Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 311601
Area Forecast Discussion
National Weather Service Portland OR
901 AM PDT Wed Aug 31 2016
.SYNOPSIS...A modest cold front will move through southwest
Washington and northwest Oregon today, bringing cool temperatures and
some light rain or showers to much of the forecast area. Another
stronger disturbance or front is expected to bring more rain to the
area later Thursday and Thursday evening, followed by more showers
the remainder of Thursday night and Friday, with possibly even a few
thunderstorms Friday. A few isolated showers may linger into the
weekend otherwise expect drying into early next week. Temps will be
below normal most of the period though they may warm a little by
early next week.
.SHORT TERM...(Today through Friday)...The modest front that had been
advertised for the last several day was moving into southwest
Washington and northwest Oregon this morning. The initial rain band
on radar that was moving into the western valleys appeared associated
with the shearing upper front. The remaining bands to the west in the
coast range and along the coast appear associated with the lower
level front. This lower level front will move through the forecast
area this afternoon with some light rain. Amounts appear that they
will be modest, probably below a tenth of an inch in the valleys and
perhaps a bit more at higher elevations. Amounts in the south toward
Eugene will be less.
The front moves east of the Cascades this evening with some trailing
residual showers tonight and early Thursday, especially around the
higher terrain in the north part of the forecast area. The models all
focus in on a stronger disturbance rotating around the low off the
B.C. coast which breaks off the system out near 150w and develops
into another front that moves in later Thursday and Thursday evening.
The models suggest QPFs from this feature could reach a quarter to a
half inch or better along the coast and in the mountains,highest
north, with a tenth to a quarter or possibly even a third of and inch
in the valleys. After this front moves through Thursday evening, the
trailing showers continue through Friday in westerly flow behind the
front. The models show enough cooler air aloft sagging south to
introduce a few thunderstorms along the coast Thursday night
spreading inland Friday. May start to see a little snow in the higher
elevations of the Cascades by Friday.
Look for temps inland to be 5 to 10 degrees below normal through
Friday, with Thursday the coolest day. Tolleson
.LONG TERM...No Changes. Previous discussion follows...
(Friday Night through Tuesday)...Once the longwave trough axis shifts
east of the area on Friday, the upper NW flow pattern will become
more progressive with several weak waves moving through the area.
None of these waves appear especially strong at this time and
therefore have kept any PoP mentions in the slight chance range
through the long term period. Temperatures will moderate back to near
normal by the middle of the week, but will struggle to get much above
normal due to persistent onshore flow. /Bentley
.AVIATION...A slow moving cold front will move west to east across
the area today. MVFR to IFR cigs and occasional reductions in
visibility will continue along the coast. Inland, widespread VFR cigs
with occasional lowering to MVFR cigs and/or vsby in precipitation.
First line of more organized rain - with localized IFR conditions -
moving through I-5 corridor through 17z. Additional rounds of light
precipitation are possible through the day. Mountains will be
obscured in clouds through most of the day, with some improvement
after 08z Thu.
KPDX AND APPROACHES...VFR cigs this morning, though a line of steady
rain is approaching the terminal from the west, likely to arrive
between 16 and 18z and possibly reducing cigs/vsbys to mvfr or even
ifr at times. Showers continue through rest of today with lower VFR
to MVFR cigs likely persisting. Cullen
.MARINE...Cold front near the coast will continue onshore this
morning. Southerly winds are generally in the 10 to 15 kt today, with
seas remaining choppy and dominated by short period waves.
Winds will vary between south and southwest for the remainder of the
week. The next front nears the waters late Thursday, bringing
increasing gusts to near advisory strength. Then, stronger north
winds return late in the weekend as high pressure rebuilds over the
northeastern Pacific. Seas will remain 4 to 6 feet through much of
the week but conditions remain confused with a mix of a short period
west-northwest swell, choppy south wind wave/fresh swell, and a small
but longer period south swell also occasionally appearing in spectral
observations at times. Cullen
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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.