Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 250342
Area Forecast Discussion
National Weather Service Portland Oregon
841 PM PDT Mon Oct 24 2016
.SYNOPSIS...A deep low pressure center well off the Washington
coast will gradually weaken and shift north over the next couple of
days. Another low develops well off the Northern California coast
Tuesday night. The warm front lifts north into the area Wednesday
morning. Gusty wind will likely accompany this system along the
coast on late Wednesday. The area will remain under the influence of
a broad upper trough with generally wet and showery weather
throughout the rest of the week and into the weekend.
.SHORT TERM...Tonight through Thursday...A deep surface low pressure
area around 350 nm west of KAST remains nearly stationary this
evening. Frontal boundary was located along the Cascades and
foothills as of 03Z. Satellite and radar also showing isolated
stronger cells over the coastal waters. ENTLN lightning from 02Z to
03Z indicating a cluster of strikes off Curry County in Southwest
The low weakens tonight and Tuesday as it moves to the north. An
occluded front continues to wrap back into the low. Storm force wind
speeds remain well offshore. The east gradient over the coastline
will keep the strongest wind well offshore. The overall gradient
relaxes Tuesday as the upper low heads north. Shower activity has
already diminished along the coast and Willamette Valley. KRTX
dual-pol doppler radar at 03Z showed the heaviest showers along a
line from the South Washington Cascade foothills to the North Oregon
Cascade foothills. Maintained a thunderstorm threat for the coastal
strip through Tuesday morning.
The 00Z NAM indicates precipitation re-developing along the coast
Tuesday morning, but not making it much inland before it falls apart.
There is a pretty good chance that interior valleys and the Cascades
and foothills will have much more dry time Tuesday compared to wet
time. Models are in fair agreement that a surface wave off northern
California will move north and develop into a closed surface low late
Tuesday night and Wednesday morning. This system will send a fairly
strong warm front over the area. Precipitable water values and lift
along the frontal zone are a good indication of a fairly wet warm
frontal passage on Wednesday. This will be followed by the cold front
later Wednesday. Models indicate the cold front could stall, turning
into a mostly stationary front with periods of rain continuing over
western Oregon and Washington overnight then moving east on Thursday.
.LONG TERM...Thursday night through Monday...Wet weather pattern
looks to continue into this weekend, with another trough dropping
out of the Gulf of Alaska Thursday into Friday. May get a brief
break from the rain Friday morning as shortwave ridging builds up
ahead of the next surface Low that comes up from the southwest. This
Low looks fairly weak, bottoming out in the high 990s to right
around 1000 mb. Heavier rain will impact southwest Oregon, but
should be more moderate as it moves farther north into Northwest
Oregon and Southwest Washington. Showers should linger across the
area Saturday night through Sunday morning before another weak
system comes up the same track as the last Low, along the track of
the south side of the upper-level trough sitting off the coast of
Washington and Oregon. This one looks fairly weak as well, only
bringing moderate rainfall to our area Sunday evening through Monday
morning. This second surface low is more associated with the upper-
level trough, which shifts onshore Sunday night into Monday, though
another upper-level trough appears to come in and take its place off
the coast of Washington and Oregon for on-and-off rainy weather to
continue into early next week. -McCoy
.AVIATION...Primarily VFR conditions tonight through Tuesday.
Could see some MVFR CIGS with if any clearing occurs. Winds will
be breezy out of the south to southeast.
KPDX AND APPROACHES...VFR with breezy winds out of the southeast.
.MARINE...A low pressure system currently located off Vancouver
Island will continue to weaken and move north. Gales over the
waters, strongest over the outer waters, will continue into Tue
morning with the winds diminishing in the afternoon. Seas will
peak tonight, ranging from around 20 ft near the coast to 25 ft
over the outer waters.
Another low, a bit weaker, is expected to move north off the OR and
WA coast near 130W Tue night into Wed night. Gale force winds
will be possible with this system, most likely Wed over the outer
PZ...Gale Warning until noon PDT Tuesday for Coastal Waters from
Cape Shoalwater WA to Florence OR out 60 nm.
Small Craft Advisory for Rough Columbia River Bar until 5 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.