Area forecast discussion
National Weather Service Portland or
150 PM PDT Wednesday may 22 2013
Synopsis...a cold upper low will remain anchored over the
Pacific northwest for the remainder of the week...keeping a cool showery
weather pattern in place for the next few days. The low will weaken
over the weekend...reducing the chances for showers...and allowing
temperatures to warm back closer to normal.
&&
Short term...upper low was seen in satellite pictures over
southcentral Washington this afternoon...with widespread rain and imbedded
showers over the forecast area. A layer of moist isentropic lift was
seen in models between 285 and 290k...coincident with the main area
of rain. Models suggest the isentropics weaken this afternoon and
evening...but with the upper low remaining over Washington overnight...will
leave probability of precipitation high through most of the night. Focus for best
precipitation chances shifts to the northwest part of the area Thursday as the
main lobe rotating around the low moves S over the Washington coastal
waters...then inland over Oregon Thursday night. After a day of what will
likely be record cool today...temperatures should be a bit warmer
Thursday due to warming of the low and a lack of persistent rain.
By Friday models agree the center of the low should begin drifting NE
of the region as the main shortwave moves east around the base of the
low. While models suggest some weaker shortwaves digging down the
back of the main trough...expect to see a decrease in rain chances
Friday into Sat. Expect to see gradually warming temperatures Friday and Sat as
the upper flow becomes more westerly.
Long term...Saturday evening through Tuesday...several shortwave
systems rotate through a broad upper level low over the northeast
Pacific and West Coast. The upper low lingers across the region
through the weekend...keeping periods of showers and brief cloud
breaks in the forecast through the weekend. The models show more
organized systems arriving along the West Coast early next week with
a change from intermittent showers to steady rain likely during the
beginning of next week. Snow levels rise slightly early next week
with temepratures still remaining slightly below normal. There is
still no tendency in the long range forecast for ridging to return
to the northwest. Kwelson
&&
Aviation...upper low over region will move little tonight. Current
mix of MVFR and VFR...with the worst over the interior north of ksle.
Little change this evening...with steady light rain and MVFR
conditions. Higher Cascades and passes obscured in clouds and light
snow. Precipitation becoming more showery after 05z... with mostly low VFR
and high end MVFR ceilings.
Kpdx and approaches...MVFR ceilings and steady rain through 06z then
gradual change over to showers occasional light rain. Ceilings remain
MVFR at 1500 to 2000 feet through 06z...then slight improvement but
still high MVFR. Looks like low VFR ceilings after 18z Thursday. Rockey.
&&
Marine...little change. West to northwest winds continue...generally 10 to
15 knots....but 15 to 25 knots over the far outer waters this evening.
Winds ease tonight as gradients relax. Winds remain 15 knots or less
through sun as pressure gradients not all that strong. Another front
will arrive early next week...with S to SW winds up to 20 knots again.
Seas generally 10 to 13 feet tonight...but will gradually subside
later tonight and Thursday...dropping below 10 feet late tonight. Seas
will continue to gradually subside through sun. Rockey.
&&
Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...Small Craft Advisory for winds until 6 PM this evening for
the outer waters...or 10 to 60 nm offshore.
Small Craft Advisory for hazardous seas this evening for
all coastal waters.
Small Craft Advisory for rough Columbia bar conditions tonight.
&&
$$
More weather information online at...
http://weather.Gov/Portland
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.
