Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 292134
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
235 PM PDT Wed Mar 29 2017

.SYNOPSIS...A cold front will move inland tonight with showers
continuing into Thu as an upper level trough of low pressure moves
across the Pacific NW.  Fri is expected to be dry as high pres moves
across the region, then chances for rain return for the weekend as
the next system moves in.

&&

.SHORT TERM...This afternoon through Saturday...Observations this
afternoon place a weak cold front near Astoria, stretching
southwestward to off the southern Oregon coast. Not a ton of rain
associated with the front, but radar shows some light showers north
of Salem. Stratiform rain associated with the earlier warm front is
lingering over the Cascades from about Mt. Jefferson south and will
taper off through the evening hours.

The trailing upper level trough is expected to move across Thu
morning, with moisture generally limited to low levels below about
10k feet. Once the upper trough passes, shower activity is expected
to become more reliant on orographic lift and thus will tend to
become more tied to the upwind side of the mountains.

Thu night into Fri a ridge of high pres at the surface and aloft
pushes east into western Oregon and Washington. Subsidence will
stabilize the atmosphere, bringing an end to the showers. Low levels
will be slow to dry out, though, as offshore flow never really gets
going. Some fog Friday morning seems inevitable given all of the
moisture around, but will depend on low level flow either being very
light, which it should be, or being onshore, which is questionable.
It looks like there may be some offshore drift that prevents fog
along at least the central coast and possibly elsewhere.

The next system approaches Saturday and looks like it will produce
some light rain over the area, mainly in the northwestern portions of
the local forecast area with surface low pressure off Vancouver
Island. However moisture looks fairly limited, so not expecting any
impressive or terribly significant rain. Could even see some sun,
particularly during the morning hours. Bowen

.LONG TERM...Saturday night through Wednesday...Models are in fairly
good agreement through about Monday with a weak upper trough moving
through the area for a continued low chance of showers. After Monday,
though, models diverge, with a wetter system moving into the area
sometime between Tuesday and Thursday. Overall, though, the extended
doesn`t look as wet as the trend has been. Bowen

&&

.AVIATION...MVFR conditions for most TAF sites this afternoon.
Not sure exactly when the MVFR cigs will clear the area. Should
have a better idea in the next few hours as the cold front moves
onshore. Given the wind shift at KAST, expect frontal passage at
most TAF sites in then next 2 to 3 hours. Would expect this cold
front passage to improve cigs and visibility to VFR, especially
given the amount of dry air behind the front (per GOES-16 7.34u
channel). However, shallow moisture in cyclonic flow may be
sufficient enough to continue low cigs/drizzle well into the
overnight hours. Have put the best guess on cigs/visibility going
into the evening, but would not be surprised if lower
cigs/visibility persist.

PDX AND APPROACHES...MVFR conditions will continue through the
evening. Expect the cigs/visibility to improve behind the cold
front, but confidence is not that high in that solution, and MVFR
conditions may continue well into the overnight hours. /Bentley

&&

.MARINE...Using available surface, buoy, and satellite
observations, anticipate frontal passage to be through the
waters and onshore by 00Z. Once this front does pass through,
winds will fall below 20 knots and shift to the west northwest
which should end any small craft for winds concerns. Long period
westerly swell will remain above 10 feet through at least
tomorrow morning, and once it falls below that level it should
remain there until the middle of the weekend. Another 12 to 14
foot long period swell will continue for the second half of the
weekend and into next week, but a lack of any significant surface
fronts or low pressure centers will limit any additional impact
from wind waves. /Bentley

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 5 PM PDT this afternoon
     for Coastal Waters from Cape Shoalwater WA to Florence OR
     out 60 nm.

     Small Craft Advisory for hazardous seas until 5 AM PDT Thursday
     for Coastal Waters from Cape Shoalwater WA to Florence OR
     out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar until 5 AM
     PDT Thursday.

$$

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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.



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