Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 302105
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
203 PM PDT Sat Jul 30 2016

.SYNOPSIS...An upper level trough will move across the area through
the weekend, which will result in near normal daytime temperatures.
The marine layer will deepen tonight and Sunday as a weak disturbance
associated with the upper trough slides across the region. Weak high
pressure returns Monday, but a deeper upper trough is expected to
track across the Pacific Northwest Monday night through Tuesday
night. Seasonal conditions return for the middle part of next week,
followed by another upper trough late in the week.

&&

.SHORT TERM...(Tonight through Tuesday)...Nature`s air conditioner
has kicked in quite nicely, with early afternoon inland temperatures
running about 10 to 15 degrees cooler than yesterday at this time.
The KTTD-KDLS gradient has been holding steady, generally around 6 to
6.5 mb. This has produced wind gusts up to 40 mph in some of the more
exposed areas around Hood River. Water vapor imagery shows one upper
trough over Southern British Columbia, with an attendant short-wave
near the trough base. This is the feature the NAM and GFS show
sliding across Washington and Northern Oregon tonight. Another upper
low was located near 53N 153W early this afternoon.

A few areas of marine stratus persist along the South Washington and
North Oregon coast early this afternoon. The short-wave forecast to
move through tonight will deepen the marine layer. NAM soundings for
KPDX and KSLE valid 14Z Sunday nearly double the marine layer depth
compared to this morning. Soundings imply tops to near 4000 ft MSL,
but only 2500 ft MSL over KEUG. The higher resolution models, such as
the HI-RES ARW, project the marine layer to reach the North Oregon
Cascade crest and possibly make it into the Mt. Adams area valleys.
Models suggest later clearing inland, likely not until early
afternoon for valley areas north of KSLE. This also means slightly
cooler daytime temperatures compared to today.

A weak transitory 500 mb ridge moves over the forecast area late
Sunday night and Monday morning. This feature gets kicked east Monday
afternoon ahead of the next upper low. The GFS continues to be
slightly more south with the low center versus the GFS, with the NAM
closer to the ECMWF solution. Models show a fairly strong 300 mb jet
associated with this low, on the order of 100 kt. The marine layer
Monday morning will likely end up a little less extensive than Sunday
morning and have warmed Monday max temperatures slightly to account
for this trend. The upper low center moves to near Vancouver Island
06Z Tue, with the GFS maintaining a slightly more south track. The
best dynamics with this trough will be north of the Portland forecast
area. However, 12Z model runs indicate some spotty light QPF over the
far north zones Monday night and have increased POPS into the chance
category for The South Washington Coast and Willapa Hills. The bulk
of the energy moves across Washington and extreme Northern Oregon
late Monday night and Tuesday morning. The 12Z GFS hints at a little
surface-based CAPE skirting the South Washington Cascades and
foothills in northern Cowlitz and Skamania counties late Tuesday
morning into the early afternoon. Have not included any thunder
mention, but is something future shifts will need to consider.
Weishaar

.LONG TERM...(Tuesday night through Saturday)...Upper level ridging
will start to build into the Pac NW late Tuesday. Low level onshore
flow will bring the typical pattern of morning clouds and afternoon
sun. Expect a slight warming trend through Thursday, with temps near
seasonal normals.

Models continue to hint at the potential for an upper level trough
to impact the region late next week. However, the general trend has
been to keep these systems well to our north, so sensible weather
impacts to our forecast area looks to remain minimal. The good news
is that temps will cool slightly late next week, but generally
remain near seasonal normals. /64
&&

.AVIATION...VFR prevailing across the area with slowly decreasing
area of MVFR cigs on the coast north of KTMK. Onshore feed of
marine moisture kept KAST under BKN-OVC CIGS at 2500 ft, but there
is still a good chance for several hours of a SCT layer at KAST
through early evening. MVFR cigs redevelop along the coast this
evening and push inland overnight. Models indicate a stronger push
of marine air inland so expect MVFR cigs cover more of the
interior Sunday morning compared to today. Still expect interior
clouds to become scattered 18-20Z timeframe. Coastal areas may not
completely clear so expect SCT-BKN MVFR layer through Sun
afternoon.

KPDX AND APPROACHES...VFR through 08Z then increasing chances for
MVFR cigs around 2500 feet. MVFR CIGS most likely between 10Z and
20Z Sun, then VFR conditions returns. mh

&&

.MARINE...Strongest winds continue over the outer waters this
afternoon with gusts near 30 kt at buoy 46089. Winds are weaker at
buoys at 46029 and 46050. ASCAT pass from 18z confirm strongest
winds, 25 to 30 kt, over the outer waters and 15 to 20 kt near 20
nm. So far this afternoon, only a few coastal wind observations
show gusts exceeding 20 kt. Models still indicate low end small
craft advisory winds through late tonight so will keep the small
craft advisory for winds unchanged. The general trend is for the
surface high over the NE Pacific to weaken somewhat, but remain in
place through the weekend. Advisory strength winds may continue
over the central Oregon waters on Sunday, but should ease below
criteria in the north. Then expect weaker northerly winds over all
waters through around midweek, when strengthening high pressure
may bring a return to gustier northerly winds.

Seas remain quite steep over the waters due to a combination of
locally generated wind wave and a fresh swell. Models are about 2
to 3 ft too low with seas today. This is likely due to the near
gale force winds off Vancouver Island and northern WA coast
generating the fresh swell. Buoy 46089 peaked at 14 ft this
morning while buoys 46029 and 46050 peaked at 11 ft and 10 ft
respectively. Seas are peaking now and will gradually subside
tonight and should be around 7 to 9 ft on Sunday.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 2 AM PDT Sunday for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     60 nm.

     Small Craft Advisory for hazardous seas until 5 AM PDT Sunday
     for Coastal Waters from Cape Shoalwater WA to Florence OR
     out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar from 1 AM to
     4 AM PDT Sunday.

&&

$$

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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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