w. This is
producing a northerly flow aloft across the Pacific northwest.
A weak short wave will move south through the Pacific northwest today
with mainly some higher clouds. A more substantial short wave will
drop south along the b.C. Coast today and move south along the
Washington and Oregon coasts tonight. The track will give the best
chance of rain to the coastal waters and the coastal areas...with
decreasing chances inland. This system will have some colder air with
it for some snow in the mountains and possibly the foothills and
Coast Range...but amounts will be pretty light as you go eastward and
impacts will be limited.
The system moves south of the area pretty early Monday for
dramatically decreasing showers and for decreasing clouds. It then
looks dry into the middle week period with mainly a few higher clouds at
times as another weak upper disturbance or two moves through.
Long term...no changes. Previous discussion follows...
Tuesday night through Saturday...extended forecast models continue to
show March coming in like a Lamb for the Pacific northwest. The mean
upper ridge position lingers where it has been much of this
winter...over the NE Pacific and along the West Coast. This should
keep the Pacific jet stream well to our north...as well as any
chances of significant precipitation. Removed mention of any rain
from the forecast Tuesday through Saturday. Conditions may become
increasingly favorable for fog in the valleys...as most guidance
pushes the upper ridge axis onshore late in the week. Otherwise
expect a gradual return to above normal temperatures which may last
into next weekend. Weagle
Aviation...light offshore wind with VFR this morning. Will have
pockets of fog...mainly in Cowlitz valley and coastal areas. Weak
front approaching from the northwest will bring increasing clouds this
afternoon. Will remain VFR...but ceilings will lower to MVFR after 02z
along the coast...and inland after 05z. Ceilings will remain low tonight
with occasional light rain and obscured higher terrain.
Kpdx and approaches...VFR conditions today...with increasing middle and
high clouds this afternoon. Will see increasing MVFR ceilings after 05z
as front approaches from northwest. Rockey.
Marine...high pressure over the NE Pacific will be the dominant weather
player this week. However...a weak front will drop southward across
region tonight into Monday am. Not a lot of wind expected with
front...but enough to pop 20 to 25 knots gusts over the outer
waters...mainly off central Oregon coast. Will maintain Small Craft
Advisory for that area. Seas mostly holding at 4 to 6 feet.
Another weak front may push into the waters Thursday and possibly again
next weekend...but winds will remain under 20 knots. Rockey.
Pz...Small Craft Advisory for winds for late tonight to Monday am
on outer coastal waters between Cascade Head and Florence.
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This discussion is for northwest Oregon and southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area.