Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 222210
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
304 PM PDT Sat Jul 22 2017

.SYNOPSIS...  A weak upper trough will pass over Washington on Sunday
for a slight increase in onshore flow bringing a bit of cooling to
to the coast and Willamette Valley. An upper ridge will build over
our area on monday and tuesday for a warning trend. An upper level
low to our southwest may produce some thunderstorms in the
Lane County Cascades Sunday through Tuesday afternoon and evening.
Increased onshore flow and cooler conditions are expected for the
second half of next week bringing temperatures back to near normal.

&&

.SHORT TERM...Saturday Night through Tuesday...Upper trough passing
by to the north on Sunday will result in some cooling of the air mass
over the region. Onshore flow will likely push marine stratus into
the Willamette Valley and southwest Washington Interior during the
early morning hours on Sunday. This afternoon temperatures should
reach the lower 90s in most valley locations but the upper trough
will result in temperatures around 5 degrees cooler Sunday.

There is a developing upper low off the coast of California which
will move to the N California coast and linger through Tuesday.
Southerly flow develops aloft ahead of the low and will likely result
in increasing moisture at mid and high levels over the southern
portion of our forecast area. Chance of thunderstorms in the Lane
County Cascades Sunday through Tuesday during heating in the
afternoon and evening hours. This appears to be the most significant
chance of lightning with the potential for fire starts in the
Cascades so far this summer.  Models show that any moisture that does
form will be high level and not likely to see any significant
percipitation from this system.  The southerly flow combines with the
upper ridge to the north of the low for warming on Tuesday...likely
shooting back in the the lower 90s in the valleys.


.LONG TERM...Tuesday night through Saturday...Models are in good
agreement kicking out the upper low over northern California t moving
it northwest during the day on Wednesday. Weak westerly flow develops
at 700mb as the low moves out it looks like the threat of
thunderstorms will be greatly reduced. However, this could change if
the upper low lingers...which they are notorious for doing this time
of year. That could prolong convection for another afternoon and
evening heating cycle.

Models show a upper trough approaching from the northwest by Thursday
which puts us back in WSW flow aloft and drys out the Cascades ending
any thunderstorm threat. Night and morning low clouds may become more
extensive Thursday through Saturday with temperatures returning to
near normal.
Schneider

&&

.AVIATION...Expect predominately VFR conditions under mostly
clear skies through tonight. Winds will continue to increase
along the coast this afternoon with gusts to 25 kt possible at
KONP and gusts to 20 kt at KAST. Gusty winds in the interior,
with gusts 15-20 kt, will continue through this evening before
subsiding by 06Z tonight. MVFR conditions look to redevelop along
the coast after 06Z tonight. Brief periods of localized IFR fog
is possible early Sunday morning in some of the more sheltered
valleys along the coast. Conditions in the interior will likely
remain VFR the next 24 hours. However, guidance continues to show
some MVFR cigs developing along the Columbia River early Sunday
morning which could bring a brief period of reduced cigs to the
metro terminals between 12-18Z, but confidence is low on whether
these cigs will impact the terminal. KTTD has the best chance of
MVFR cigs as low stratus develops along the Cascade foothills
overnight. Expect any low cigs that do develop to be brief and
lift by late Sunday morning.

KPDX AND APPROACHES...Predominately VFR the next 24 hours. Gusty
winds to 15 kt possible through around midnight tonight. There
is a chance that MVFR cigs around 2000 ft will briefly impact the
terminal between 13-17Z Sunday, but confidence is low. /64

&&

.MARINE...High pressure will continue to strengthen over the NE
Pacific this afternoon, while hot weather over SW Oregon and NW
California will help to strengthen a thermal trough over those
areas. This will bring an increase in northerly winds, with gusts
25-30 kt expected across our southern waters by sunset and
spreading north into our northern waters later tonight. The
increasing winds will result in steep wind-driven seas. Winds
will continue to increase on Sunday. Models continue to suggest
that gale force winds are possible over our southern waters.
However, northerly gales over our waters are relatively rare, so
given that the stronger models continue to only show marginal
gales will stick with our current Small Craft Advisories for
winds and hazardous seas, but would not be surprised local gusts
to 35 kt. SCA conditions look to persist into Tuesday so the
current advisories will likely need to be extended. Models then
show an upper trough from the Gulf of Alaska moving closer to our
waters which will likely bring a decrease in winds/seas towards
the middle of next week. /64

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds and hazardous seas from 8 PM
     this evening to 6 AM PDT Monday for Coastal Waters from
     Cape Shoalwater WA to Cascade Head OR out 60 nm.

     Small Craft Advisory for winds and hazardous seas until
     6 AM PDT Monday for Coastal Waters from Cascade Head OR
     to Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar from 3 AM
     to 7 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. This area is
commonly referred to as the forecast area.


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