Area Forecast Discussion
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FXUS66 KPQR 221647

Area Forecast Discussion
National Weather Service Portland Oregon
947 AM PDT Sat Oct 22 2016

.SYNOPSIS...Low clouds and fog in the interior valleys should clear
this morning, but may persist into the early afternoon for areas
south of Salem. A developing low pressure off of the Oregon coast
will bring a cold front onshore tonight. Another surface low over the
Gulf of Alaska will move south and develop into a stronger low
offshore of Oregon Sunday for another front across the region Monday.
The low will remain offshore through at least Tuesday and maintain
unsettled weather for the region.


.UPDATE...Showers have ended over the area early this morning and fog
filled in the interior valleys. The fog is now lifting in most areas
to a thin cloud deck, and clouds have cleared all together in some
spots. The central and south Willamette Valley are hanging on to the
fog the longest with patches of dense fog remaining between Salem and
Eugene as of 840 AM. The fog will gradually improve in these places
as well and expect brief clearing of the skies late this morning and
early this afternoon before the next system arrives.

A surface low is deepening around around 300 miles off of the Oregon
coast this morning. The low center moved over the offshore buoy
#46005 around 8 am this morning and measured a mean sea level
pressure of 1003 mb. Satellite imagery shows that the low is still
deepening and MSAS 3-hour pressure change suggests that the low is
tracking NNE towards the BC Coast.  The 12z model data is starting
to come in and is initializing well with the buoy and satellite
readings. The NAM is initializing slightly better than the 12z GFS
and forecasts the low to deepen to a 990mb low off of the BC coast
late tonight.

The strongest winds with this low will remain well offshore and north
of the Portland forecast area. The south Washington and north Oregon
coasts could see gusts up to 25 to 30 mph when the associated surface
front nears and passes through tonight. The front will bring light
rain to the coast this evening with showers inland late tonight into
early Sunday morning. THe rain will be most organized over the coast
and coast range tonight, but the totals should be less than 0.25
inch. Inland, the rain will be more spotty with totals less than 0.15
inch. TJ

Previous SHORT TERM from 313 AM Saturday...Today through Monday...NWS
Doppler Radar continues to show a few stubborn showers north of a
Tillamook to Mt Hood line this morning, though they do seem to be
finally dissipating as shortwave ridging moves into the region. Weak
high pressure is allowing for some clearing, but with the ground so
moist it is not taking long for fog to form in valleys where skies
are clearing. With the sun angle getting lower this time of year,
light winds, and high clouds expected to be on the increase
throughout the day, it may take some time for the fog and low clouds
to completely burn off...perhaps midday or early afternoon. Decided
to keep temps a couple degrees below most guidance in the valleys
today to account for potentially more persistent cloudiness. Most
lowlands should see highs near 60 degrees today.

Satellite water vapor imagery is showing a compact, rapidly
developing low near 44N/134W as of 09z this morning. This system is
producing a number of lightning strikes, indicating the rapid
intensification. Models seem to be struggling to keep up with the
strength of this system, but given the sharp left turn this system is
expected to take, the impacts on the forecast may be minimal - at
least for our land zones. Collaboration with WPC/OPC helped determine
that the ECMWF was the better of the 00z runs in initializing this
system, showing 1006 mb by 06z while others were shallower. The bulk
of the energy with this system will shift north toward the BC coast
this afternoon and evening, but it will push a weakening frontal
system into western WA/OR tonight into Sunday. The 00z EC does show a
little coastal wind tonight...probably gusts 30-40 mph beaches and
headlands. Otherwise the main impact will be some areas of light to
moderate rain spreading inland overnight into Sunday morning, then
dissipating as the front loses its upper level support later Sunday.

