Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Portland or
242 am PST Sat Feb 6 2016
Synopsis...lingering showers ending today. Then dry for next 3 to 4
days as high pressure builds over the region. Will have increasing
offshore flow later sun and Monday...which will warm the air mass for
Short term...today through Tuesday...
upper trough pushing over the region this am... with isolated
showers. These showers will end later today as the upper trough moves
farther east into the northern rockies. The best threat of showers will be
over the mountains north of a Tillamook to Montana Hood line.
Otherwise...variable cloudiness over the region...with some large
areas of open skies. In these open sky areas...will see areas of fog
and low clouds form...mainly from Salem southward. Most areas will
see partly cloudy skies today.
As high pressure builds into the region tonight...skies will clear.
However...with light winds and still damp ground...should see
widespread fog/low clouds later this evening and persist well into
sun am. Offshore flow not all that strong until later Sun afternoon.
So...low clouds will clear off quickly along the coast and near
Columbia River...but elsewhere stratus will be much more stubborn in
clearing. As result...have lowered temperatures to the upper 40s/low 50s in
those areas such as to south of Salem and Cowlitz valley where clouds
will persist longer on sun.
East winds through The Gorge to increase Sun night as the gradient
through The Gorge gets up to at least 7 mb...however this still looks
like a gap flow event. This gradient supports gusts to around 50 miles per hour
at Corbett and Rooster Rock...and much higher at Crown
Point...perhaps 60 to 70 miles per hour. Look for low stratus and fog to bank up
against Parkdale/Hood River Valley starting later Sun night. Expect
fog/low clouds to redevelop in valleys away from gorge.
The warming that begins in the Coast Range and foothills on Sunday
due to the building upper ridge will increase Monday...and the peak
of the inversion on model soundings indicate that lower to middle 60s
are possible in the middle level slopes of the Cascades and in the Coast
Mountains the low sun angle for early February and the east winds through
The Gorge will work to maintain the valley inversions and cooler
temperatures in the lower valleys.
Long term...Tuesday night through Friday...little change in the
forecast through Wednesday as a strong upper level ridge persists
over the Pacific northwest. Expect warm and dry conditions under weak offshore
flow. Light winds will also allow patchy fog to develop overnight
through early Wednesday over much of the interior. The fog will
likely burn off late in the morning...but would not be surprised if
it persists into the afternoon. Moderate east winds near the Columbia
River gorge will help limit fog development in the North Valley.
Temperatures are expected to climb near 60 early next week...but if the fog
lingers we could see slightly cooler temperatures. Our next shot at rain
arrives late Wednesday as a weak shortwave brings a stretching front
across the Pacific northwest. This will help open the door for an active weather
pattern...with wet weather likely continuing late next week. /64
Aviation...a few showers lingering this morning behind last
nights cold frontal passage. Showers to taper off later this
morning...with clouds scattering this afternoon. Expect mainly
VFR conditions through this evening. However...there is chance for
some patchy fog or low stratus over the central and southern
Willamette Valley between 12z and 18z. Westerly 850 mb flow of 20-30
knots will result in MVFR or worse conditions over the higher
terrain with frequent obscurement through this morning.
Kpdx and approaches...expect mainly VFR conditions through
tonight. There is a chance for a passing shower this am...
then cloud cover scatters considerably this afternoon. Pyle
Marine...westerly Post-cold frontal winds are gradually subsiding
this morning. Have dropped the Small Craft Advisory for winds for
the central Oregon waters. Will maintain the small craft for the
northern waters through 12z this morning. Then winds to remain
below 20 knots through this evening. A warm front will bring
increasing winds again late tonight into Sun morning...mainly over
the northern outer waters. Expect southerly winds of 15 to 20 knots
with gusts to 25 knots. Offshore flow pattern develops Sunday and
will last into the middle of next week. Another warm front is
modeled to bring increasing southerly winds again Tuesday night into
Seas remain above 10 feet through this evening. Latest guidance
still shows seas building just above 10 feet late Sun night or
Monday...then falling back below 10 feet Monday night. A longer period
westerly swell is modeled to arrive during the second half of next
Pz...Small Craft Advisory for winds until 4 am this am for the
northern coastal waters...or from Cape Shoalwater to
Small Craft Advisory for hazardous seas until 10 PM this
evening on all waters from Cape Shoalwater to Florence.
Small Craft Advisory for rough Columbia River conditions
until 7 PM today.
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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.