Area Forecast Discussion
Issued by NWS Portland, OR

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689
FXUS66 KPQR 230357
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
857 PM PDT Sat Apr 22 2017

.SYNOPSIS...Showers will decrease tonight, but return Sunday as an
upper level trough moves over the area. A strong Pacific Jest stream
will bring a couple of unseasonal moist fronts to the area Monday
and Tuesday with the potential for occasional gusty winds, and
unseasonal high snow accumulations for the Cascades. Moist onshore
flow will continue showers Wednesday and Thursday.
&&

.SHORT TERM...Tonight through Tuesday...Post-frontal showers have
eased this evening with lingering isolated showers over the higher
terrain of the Cascades and the coast range. The showers will
continue to decrease tonight. Showers will return to NW Oregon and SW
Washington early Sunday morning as an upper level trough begins to
move over the Pacific NW, and continue throughout the day Sunday.
Snow levels will lower down to the Cascade passes by Sunday morning.
Rainfall totals of 0.25-0.75 inch is expected from Sunday morning
through Sunday evening with the higher amounts over the coast range
and the SW Washington Cascades. Locally 1 to 3 inches of snow is
expected at or near 4500 feet. ~TJ

From previous discussion (211 PM Saturday)...
The next system will be the initial system to ride an increasingly
strong Pacific jet stream and zonal or westerly flow into the Pacific
Northwest. Overrunning rain from this system will spread in Sunday
night and Monday morning, changing to showers Monday afternoon.
Amounts from this system could reach 1 to 2 inches in the mountains
and along the coast, with 0.5 to .75 inch in the valleys. Snow levels
will hover near the Cascade passes for this system, and could cause
some travel problems, with significant accumulations possible,
especially at ski resort type elevations. In addition, it could be a
bit breezy along the coast with this system as well.

Showers from the Sunday night and Monday system will continue Monday
night as its trailing upper level system moves through. Rain will be
increasing again Tuesday, especially in the afternoon, as the next
system riding the strong Pacific jet moves in. Snow levels will rise
some Tuesday before falling again after Tuesday. It will be breezy
again especially near the coast Tuesday, but probably inland, too.
Tolleson

.LONG TERM...Tuesday night through Saturday...An occluded front is
forecast to move through southwest Washington and northwest Oregon
Tuesday night for more rain and higher elevation snow. Westerly flow
will keep showers going across the area Wednesday into Friday. Snow
levels will tend to hover around the Cascade passes. The models vary
a bit with the upcoming weekend have some low pops at time in the
early part of the weekend due to the uncertainty. Tolleson
&&

.AVIATION...Expect any lingering post frontal showers to come to
an end later this evening for a period of dry weather overnight.
Conditions will remain predominately VFR tonight, with occasional
MVFR along the coast. A weak front will move across the forecast
area on Sun and bring another round of rain. Expect MVFR cigs to
redevelop along the coast Sun morning and persist through the
day. The interior will likely remain VFR, with occasional periods
of MVFR under heavier showers. Another front is expected to bring
periods of reduced flight conditions Sun night/Mon morning.

KPDX AND APPROACHES...Predominately VFR through Sun morning. Rain
returns after 14Z, with occasional periods of MVFR cigs possible.
Otherwise, conditions remain predominately VFR Sun. /64

&&

.MARINE...Winds and seas have fallen below advisory criteria this
evening so will let the SCA expire at 9 PM. Another weak frontal
system will move across the waters on Sunday, but don`t expect
winds to get back up above 20 kt until the next system Sunday
night into Monday morning. This next system will be a moderately
strong 999 to 1003 mb low that moves into the coast making
landfall around the mouth of the Columbia river. Therefore,
expect the strongest winds with this system to be generally south
of Cape Falcon. There is a chance for gales with this system, if
the low is stronger (999 mb), while the weaker solution (1003
mb) would only generate high-end small craft advisory winds late
Sunday night through Monday morning. Beyond Monday, we stay in an
active pattern with systems every 24 to 48 hours through the end
of the week. We may get a break going into next weekend.

Seas will remain around 8 to 9 feet until the system Sunday night
into Monday which will bring seas generally south of Cape
Falcon up to 10 to 12 feet. After that system seas hover around 7
to 10 feet through early next week. Wednesday models suggest a
decent fetch developing with the low pressure system that moves
toward the coast of British Columbia which brings seas up into
the mid teens. If the ECMWF solution pans out, however, this low
will be weaker and move a bit faster which would result in a
smaller fetch and lower seas, so confidence isn`t very high at
this time. Later in the week if we can get a break in these
systems seas may drop down to 5 to 7 feet on Friday. /64/McCoy

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for Rough Columbia River Bar from 1 AM to
     5 AM PDT Sunday.

     Small Craft Advisory for Rough Columbia River Bar from 1 PM to
     6 PM PDT Sunday.

&&
$$

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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