Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 241045
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
344 AM PDT Wed May 24 2017

.SYNOPSIS...An upper level trough will continue to carve out over
Washington and Oregon today, with a disturbance moving through that
will maintain the onshore flow and clouds and produce some drizzle or
light showers especially north. The upper trough will linger through
Thursday with some late day thunderstorms possible over the Cascades
but some afternoon sunshine west of the Cascades. High pressure will
return Friday for drier, sunnier, and warmer weather. Warm and dry
conditions continue through the holiday weekend though a few late day
thunderstorms may be possible again over the Cascades early next
week.
&&

.SHORT TERM...Today through Friday...An upper trough will continue to
carve out over Washington and Oregon today in the wake of the rather
brisk system that brought a strong marine push to the forecast area
with breezy to windy conditions late Tuesday and Tuesday night. Temps
in the valleys today will be around 20 degrees cooler than on Tuesday
as onshore flow continues. While cloud cover has been somewhat broken
up overnight in the wake of the weak frontal boundary from Tuesday, a
disturbance dropping down into the upper trough over the area will
reinforce the clouds through the day today, possibly producing a bit
of drizzle or a few light showers especially north of about Salem.

The main upper trough will linger Thursday, with the models continue
to indicate that some backdoor convection over the Cascades is likely
Thursday afternoon and evening as moisture and instability on the
back side of the upper trough moves through. West of the Cascades
should see a fair amount of morning clouds before breaking up some in
the afternoon and letting some sunshine through. Guidance suggests
that valley temps will rise onto the lower to mid 70s on Thursday.

Clouds will continue to decrease Thursday night and Friday as the
upper trough moves east and an upper ridge moves in. Friday looks
pretty warm as 850 temps suggest valley temps will reach the lower to
mid 80s under plenty of sunshine after local morning clouds as a
touch of summer returns. Tolleson

.LONG TERM...Friday night through Tuesday. The models continue a
decent amount of agreement with a fairly strong upper ridge over the
Pacific Northwest this weekend that begins to edge slowly eastward
early next week. The models show some indications of convection over
the higher Cascades in the late afternoon and evenings beginning late
Sunday. The threat of late day convection continues through early
next week over the Cascades. Have lowered temps some around Tuesday
and Wednesday as the models show southwest flow aloft will lead to a
developing marine layer near the coast that will begin spreading
inland. Tolleson
&&

.AVIATION...Tough aviation forecast this morning as stratus did not
come in quite as guidance suggested. Based on satellite imagery, a
more solid mass of marine stratus appears to be heading toward the
Coast and will make it to AST around 12Z. This will progress down the
Coast, making it to ONP by 13-14Z. Still think there is a decent
chance for low stratus with cigs around 2500-3000 ft to make an
appearance after sunrise this morning, with stratus currently butted
up against the foothills of the Cascades backbuilding into the
Willamette Valley, but this may be more broken meaning it may not
impact all terminals. This low stratus inland, if it develops, should
break up and lift to around 5000 ft by 16-18Z for VFR conditions
inland through tonight. The Coast, however, appears likely to hold on
to stratus with around 2500-3000 ft through tonight.

KPDX AND APPROACHES...VFR conditions this morning. 50 percent chance
of stratus impacting the terminal from 14Z-17Z. After 17Z, low
stratus breaks up and broken cigs lift to around 5000 ft and persist
through tonight. -McCoy
&&

.MARINE...Pattern continues with high pressure over the NE Pacific
and a thermal low inland combining to continue SCA wind gusts through
at least tonight. Will see decreasing winds overnight tonight as the
thermal low moves off to the east and the pressure gradient decreases
across the waters. Will first see winds within 10 nm of the Coast
drop below SCA criteria later tonight, and then across the entire
waters Thursday morning. Benign conditions look to reign Thursday
afternoon through this weekend as the pressure gradient remains
relatively week across the waters.

Seas have come up a bit higher than forecast, particularly in the
northern waters where we have been seeing seas up around 9 to 11 ft.
Seas are very steep across all our waters with dominant wave periods
around 6 to 8 seconds. Expect seas to back down a bit this morning
before building back up near 10 ft this evening. Expect short wave
periods to continue through at least this morning. May need to extend
it through this evening if the background fresh swell never overtakes
the wind-wave component and dominant wave periods don`t increase to
10 to 12 seconds. Low confidence in when this may happen. Seas will
start to ease Thursday and little threat of notable seas affecting
the waters through the weekend. -McCoy

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 8 AM PDT Thursday for
     Waters from Cape Shoalwater WA to Florence OR from 10 to
     60 nm.

     Small Craft Advisory for hazardous seas until 11 AM PDT this
     morning for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 nm.

     Small Craft Advisory for winds until 11 PM PDT this evening for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     10 nm.

     Small Craft Advisory for Rough Columbia River Bar until 7 AM
     PDT this morning.

&&

$$

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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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