Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus66 kpqr 120440 aaa 
afdpqr

Area forecast discussion...update
National Weather Service Portland or
939 PM PST Mon Nov 11 2019

Updated aviation discussion

Synopsis...dry tonight, but rain and clouds return for Tuesday.
Weakening front will push inland on Tuesday. Then, we enter the
Market for rain about every other day, with the next round of rain
arriving on Thu and Fri, and then again later Sat into sun. Appears
that mother nature will decided enough was enough. Back to authentic
pac northwest November weather.

&&

Short term...tonight through Thursday...rather nice afternoon across
much of the region, with temperatures in the 60s, and even close to
70 deg along the Oregon coast. This thanks to the offshore easterly
winds. High pressure over eastern wash/ore has provided some welcomed
offshore flow, with easterly winds bringing more fresh air into our
area. Air quality has improved, enough that can not support the
continuation of air stagnation advisory. So, will end the advisory.

Offshore pressure gradient across the Columbia Gorge, from The
Dalles to Troutdale, peaked near 7.0 mb around midday, and are now
down to 5.5 to 6 mb. This will be enough to maintain breezy east
winds in the western Columbia Gorge through this evening, with gusts
30 to 40 mph but locally up to 50 mph such as at Crown Point. Closer
to the Metro, gusts generally 20 to 30 mph, with strongest at
Troutdale. Winds will gradually east tonight into Tue.

Models continue to show weak upper short wave offshore that will push
around the upper ridge and drop into the pac northwest on Tue. This will
allow a weak front to push east, coming onshore early Tue and pushing
to the Cascades by late afternoon. Not unlike the previous
front from late last week, some tropical moisture has been entrained
into this system as seen in satellite imagery, and GFS continues to
suggest precipitable water values on the order of 1.0" to 1.2" as
the front across the region. Best dynamics will be across the
north part of the forecast area, with chances for rain ranging from
categorical (80 pct or more) in the north to chance (30 to 50 pct)
across southern Lane County. Rain will quickly end Tue evening, as
the upper support and front shift east of the region.

By Wed, models are quick to restrengthen the upper ridge over
the region, allowing another round of light to moderate offshore
flow. Strong subsidence along with initially moist low levels suggest
plenty of fog or low clouds are likely to develop Tue night and
persist into Wed morning. Still, not too bad for Wed and Wed night.
Again, with area between systems, will see mostly dry weather for
variable clouds, and of course, some fog at times.

Changes arrive on Thu, as yet another front arrives. Timing is such
that will have increasing clouds. Models have been slowing the
arrival the front, with rain developing along the coast later in the
afternoon. Will keep inland areas dry during the day. /Rockey

Long term...Thursday night through Sunday...still have rather
progressive pattern returning to the region for later this week and
lasting into next week. First to deal with is the front that will be
pushing arriving late Thu and Thu night. Timing such that think will
trend towards GFS/European model (ecmwf) and slow this down a bit more. So, bulk of
rain will be Thu night into early Fri am. Generally, looks like could
get up to an inch of rain over the higher terrain, and 0.25 to 0.50
inch elsewhere. Snow levels stays elevated, above 7000 feet.

Looks like will see another brief break for Fri night into Sat, but
another frontal system will approach this weekend. At moment, warm
front will buckle north over the region later Sat and Sat night, with
rain. Following cold front will push inland on sun, with rain
transition over to showers Sun night. This system will likely have
some decent rainfall, with potential of 1 to 3 inches over the coast
mtns and into the Cascades, with 0.50 to 1.00 inch for interior
lowlands. This idea is further supported with ivt( integrated water
vapor transport) showing decent plume off the tropical pac into the
pac northwest for Sat night into sun. So, looks like a rather wet weekend
for the region, with rather high snow levels. Rockey.

&&

Aviation...high pressure is keeping conditions fairly stable and
quiet tonight. Offshore flow is creating gusty conditions through
The Gorge with a peak gust reported of 31 kt at kttd Tue night.
Easterly flow will persist through around 15z Tue as a weak warm
front moves over the area. This front will stay generally north
of keug bringing rainfall and a wind shift with it. The front is
moving fairly quickly and will pass through the area by 00z Wed.
As the front approaches the coastline around 10z Tue, there is a
chance for some fog development in the southern Willamette
Valley where conditions have remained fairly clear through the
afternoon and evening. Some fog has already formed around keug,
but at this time it is fairly localized.

The challenge will be regarding more widespread fog development
overnight. Due to the winds in the north, there should be enough
mixing to keep areas around Portland fog free. The influx of
stratus around the time of maximum cooling (around 13z wed) may
keep more widespread fog at Bay.

Kpdx and approaches...easterly flow will continue through the
period however winds are beginning to weaken tonight. VFR
ceilings will persist through around 18z Tue when the warm front
will move over the Airport dropping ceilings to MVFR around
1000-2000 ft above ground level. Rain is expected through around 00z Wed. Weak
high pressure will build in again behind the front. -Muessle

&&

Marine...previous discussion follows. Winds will continue to
relax through Tuesday as the gradient weakens thanks to the warm
front slowly approaching and lifting to the north. Southerly
winds stay in the 5 to 10 kt range, with 4 to 7 ft seas with a 10
to 13 second period through the middle of this week.

Models continue to show a front arriving Thursday, bringing
the potential for small craft gusts up to 25 kt. However, the
overall pattern with the past few systems have shown a weakening
trend with each new model run. Expect a fresh westerly swell
behind the front, with seas getting up to 10 to 13 ft. Another
front will arrive later next Sat into sun, which could also bring
Small Craft Advisory winds into our waters. -42

&&

Pqr watches/warnings/advisories...
or...none.

Washington...none.

Pz...none.

&&

$$

Interact with US via social media:
www.Facebook.Com/nwsportland
www.Twitter.Com/nwsportland

National Weather Service Glossary of Abbreviations