Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 260350
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
848 PM PDT Mon Jul 25 2016

.SYNOPSIS...A weak upper trough near the coast with a weak westerly
flow aloft over the Pacific Northwest will continue through Tuesday.
Expect morning low clouds giving way to afternoon sunshine and
seasonable afternoon temperatures. An upper level ridge will build
for the second half of the week and bring inland highs well into the
90s Thursday and Friday, before the next trough arrives to moderate
temperatures and increase clouds over the weekend.

&&

.SHORT TERM...(Today through Thursday)...Last of today`s visible
satellite loop showing solid overcast over the coastal waters and
along the coastal lowlands with clear skies inland. Stronger onshore
flow compared to Sunday is expected to bring more cloud cover inland
overnight and Tuesday.The surface pattern appears less favorable
for a push through the central Coast Range gaps, but still may see
some stratus develop in the south Willamette valley Tuesday morning.
A weak shortwave passing across northwestern Washington should bring
heights a little lower and some clouds will likely enter the northern
valley along the Columbia River and south to parts for the central
Willamette Valley, but less likely. For the northern locations, a
slightly stronger surface gradient may keep clouds in place a bit
longer, but the central coast will lie south of the surface ridge
axis and thus may be clear relatively early in the morning.

Temperatures may be somewhat cooler Tuesday from Portland to Kelso
and Cathlamet (only in the lower 80s) as a result of these clouds,
but persistence (mid 80s) looks like a good forecast for the Salem to
Eugene stretch of the valley.

For Wednesday, clouds will again be favored in the northern area, but
likely again will be rather shallow again and relatively quick to
dissipate. Flow turning more northerly may keep the central Oregon
coast largely clear or only briefly cloudy. Heights will rise again,
with 500 mb heights rising to around 588 dam and 850 mb temperatures
climbing to around 16C as a strong high over the southern Great Basin
and Desert Southwest builds north and west into the Pacific
Northwest. Onshore flow will wane as the surface ridge axis shifts
north and temperatures should again warm into the upper 80s across
the interior. The ridge begins to flatten out with heights steady
over the region by Thursday, but the air mass continues to warm, so
expect temperatures around 90 for the inland locations. Some morning
clouds possible for the northern coastal areas and along the Columbia
River, but these should be rather minimal so very warm and abundant
sunshine will be the rule for Thursday.   mh Cullen

.LONG TERM...(Thursday night through Monday)...By Thursday night and
Friday, the 850 mb temperatures will continue to nudge a bit warmer
with 588-590 dam 500 mb heights remaining over the region. With
little in the way of significant early clouds and a very warm air
mass, coupled with a relatively warm start (overnight lows 60-65 F
for the interior), Friday remains on track for the warmest day of the
week as temperatures rise into the mid 90s. Of note, while the 12z
deterministic GFS suggests cooler temperatures than some of the other
model guidance, it does lie on the extreme cool side of the GEFS
envelope. However, there does remain some uncertainty in just how
warm temperatures will be on Friday. By Saturday, the next upper
trough drops from the Gulf of Alaska into northwestern Washington or
southern B.C., with the associated surface front sweeping across the
region by Saturday night or earlier Sunday. As a result, the
temperature forecast for the transition days - particularly, Saturday
- remains rather tricky. For now, will maintain Saturday in the upper
80s ahead of the front and Sunday in the upper 70s to around 80s with
additional clouds moving into the area. The deterministic GFS is
again the quickest to cool things off, but with the GEFS ensemble
mean and particularly the ECMWF transitioning the pattern at a more
moderate pace, will continue to keep the forecast in this direction
for now. Regardless, very limited deep moisture with this system
means that PoPs were maintained generally 10 percent or less through
the weekend period.   Cullen

&&

.AVIATION...IFR to low end MVFR clouds have remained packed
onto most of the coastal areas this evening. With onshore pres
gradients generally stronger than the same time last night and
another short wave expected to reach the coast late tonight, expect
marine clouds to spread into the Willamette Valley late tonight and
tue morning. With the surface ridge extending into nw OR this
evening, the most favorable locations to see development of probably
MVFR cigs will ne in the north Valley, specifically KPDX and KTTD
between 10Z and 14Z. Other locations are more likely to remain VFR
with just a chance of MVFR cigs after 13Z. Expect whatever develops
inland to break up and return to VFR conditions between 18Z and 21Z
Tue. Along the coast MVFR and pockets of IFR cigs are likely to
continue through tonight and Tue.

KPDX AND APPROACHES...VFR conditions expected through late tonight.
Marine clouds with MVFR cigs expected to develop late tonight and
Tue morning between 10Z and 14Z...then eventually break up
again between 19Z and 21Z.

&&

.MARINE...Winds over the waters have picked up this evening
across the coastal waters, but at this point have come up a little
short of small craft conditions. While pres gradients through the
night are expected to allow winds to continue, climatology tells us
it is unlikely to increase much more. While it looks close, at this
point prefer to drop the Small Craft Advisory for winds for tonight,
and limit peak winds to around 20 kt.

There will be little change the next several days as north winds
persist over the waters and wind waves remaining the primary sea
influence. The thermal induced trough of low pres will continue to
expand slightly north in the afternoons and evenings for an increase
in gusty winds, with the strongest pres gradients south of Cascade
head. The trough will expand further north Wed through Fri for a
better chance of small craft winds for the N OR/S WA waters in the
afternoons and evenings.

Seas remain choppy under the influence of short-period (4 to 5
second) wind waves. A developing fresh swell due to the locally
generated fetch from the persistent north winds, increase steep
waves around 10 seconds. There is also a very small (1 ft or less)
long-period south swell that the buoys will occasionally detect.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.

&&

$$

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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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