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Area forecast discussion 
National Weather Service Portland or
307 am PDT Tuesday Jul 29 2014

Synopsis...an upper level ridge will be centered inland over the
Pacific northwest through this week with an upper low centered off
the b.C. Coast. The resulting light southwest flow aloft will produce
very warm and dry weather to southwest Washington and northwest
Oregon. There is a chance for thunderstorms in the Oregon Cascades
in the afternoons and evenings. The marine layer will be shallow but
is more solid...with a little seepage through the coastal gaps
expected as the week progresses.
&&

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 features
affecting the weather for the Pacific northwest this week. Light
mostly southwest flow aloft with high 500 mb heights. The marine
layer remains shallow under the subsidence aloft and is limited to
the coastal zones with a little seepage up the lower Columbia River.

Very similar conditions today. The main differences are lower 500mb
heights for a slightly cooler air mass along with an increase in the
low level onshore flow. This will keep the marine stratus along the
coast today. Later tonight into Wednesday morning an old frontal boundary
slides into the coastal waters and may bring some drizzle to the
coast.Marine stratus should seep further inland and try to extend
inland to near Portland but anything will be very brief and not have
much impact. Temperatures inland will continue to be very warm with little
change through Thursday.

As for thunderstorm activity...another batch of moisture arrives into
the southern zones this afternoon. Instability is limited for cloud
growth up to the -30c level and will likely need the higher terrain
of the Cascades to initiate convection. So expect any convection to
be isolated at best. However with the increased moisture a strong
cell could dump a fair amount of precipitation in a short time. The pattern
Wednesday and Thursday looks very similar to Tuesday...with a chance
of thunderstorms again over the Cascades in the afternoon and
evening. One change in the models...precipitable water values are
down to 0.6 inch from 1 inch over yesterdays run.



Long term...Thursday night through Monday. The ridge in place over
the western U.S. Will remain in place through the end of the week. A
series of shortwaves are forecast to travel up the west side of the
ridge...possibly impacting our area. These impulses bring chances
for thunderstorms...mainly in the Cascades...through the weekend.
Model uncertainty exists on the timing and strength of these
shortwaves as model resolution accuracy declines rapidly further in
the forecast period...especially for these smaller features. Have
decreased probability of precipitation further north on Friday as the models have converged
on a more southerly track for storm chances...and decreased
confidence of thunder chance over the weekend due to great model
uncertainty on timing and location. -McCoy

&&

Aviation...LIFR/IFR stratus and fog remain in place early this
morning along the S Washington and north and central Oregon coast. This
coastal stratus should burn back offshore by early this
afternoon...around 19-20z. May linger a bit longer along the
central coast along konp...but do expect some clearing to occur at
least briefly. Coastal stratus returns again by late tonight. Gusty
north winds along the coast 19z-03z. Dry SW flow aloft and high pressure
should maintain VFR conditions across the interior taf sites next
24 hours.

Kpdx and approaches...VFR prevailing next 24 hours with generally
light north-northwest surface winds. Cullen

&&

Marine...few changes in the weather pattern over the waters this
week as north to northwest flow remains in control given high pressure over the
NE Pacific and a thermally induced surface trough over northwest California and
extreme SW Oregon. A few subtle changes in surface pressure
gradient...but looks like gradient remains strongest over the
inner waters. With only slight variations in surface pattern for
today...maintained a largely persistence based forecast for winds.
Small Craft Advisory for the inner waters this afternoon and
evening...and expect wind gusts over the outer waters to top out
around 20 knots though cannot rule out a few occasional small craft
gusts over the outer waters.

Seas generally running 4 to 6 feet over the next several days with
only small background swell. Thus seas will be primarily wind
dominated through the week and conditions may be choppy at
times...particularly in the afternoon and evening hours...in
response to the strongest winds. Cullen

&&

Pqr watches/warnings/advisories...
or...WA...none.
Pz...Small Craft Advisory for winds from 2 PM this afternoon to 11
PM PDT this evening for coastal waters from Cape Shoalwater Washington
to Florence or out 10 nm.

&&

$$

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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.

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