Rip Current in Washington, February 2, 2018

Area Forecast Discussion
National Weather Service Portland OR
234 PM PST Fri Feb  2 2018

.SYNOPSIS...An upper ridge holds over the northeast Pacific
through early next week. Intermittent weak disturbances moving
across the top of the ridge will maintain a threat for rain into next
week, mainly across the north half of the area. The upper ridge
strengthens and moves closer to the coast Wednesday and Thursday for
slight warming and a brief dry period.

&&

.SHORT TERM...Today through Monday...Water vapor imagery shows an
upper ridge over the NE Pacific with a ridge axis around 150 miles
offshore the Washington and Oregon coast. This offshore position of
the ridge axis allows upper level short wave troughs riding along the
top of the ridge to move south and over the Pacific NW. THis type of
ridge is also known as a "dirty ridge". A series of such upper level
shortwaves will continue periods of rain across the Portland Forecast
area through early next week. Snow levels
will remain above the Cascade passes through Sunday and be between
6000 and 8000 feet, before lowering to around 4500 feet on Monday.

The first shortwave troughs is moving over central Washington early
this afternoon and will move east of the Washington Cascades this
evening. Radar shows a line of light rain associated with this
feature moving north to south across NW Oregon. Rain amounts have
been light with 850mb west winds supporting higher rain amounts for
the terrain due to orographic enhancement.

Another shortwave follows close behind and will bring another round
of light rain to the region Saturday. This shortwave is weaker and
currently less noticeable on water vapor, but there is more moisture
available with nearby subtropical moisture, and the rain amounts will
be slightly higher. Onshore 850mb winds will continue to favor higher
rain totals over the mountains. Expect an additional 0.25 to 0.5 inch
for the higher terrain Saturday morning through Saturday evening with
0.2 to 0.06 inch for the Willamette valley south of Salem, and 0.03
to 0.13 inch for the interior valleys north of Salem. The rain should
turn to showers mainly for the higher terrain Saturday afternoon.

A stronger shortwave trough moves across the NE Pacific Saturday
night and Sunday will result in a brief raising of 500mb heights over
the Pacific NW. The short wave will move inland Sunday, but the
higher heights will steer the heavier rain north of the area. Rain
chances will remain fairly high for SW Washington and extreme NW
Oregon with little to no chance of rain for Lane County and most of
the Willamette Valley. Temperatures will also be warmer on Sunday
with high temperatures for the coast and interior low lands expected
to be in the mid to upper 50s. An additional 0.25-0.5 inch of rain is
possible over the higher terrain north of Salem area from Saturday
night through Sunday afternoon with less than 0.15 inch for the lower
elevations.

Another upper level shortwave trough drops south over the area
Monday continuing showers across the region. This trough will support
cooler air aloft coming over the area and the snow levels will lower
down to the Cascade passes (around 4500 feet). The precipitation
wanes as the snow levels lower though, and do not expect much snow
accumulations at or near the passes. ~TJ

.LONG TERM...Monday night through Friday...Model guidance suggest
that the amplified upper level ridge will remain well offshore Monday
night, with the ridge axis centered near 135W. This will enable some
moisture associated with an embedded shortwave impulse to linger
Monday night into early Tuesday morning. Chances will be best along
the coast, in the Coast Range, and Cascades, with some shadowing
expected for portions of the Willamette Valley. Over the last few
cycles, model guidance has shifted to favor a flatter ridge, so
cannot rule out some light precipitation across the area and have
extended the mention of rain a bit further south as a result. Only
modest moisture is suggested, however, so those areas that see
precipitation should not expect any significant accumulations.

Still expect a slight warming trend into Wednesday and Thursday,
though confidence is slightly lower today in the evolution of the
pattern next week. Leaned the forecast towards the ECMWF and about
half of the GEFS members which would maintain temperatures in the
mid to upper 50s and dry conditions for this time period. However,
the GFS (and a handful of GEFS members), would suggest the ridge
will weaken and shift enough to allow a much stronger shortwave
trough to move into the Pacific NW by late Thursday. As a result of
this lower confidence, have cut back a few degrees from the forecast
afternoon highs and also increased cloud cover late Thursday and
into early Friday.   Cullen
&&

.AVIATION...A weak front crossing the region will destabilize the
lower atmosphere a bit and bring predominantly VFR conditions
with only brief MVFR conditions to interior sites late this
afternoon and early this evening. It appears coastal taf sites
are likely to remain stuck in IFR to LIFR conditions for much of
the next 24 hours. Warm advection ahead of another front pushing
into the area late tonight should result in conditions deteriorating
more solidly into MVFR thresholds for interior taf sites towards
12z Saturday.

PDX AND APPROACHES...A slightly unstable lower atmosphere should
result in predominantly VFR conditions with only occasional MVFR
conditions through at least early this evening. Moist onshore
flow and a stabilizing lower atmosphere should lead to a
deterioration of flight conditions into more solid MVFR
thresholds towards 12z Saturday. /Neuman

&&

.MARINE...High pressure will more or less continue over the
northeast Pacific for much of the next week and bring relatively
benign weather to the waters. With that said, weak fronts will
periodically drop southeastward over the top of the ridge of high
pressure and bring brief spikes in gusty winds across mainly the
northern waters. One such front is currently exiting the waters
and pushing inland and another front will likely arrive late
tonight. We may eventually enter a more summer-like northerly
wind pattern next week with the strongest winds shifting to the
waters off the central Oregon coast. A larger westerly swell
still looks on track to bring seas near 10 ft on Monday despite
winds staying relatively subdued during that time. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 3 PM PST this afternoon
     for Coastal Waters from Cape Shoalwater WA to Cascade Head
     OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar from 4 PM
     this afternoon to 8 PM PST this evening.
&&

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the CWA or forecast area.