Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 202126
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
225 PM PDT Mon May 20 2019

.SYNOPSIS...A front will produce rain across NW Oregon tonight and
Tuesday morning. Showers will decrease behind the front Tuesday
morning, but an upper trough will support post-frontal showers in the
afternoon, and possibly a few thunderstorms across Lane County late
in the afternoon. Onshore flow will support deep marine pushes
Tuesday night and Wednesday night. Gradual warming is expected
Wednesday and Thursday with a threat for showers over the Cascades in
the afternoons.

&&

.SHORT TERM...Tonight through Thursday...Showers will pick up this
evening as a surface low currently around 400 miles off of the north
Oregon coast approaches. Satellite imagery shows a fairly well
organized front associated with this low that will begin rain at the
coast early this evening, then rain spreading inland later this
evening and tonight. The best chance for rain is over NW Oregon, with
lower chances for SW Washington.

The rain will decrease from north to south Tuesday morning, but then
reinvigorate over Lane County,and the Oregon Cascades & Coast Range
Tuesday afternoon when the low moves inland. The Cascades, coast and
coast range can expect 0.25 to 0.5 inch of rain this evening through
Tuesday morning with less than 0.25 inch elsewhere, and generally
less than 0.10 inch north of Salem. Thunderstorms are possible in the
afternoon across Lane County where isolated down pours will result in
local additional QPF from 0.10-0.25 inch. Temperatures will be on the
cool side with daytime highs expected to peak in the low to mid 60s.

The showers will decrease Tuesday night as an upper ridge tries to
build over the Pacific NW. A large upper low moving inland across
Western Conus prevents the ridge from fully materializing. Onshore
flow and a fairly deep marine layer will result in marine clouds
moving inland Tuesday night through Wednesday morning. Diffluence
aloft between the upper low and the upper ridge moves over the region
Wednesday afternoon and provides enough instability to support a
chance for afternoon showers across the Cascades.

There will be little change in the pressure pattern Wednesday night
and Thursday and expect a cloudy start to the day Ton Thursday
followed by Cascade showers in the afternoon. Daytime temperatures
will gradually warm Wednesday and Thursday. ~TJ

.LONG TERM...Thursday night through Monday...Dry weather is expected
for Friday as the upper ridge asserts itself over the Pacific NW. The
ridge is not very strong though as upper troughs moving over the
ridge will return a threat for showers for the weekend. The models
are showing these troughs to deepen and form an upper low over NW
Oregon by Saturday for cooler conditions and periods of rain for
Saturday and Sunday. Drier weather is possible on Monday, but expect
showers over the Cascades in the afternoon as the upper low moves
inland and increases the chance for diffluent flow aloft.~TJ
&&

.AVIATION...Generally VFR across the area early this afternoon.
This will hold through at least early evening along the coast
and 06Z to 12Z for the inland TAF sites. There is the potential
for MVFR cigs from KSLE to KEUG 08Z through Tue morning.
Conditions improve from north to south Tue morning as the surface
low pressure area slides southeast into southwest Oregon.

KPDX AND APPROACHES...Expect predominant VFR conditions through
Tue morning. Cigs will be around 040 through early afternoon and
then lift to above 050. There is a chance of MVFR cigs in the 10Z
to 15Z Tue time frame, especially in the Tualatin River Valley.
Weishaar

&&

.MARINE...Weak high pressure remains over the coastal waters into
early afternoon. Latest models in general agreement showing a 995
mb low pres area near 45N 130W at 00Z Tue. Wind speeds have
increased early this afternoon, with gusts to 30 kt at buoy
46089. The 12Z NAM and GFS show 30 kt boundary layer wind speeds
over PZZ275 late this afternoon into the evening. Wind speeds
ease to around 25 kt 03Z-06Z Tue. The NAM is slightly stronger
than the GFS. Not as confident with the gale warning for PZZ275,
but will let it ride since it has already been issued. Solid
small craft advisory level speeds over the waters overnight
through 14Z Tue.

The low looks to be centered just west of buoy 46050 12Z Tue.
Models then take it inland near the Newport jetty by 18Z. Wind
will back to the east late tonight and Tue morning. Small craft
advisory level northwest to north wind develops over the waters
Tue afternoon behind the departing low. This northerly wind
pattern continues through at least Fri.

Wave heights expected to reach 10 ft over PZZ275 by late this
afternoon and then over the remaining waters tonight. Seas
continue to build Tue, generally 11 to 13 ft by the afternoon.
Seas then remain at or slightly above 10 ft Tue night through at
least Wed evening and have issued an advisory for PZZ275 and
extended the existing advisory for the remaining zones through
12Z Wed. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 7 AM PDT Tuesday for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     10 NM.Waters from Cape Shoalwater WA to Cascade Head OR
     from 10 to 60 NM.

     Small Craft Advisory for hazardous seas from 5 PM this
     afternoon to 5 AM PDT Wednesday for Coastal Waters from
     Cape Shoalwater WA to Florence OR out 10 NM.Waters from
     Cape Shoalwater WA to Cascade Head OR from 10 to 60 NM.

     Small Craft Advisory for winds until 5 PM PDT this afternoon
     for Waters from Cascade Head to Florence OR from 10 to 60
     NM.

     Small Craft Advisory for winds from midnight tonight to 7 AM
     PDT Tuesday for Waters from Cascade Head to Florence OR
     from 10 to 60 NM.

     Gale Warning from 5 PM this afternoon to 11 PM PDT this evening
     for Waters from Cascade Head to Florence OR from 10 to 60
     NM.

     Small Craft Advisory for hazardous seas from midnight tonight
     to 5 AM PDT Wednesday for Waters from Cascade Head to
     Florence OR from 10 to 60 NM.

     Small Craft Advisory for Rough Columbia River Bar from 5 AM to
     9 AM PDT Tuesday.

&&
$$

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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 forecast area.


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