Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 280344
Area Forecast Discussion
National Weather Service Portland OR
841 PM PDT Mon Mar 27 2017
.SYNOPSIS...Showers decreasing this evening. But high clouds
associated with an approaching warm front will be increasing tonight.
Rain should hold offshore, but clip as far south as Tillamook later
tonight. Rain will gradually spread south and east across the region
later Tue into Tue evening, then transition to showers Wed afternoon
into Thu. But, trend for somewhat drier weather later Thu. In fact,
high pres still looks to be enough to keep Fri and probably Sat dry
.SHORT TERM...(Tonight through Thursday)...Showers winding down over
much of the forecast areas this evening and should be ending after
midnight. Radar signature shows light rain over the coastal waters
and even reaching the coast north of about Pacific City, OR. Models
indicate rain from a warm front offshore should be limited to west of
the coast range ridge but may spill further inland in southwest
Washington and far north zones in NW Oregon late tonight and Tuesday.
In fact, with the warm front lifting north of the region on Tue, will
see some thinner spots in the clouds to south of Salem. Generally,
will keep areas south of a Lincoln City to Portland line dry for Tue
afternoon. With mild air mass, temperatures will stay in the middle
to upper 50s. If can get some bigger breaks in the cloud cover on
Tue, would not be surprised if areas to south of Salem break into the
lower 60s. Meanwhile, freezing levels will be on the rise later Tue
and Tue night, running between 7000 and 8000 feet Tue night into Wed.
Models continue to show the cold frontal boundary approaching Tue
night, with rain spreading back to the coast in the evening, then
spreading inland overnight. The cold front will buckle inland Wed am
with rain transitioning to showers by Wed afternoon. But, will see
a 1007 mb low pres on the front develop off the south Oregon coast.
This will act to hold up the front, and slows its inland progression.
So, will likely see rain continue all day on Wed for areas south of
Newport to Salem to Mt Hood. Precipitable water values running fairly
high, as this front will have prior tapped some moist subtropical
air. Will keep mention of locally heavy rain for the coast, Coast
Range, and Willapa Hills for later Tue night into Wed am. Rather
modest rainfall expected for Tue night and Wed expected, with 0.75 to
1.50 inch on the coast, with 1 to 2 inches in the Coast Range/Willapa
Hills. Farther inland, generally 0.50 to 1.00 inch likely for the
lowlands, with 0.75 to 1.50 inches in the Cascades. Unfortunately,
this will fall as rain for the Cascades, thanks to the elevated
Once the frontal boundary shifts farther south and east, likely Wed
evening, will see showers gradually decrease. Upper trough axis will
shift over the region late Wed night into Thu am, with best threat of
showers at that time. Thu likely to be similar to today, with a
decreasing shower threat as the day progresses. Rockey.
.LONG TERM...(Thu night through Monday)... Model agreement is better
through Fri and Sat, with a more progressive pattern over the region.
Models continue to show ridging over the region by Fri, with dry and
mild temperatures. Still differences in the models, but will maintain
dry weather into Sat. But, will trend back to some chance of showers
for Sat night and Sun as will see another front shift across the
region at that time. With the progressive pattern, will see fronts
moving across the region about every 2 days. So, after Sunday, will
transition to another decreasing shower day on Monday, with
potentially another dry day or two to start next week. However, since
it is spring and Mother Nature can get feisty at times, will keep
some mention of showers to start next week./mh Rockey.
.AVIATION...Generally VFR across the area this evening, except
for isolated MVFR conditions along the S Washington and North
Oregon coast. Expect VFR conditions through about 12Z Tue. Warm-
frontal precipitation spreads across SW Washington and NW Oregon,
mainly north of a KSLE to KTMK line late tonight or around
sunrise. This should produce areas of MVFR, especially along the
coast of KTMK. Warm front lifts a little north in the afternoon.
Areas south of the KSLE to KTMK line to remain VFR through Tue
KPDX AND APPROACHES...VFR at the terminal and vicinity as of 03Z.
VFR to prevail at the terminal through Tue afternoon, but there
is a threat of -RA 12Z through 18Z. MVFR cigs possible in the
Tualatin Valley 12Z-18Z. Weishaar
.MARINE...Little change in the forecast this evening. 00Z NAM in
line with previous runs and the GFS showing small craft advisory
level wind developing over the waters overnight. Advisory start
time may be a little early, but will leave it as is. Gusts up to
30 kt likely in the north waters Tue. Gale force wind expected
Tue evening through Wed morning.
Seas will build to around 15 ft overnight and remain 13 to 15 ft
through Wed. Hanson plots and spectral guidance suggest a 11 to
12 second swell set and a longer-period 17 to 18 second swell
train tonight through Tue. Weishaar
PZ...Small Craft Advisory for winds from 11 PM this evening to 11 PM
PDT Tuesday for Coastal Waters from Cape Shoalwater WA to
Florence OR out 60 nm.
Small Craft Advisory for hazardous seas until 11 PM PDT Tuesday
for Coastal Waters from Cape Shoalwater WA to Florence OR
out 60 nm.
Small Craft Advisory for Rough Columbia River Bar until 11 PM
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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.