Another upper low is presently digging south across the Gulf of
Alaska. This system is also expected to rapidly intensify in the
general vicinity of 45N/135W Sun/Sun night. Models are very bullish
in the depth of this low, with many showing central pressure around
965-970 mb by Monday morning. However, the system is expected to
remain far enough offshore to mitigate wind potential for most of the
forecast area. The low will push an occluding frontal system across
the Oregon coast Monday morning. While the deepest moisture is
expected to be aimed toward the OR/CA border, occasional rain is
still expected across much of our CWA Monday. The cloud cover and
rain should keep temps in the 50s for the lower elevations Monday.
However snow levels should generally remain above pass level through
Monday.  Weagle

.LONG TERM...No Changes. Previous discussion follows...(Monday night
through Friday)...Much uncertainty in the extended, as the models
diverge significantly later next week. A broad low pressure system
remains off the Coast of Washington and Oregon through the first half
of next week.  The front associated with the occlusion of the Low
moves through on Monday bringing rain across the area. Tuesday is
when the models start to diverge significantly. The GFS brings a
shortwave up the Coast bringing another round of moderate to heavier
rainfall on Tuesday night into early Wednesday. The ECMWF is slower
bringing this system up the Coast, keeping us mostly dry on Tuesday,
except some light rain along the Coast. This model brings the midweek
system through on Wednesday into Thursday. Beyond midweek, there
appears to be either a cutoff system that sets up a rex-block pattern
through the end of the week, or a broad upper-level trough that keeps
us rainy into next weekend. If the rex block sets up, we could be dry
into next weekend. So essentially, flip a coin for whether it will be
wet or dry going into next weekend. Snow levels next week are
expected to stay up above 6000 feet, so snow should not be an issue
if your traveling across the passes this week. -McCoy


.AVIATION...Continues to be a mix of flight conditions across the
area, though we are seeing VFR conditions at coastal terminals.
Inland the fog and low stratus appears to be scattering out
slowly east to west, with VFR conditions already at KTTD and
mostly VFR conditions at PDX. Farther south, fog has persisted,
though appears to be starting to break up. Expecting to see mostly
VFR conditions at all sites by 19Z today, with clear skies through
midday. Will start to see increasing upper level clouds this
afternoon with the approach of a weak frontal system this evening.
Cigs with this system should only get down to around 5000 ft, so
expecting predominantly VFR conditions across the area to persist
through tonight. Can`t rule out some patchy fog impacting a few
terminals late tonight into Sunday morning, mainly after 06Z this

KPDX AND APPROACHES...600 ft stratus should be mostly gone in the
next hour for VFR clear conditions through midday today. Will see
increasing high clouds this afternoon lowering to around 5000 ft
around 07Z tonight. -McCoy


.MARINE...A longer period westerly swell pushed seas into the low
to mid teens this morning. Seas have dropped back down to 10 to 12
ft this morning and should remain around 10 to 12 ft through this
evening. A rapidly developing low pres system apparent on
satellite near 47N/130W will lift north toward Vancouver Island
tonight. Although our coastal waters looks to be spared from the
strongest winds, S to SE winds will pick up quickly later this
afternoon and evening. Expect 20 to 25 kt winds with gusts to 30
kt into early Sun AM. There is potential for a few low-end gale
force gusts over the northern waters, but looking less likely so
will stay with a Small Craft Advisory for today unless a
significant shift occurs. The winds will bring increasing
southerly wind waves, which will keep seas above 10 ft through
early Sun.

After a lull for much of Sun, another potentially much stronger
system is on tap for Sun night into Mon. There are significant
differences in model strength and track at this time. But felt
confident enough in the overall pattern to issue a Gale Watch
from Sun evening through Mon morning. The current fcst contains
S-SE winds 30 to 35 kt with gusts to 40 kt. It appears that there
is potential for winds to be even higher. This system will likely
push seas at least into the mid teens, possibly pushing 20 ft.

Low pres remains over the NE Pac through at least the first half
of next week. Additional strong frontal systems look likely every
24 hrs or so through Wed. There are signs that the weather could
quiet down somewhat for the second half of the week. McCoy/Pyle


PZ...Gale Watch from Sunday evening through Monday morning for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     60 nm.

     Small Craft Advisory for winds from 3 PM this afternoon to 5 AM
     PDT Sunday for Waters from Cape Shoalwater WA to Florence
     OR from 10 to 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 winds from 8 PM this evening to 5 AM
     PDT Sunday for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 10 nm.

     Small Craft Advisory for Rough Columbia River Bar until 2 PM
     PDT this afternoon.

     Small Craft Advisory for Rough Columbia River Bar from 8 PM
     this evening to 5 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. is the U.S. government's official web portal to all federal, state and local government web resources and services.