Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 112121

Area Forecast Discussion
National Weather Service Portland OR
221 PM PDT Tue Aug 11 2020

.SYNOPSIS...A broad upper level trough continues to swing across the
Pacific Northwest through Wednesday. This will bring cooler
temperatures along with an increase in cloud cover from tonight into
the morning for areas along the coast and the northern part of the
Willamette Valley. Warmer weather returns Friday and into the weekend
as an upper level ridge builds over the northwest.


.SHORT TERM...Tonight through Thursday...A broad upper level trough
continues to move across the Pacific NW through Wednesday. This upper
level trough will continue to usher in cooler temperatures and
increasing cloud cover during the overnight hours and into the
morning. However, as the latter part of the week approaches, an upper
level ridge starts to develop across the Pacific NW. In addition to
this upper level ridge, a thermally induced low along the
Oregon/California border starts to develop on Thursday. The
Oregon/California (ORCA) low along the southern part of the CWA, in
conjunction with the upper level ridge towards the north, will be the
major synoptic features going into the weekend, which will cause a
warm and dry pattern to develop through the latter part of this week.

Temperatures will remain on the cool side through Thursday. Highs in
the low to mid 70s inland and low to mid 60s along the coast
Wednesday. High temperatures will warm into the upper 70s and lower
80s inland and low to upper 60s along the coast Thursday. /42

.LONG TERM...Thursday night through Monday...Models are in good
agreement in showing an upper level ridge along with the ORCA low
developing over the northern and southern parts of the region
respectfully into the weekend, before shifting slowly east early next

Models are showing 850 mb temperatures between 22C to 26C, which is a
good indicator for mid to upper 90s for inland areas from Friday into
Monday. Current model runs are showing the hottest temperatures will
be on Saturday and Sunday, with Sunday possibly seeing 100F
temperatures in the Willamette Valley. Onshore winds through the
weekend should mitigate the temperatures along the coast.

Sunday and Monday models, are showing a shift in the upper level
flow pattern to a more south-southwest as the overall synoptic
pattern shifts east. Also, something to note is that the cause of
the shift eastward looks to be a low off the coast of central
California, which models are suggesting will have what remains of
Hurricane Elida. Elida is currently a Category 2 hurricane that is
expected to weaken rapidly tonight per the Central Pacific Hurricane
Center. This instability within Hurricane Elida, along with the
overall south-southwest upper level flow could increase the chances
for convection over the Cascades by Monday. Therefore, will limit
PoPs to a slight chance for showers in the north Sunday night and
Monday, but the pattern may ultimately be more supportive of
convection over the Cascades. /42


.AVIATION...Clear skies over most of the CWA with the exception
of southwest Washington. VFR is expected to continue inland over
the next 24 hours as weak high pressure aloft continues. Breezy
conditions in the late afternoon are expected as a surface low
pressure to the south starts to build.

Along the northern coast, winds are expected to shift slightly
onshore around 05Z which will push marine stratus against the
west slopes of the Willapa hills. KAST should expect MVFR
ceilings between 05Z and 10Z. Favorable conditions for fog/low
stratus development at KONP between 09Z and 12Z. Ceilings will
likely be around 003.

KPDX and APPROACHES...VFR conditions to prevail for the next 24
hours, breezy conditions in the late afternoon. -BPhillips


.MARINE...The North Pacific high will continue to have a weak
influence over the region keeping a north, northwesterly wind
pattern through the week. A weak disturbance originating near
45N, 140W will move east towards the Oregon Coast tonight and
into tomorrow. At this time, models are showing it move south
rather quickly and by Wednesday morning it has veered off course
toward buoy 46405. If it holds a more eastward trajectory, this
disturbance has the potential to impact our waters by increasing
winds to SCA criteria over night.

To the north, the Georgia Strait low will continue to produce a
fresh northwesterly swell that will be reinforced by the
northwesterly winds within the the North Pacific high. Swell
heights are expected to be 8 to 9 ft, at around 11 sec. To the
south, a surface low over the Oregon, California border (ORCA
low) will begin to spin up Thursday afternoon as a thermally
induced trough driven by diurnal heating. SCA winds are likely in
the central waters beginning Thursday and lasting through the
weekend. Seas will subside by Wednesday afternoon and will trend
between 4 and 6 ft through the week. -BPhillips





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