Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 162141
AFDPQR

Area Forecast Discussion
National Service Portland OR
240 PM PDT Tue Jul 16 2019

.SYNOPSIS...Isolated showers are possible this afternoon and evening
mainly across southwest Washington. A frontal system will produce
more widespread light rain Wednesday through Thursday morning. Drier
and cooler air behind the front will help cool the overnight
temperatures a bit Thursday night. Warmer weather is expected for the
weekend.

&&

.SHORT TERM...Tonight through Friday...Lots of strato-cu across the
region early this afternoon under an upper trough. The interior
valleys should progressively clear this afternoon and evening =, but
onshore winds will likely keep cu over the coast range and the
Cascades. The onshore winds combined with upper support with the
trough from above may provide enough lift over the higher terrain for
isolated showers this afternoon and evening. South winds develop this
evening as a frontal system approaches. This will maintain dewpoint
temperatures in the mid to upper 50s across the area for two more
muggy nights with low temperatures near 60.

A weak warm front will bring light rain to the coast and areas north
overnight tonight into early Wednesday morning. Although the front is
weak, there is a lot of moisture available in the atmosphere as
modeled TPW values are around 1.4 inches. Models indicate there will
be enough isentropic lift ahead of the warm front to increase the
forecast confidence for measurable rain, and have increase PoPs
significantly along the coast and higher terrain of SW Washington and
NW Oregon. A trailing cold front will continue rain chances as it
moves inland Wednesday afternoon and night. Rainfall will be highest
along the coast and higher terrain of SW Washington and extreme north
Oregon where 0.25 to 0.5 inch of rain is possible from Wednesday
morning to Thursday morning. Barely any measurable rain is expected
for the Willamette alley (0 to 0.10 inch), and around 0.05 to 0.15
inch of rain is expected for the coast range and Cascades of central
Oregon.

Drier north flow moves in behind the cold front Thursday afternoon,
which will allow the dew point temperatures to lower to near or below
50 Thursday night, and the minimum temperatures in the 50s. A weak
shortwave trough may generate some drizzle along the coast Friday
morning, but otherwise expect dry weather Friday with clearing in the
afternoon and day time temperatures warming into the upper 70s. ~TJ

.LONG TERM...Friday night through Tuesday...A high pressure ridge
builds over northwest Oregon and Southwest Washington through Sunday
night. This will keep conditions fairly clear and dry through the
weekend. That ridge will start to weaken as a shortwave, associated
with a low in the North Pacific, advances towards the coast. Marine
stratus will fill in along the coast and foothills on Monday. There
is an increased chance of occasional showers on Monday which will
persist through Tuesday. Elsewhere, conditions will remain mostly
sunny.

&&

.AVIATION...Mostly VFR conditions this afternoon and evening.
Radar imagery shows isolated showers developing over the coast
range and areas north of KMMV that may result in occasional and
brief MVFR cigs through this evening. The interior should return
to VFR later this evening after the showers end. South winds
develop tonight along the coast ahead of an approaching front
with gusts possibly around 20 mph as the front moves inland
later in the morning. Low clouds with IFR conditions are likely
along the coast late tonight ahead of the front, and south to
southwest winds may move these low clouds into the south and
central Willamette Valley for MVFR conditions at KEUG and KSLE
Wednesday morning. The rain will move inland Wednesday afternoon
mainly north of KSLE where there will be periods of MVFR
conditions. Any MVFR cigs that develop south of KSLE in the
morning should clear in the afternoon to VFR.

KPDX AND APPROACHES...VFR conditions early this afternoon. Radar
shows isolated showers approaching from the west, that may result
in brief MVFR cigs if any pass over the airport this afternoon
and evening. Cumulus over the Cascade Foothills may back fill
into the north Willamette Valley early Wednesday morning for
possible MVFR cigs at KTTD, KHIO, and KPDX. MVFR Cigs are
possible Wednesday afternoon as a warm front generates light
rain. Winds will be fairly light with the warm front, and there
will not be a shift in wind direction behind it Wednesday
evening, since a cold front follows close behind. ~TJ

&&

.MARINE...The latest 12Z run of the high resolution models have
converged fairly well on the shortwave trough that disturbs the
northwesterly flow associated with the North Pacific High.
Although there are differences in the strength of these wind
speeds most of the models show significant wind speeds that
warrant the issuance of a Small Craft Advisory. Winds will start
shifting into a southwesterly regime tonight. Wind gusts between
21 and 30 kt in the northern waters for most of the day
Wednesday. The southern waters have an advisory for a shorter
time period late Wednesday as these stronger winds are more
isolated to the north. However, this may change if the winds
extend farther south in future model runs.

High pressure begins to rebuild offshore on Thursday and
strengthens for the weekend. This will result in a return to
northerly winds through early next week. Gusts of 25-30 kt can
be expected for the weekend with the strongest winds beyond 10 NM
offshore.

Seas start in the 3 to 4 ft range, then build to around 8 feet
Thursday morning. Seas will be choppy as this system passes with
the potential for square seas on Thursday morning. Seas will
stay above 5 ft through the weekend.The larger seas are a
product of the increased wind wave height from the short wave
system that moves through Wednesday night into Thursday but also
from a 7 ft swell out of the NW that will be the dominant swell
throughout the forecast time period. -BPhillips/mh

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 8 AM to 5 PM PDT Wednesday for
     Coastal Waters from Cape Shoalwater WA to Cascade Head OR
     out 60 NM.

     Small Craft Advisory from 11 AM to 2 PM PDT Wednesday for
     Coastal Waters from Cascade Head OR to Florence OR out 60
     NM.

&&
$$

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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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