National Weather Service Raw Text Product

692 
FXUS66 KPQR 172312
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR 
412 PM PDT Fri Mar 17 2017

.SYNOPSIS...A warm front continues to push slowly northward across NW
Oregon this afternoon. Steady rain to the north of the front will
taper to showers with gusty south winds this evening. Low pressure
well off the Oregon and northern California coast will move northeast
and make landfall on the Olympic Peninsula later tonight or early Sat
morning. The associated cold front will reach the coast around the
same time, then push inland Saturday. Snow levels will be well above
the Cascade passes tonight, but fall below pass level by Saturday
afternoon. High pressure returns Saturday night and Sunday for a
brief drying trend. A more moist south flow aloft develops Monday and
continues through at least Tuesday night for an increasing threat of
precipitation. An unsettled pattern persists during the latter half
of next week.  

&&

.SHORT TERM...Tonight through Monday...Diffuse low pressure off the
Oregon and northern California coast will continue northeast, making
landfall on the Olympic Peninsula later tonight or early Saturday
morning. This system continues to push a warm front slowly northward
across NW Oregon, which is expected to cross the Columbia into
Washington this evening. To the north of the warm front, plenty of
isentropic lift has resulted in several hours of steady light to
moderate rain; the back edge of which is near Salem as of 345 pm this
afternoon. In the warm sector south of the front, precipitation is
more showery in nature...with temps generally in the 50s. Tonight
should be a mild night for much of the district, with increasing
south winds as the associated cold front approaches the coast. 18z
NAM/GFS did not change much from previous runs...with 850 mb winds
S-SW on the order of 55-65 kt ahead of the cold front. While it is
possible a couple of our windier coastal sites could briefly touch
55-60 mph gusts, winds are generally expected to remain below warning
criteria. Models appear a little overdone with the wind profile given
the modest pressure gradients. The secondary low/trough within the
southern part of our complex low (presently near 38N/135W) may also
rob some of the S-N gradient as the cold front pushes onshore and
across our forecast area later tonight and Sat morning.

The secondary wave of low pressure also slows down the progress of
the cold front a bit...which will probably boost rainfall totals
across the CWA as light to moderate stratiform rain continues near
the front well into Sat. Overall, expect about 0.50 inch for the
inland valleys with 1-2 inches along the coast and in the higher
terrain. A couple of the wetter spots in the Coast Range and S WA
Cascades may approach 3 inches of rain from this system. While not
likely enough to create hydrologic issues by itself, the mild rain
ahead of the cold front will likely add to snowmelt and keep rivers
fairly high for the next few days. 

Mild air advecting in with the warm front will generally
keep snow levels above the Cascade Passes for much of this event,
though snow levels will drop back to pass level or lower Saturday as
the cold front moves through. While some of the higher ski resort
elevations may eek out 6 inches of snow out of this system Saturday,
these accumulations do not appear to be widespread enough to warrant
an advisory. 

Post-frontal showers will linger into Sat night, ending by Sunday as
cool high pressure builds into the Pac NW. After a wet Saturday,
Sunday may be a decent fair weather day...with at least some
sunshine. Temps will probably start off fairly chilly Sun morning...
likely close to freezing for the valleys. However with ample
sunshine, temps should climb well into the 50s for the lowlands
despite 850 mb temps starting off in the -2 to -4 deg C range Sun
morning.   

Weak low pressure at the tail end of our current cold front is
expected to linger off the California coast through the weekend. Most
models energize this system a little as the Pacific jet noses toward
California Sun night/Mon. An incoming upper trough is expected to
pick up this system and lift it northward, potentially spreading rain
northward into Oregon. Pressure gradients will be easterly through
the Columbia Gorge at that time, and the 12z ECMWF/18z GFS continue
to hint that some low-level cold air may remain dammed up along the
east slopes of the Cascades Mon morning. Luckily current guidance
holds off precipitation in the Columbia Gorge until Mon afternoon,
which would likely see temps well above freezing by the time precip
reaches the ground. Otherwise, expect Monday to bring an increasing
chance for rain from south to north, with snow levels somewhere near
the Cascade passes.  Weagle

.LONG TERM...Monday night through Saturday...Longer range guidance
shows decent agreement in having deep, persistent upper troughing off
the U.S. West Coast, while upper ridging generally dominates the
Rockies. The S-SW flow aloft in between these two features will
likely guide a series of disturbances northward into our region from
the California waters. This will keep our weather unsettled with
showers or periods of rain and snow levels near the Cascade passes
for much of next week. None of these systems are expected to be
particularly strong at this point; but given the current guidance
next week looks fairly damp with near to slightly below normal
temperatures.  Weagle

&&


.AVIATION...A cornucopia of conditions this afternoon with 
rain ahead of a warm front. Most inland sites seeing VFR CIG with
rain but it appears offshore flow near the mouth of the Columbia
River Gorge is keeping that area's terminals VFR. Persistence
appears to be the most likely forecast, at least until the warm
front comes through this evening. Then may see a break in rain
and improvement to MVFR or even VFR for a few hours before MVFR
or IFR conditions develop with moderate rain along the cold front
later tonight and Saturday morning. Look for strong winds out of
the south along the coast this evening with gusts as high as 40 
kt, and breezy conditions out of the south inland tonight with 
gusts as high as about 30 kt.

KPDX AND APPROACHES...Offshore flow appears to be keeping
conditions VFR with light rain. May still see MVFR conditions
develop with more moderate rain starting after 12Z Saturday.
Winds will become gusty out of the south this evening for a few
hours and could see gusts as high as 30 kt in the area. Bowen

&&

.MARINE...Not much change to the forecast this afternoon as the
general trends remain on track. The only real difference is a
shift of peak winds to a little bit later based on current
observations and a timely ASCAT pass around 12:30 pm which showed
the surface low quite well. The main story is a deepening strong
low will approach the waters from the SW this evening, with a 
warm front moving N across our coastal waters. The low will 
deepen to around 1000 mb and make landfall along the northern 
Washington coast around midnight tonight. The associated cold 
front will move through the waters tonight and onshore from N to 
S from around midnight to 4 or 5 am early Saturday. Look for 
brisk E to SE winds to become strong southerly gales as the warm 
front moves N through the waters, then continue until the cold 
front moves onshore later tonight. Will maintain the current Gale
Warnings. Behind the front will be a period of NW winds with 
gusts up to about 25 kt, but easing up by Saturday afternoon. As
high pressure builds in on Saturday and northward on Sunday, we 
will see a bit of N to NE flow on Sunday with a weak thermal 
trough developing along the S Oregon coast. 

Seas still running 6 to 7 ft this afternoon, but will build 
above 10 ft this evening as winds pick up, and peak at 15 to 18 
ft tonight. Seas should drop below 10 ft later Saturday and 
continue below 10 ft into early next week. Bowen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Gale Warning until 2 AM PDT Saturday for Coastal Waters from 
     Cape Shoalwater WA to Cascade Head OR out 60 nm.

     Gale Warning until 5 AM PDT Saturday for Coastal Waters from 
     Cascade Head OR to Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar from 7 PM 
     this evening to 7 AM PDT Saturday.

&&

$$

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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.