Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Portland or
247 am PDT Monday Jul 28 2014
Updated aviation section
Synopsis...an upper level ridge will be centered inland over the
Pacific northwest through the coming week with an upper low centered
off the b.C. Coast. This will bring warm and dry weather to
southwest Washington and northwest Oregon...except for a slight
chance for thunderstorms in the Cascades near the crest in the
afternoons and early evenings as a few weak disturbances lift
northeast through the region through the upcoming week. The marine
layer will be shallow and mostly confined to the coast.
Short term...an upper low off the b.C. Coast and an upper level
ridge anchored inland over the western U.S. Will be the weather
pattern that will affect the Pacific northwest and southwest
Washington and northwest Oregon through this week. This will produce
light south to southwest flow aloft with high 500 mb heights...whose
associated subsidence will allow a shallow marine layer at most along
The air mass today will be a little warmer as 500 mb height and 850
mb temperatures are a little higher. Also less cloud cover is expected
today.Shallow marine layer continues on the coast with low stratus
developing nearshore with minimal clouds overland...but still could
see patches of fog for the coastal lowlands this morning.
There is not really much forcing for thunderstorms today. Moisture is
lacking for much activity except maybe for the high Oregon Cascades.
Moisture will again be high based and sparse...so any thunderstorms
that do develop will be dry.
The same pattern continues on Tuesday. Temperatures inland will be ub the
lower 90s. The models show another weak disturbance lifting north
Tuesday afternoon and evening...so this looks like a better chance of
thunderstorms in the Cascades than on today. Moisture values are
modeled just around 1 inch of precipitable water and it will be at a
more favorable level near 850 mb. So again the high terrain of the
Oregon Cascades will aid in providing a trigger. There is some
threat lingering after midnight Tuesday night. Another shortwave
arrives overnight and lingering moisture may provide enough fuel for
Wednesday looks very similar to Tuesday with a chance of
thunderstorms again over the Cascades in the afternoon and evening.
It appears that on Wednesday thunderstorms may again stay south of
the Columbia River again. The models imply the marine layer may
become more solid along the coast Wednesday...but still not much
expected inland. Temperatures inland will continue to be very warm
Wednesday...up around 90. Tolleson
Long term...Wednesday night through Sunday...models are in agreement
that the upper-level ridge positioned over western U.S. Will remain
fairly stationary through the week this week. North-northwesterly
onshore flow due to the surface ridge axis being positioned to our
south will allow low-level stratus develop overnight along the coast
and the lower Columbia River. Decreased cloud cover south of this
axis later this week...but only a little due to model uncertainty on
the location of this axis. Chance of thunderstorms along the Cascade
crest due to shortwave impulses riding up along the western edge of
the upper-level ridge. These storms should mainly occur during
afternoon-evening hours...but some may linger overnight depending on
Aviation...high pressure over region...with dry southwesterly flow aloft. Like
past mornings...will see patchy fog in and around coastal bays
until 16z. In addition...coastal stratus now forming just off the
beaches. Suspect this IFR stratus will push onshore for awhile
this am...but should break up and push offshore between 16z and
18z. Otherwise...VFR with late afternoon/evening cirrus.
Kpdx and approaches...no adverse weather impacts...with VFR. Rockey.
Marine...not much change in overall weather pattern this week.
High pressure remains over the NE Pacific...with thermal low pressure over
northwest calif and far SW Oregon. Pressure gradients will flex from time to
time...but tightest gradient remains over S Oregon coastal waters
today and tonight. This will maintain gusts 20 to 25 knots through
this evening...but winds ease a tad on Tuesday and Wednesday.
Seas running 4 to 7 feet...with highest seas S of Tillamook where
duration of northwest winds continue to build up the seas. Rockey.
Pz...Small Craft Advisory for winds until midnight PDT tonight for
coastal waters from Cape Shoalwater Washington to Florence or out 60 nm.
More weather information online at...http://weather.Gov/Portland
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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.