848 
FXUS66 KPQR 060509 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1008 PM PDT Sun Sep 5 2021

.SYNOPSIS...Warm and dry weather will continue early in the week as 
upper level ridging builds across the Pacific Northwest. A series of 
weak storm systems will bring cooler temperatures and a chance for 
some light rain beginning Tuesday night.  

&&

.SHORT TERM...Tonight through Tuesday night...Water vapor satellite 
imagery this evening shows an upper level ridge centered over 
California building northward. High pressure will continue to build
across the Great Basin as the upper ridge expands further north
across the Pacific Northwest Monday and amplifies into western Canada
Tuesday. 850 mb temperatures will warm to around 17-18C tomorrow,
allowing for surface temperatures to warm well into the 80s, once
again, across the Willamette Valley and Columbia Gorge on Monday.
Further warming of 850 mb temps, to around 21-22C, will allow high
temperatures to likely (~60-80% chance) top 90F on Tuesday.   

A cutoff low currently off the southern California coast could bring 
a few showers to our area Tuesday night. Models are in 
good agreement this low will eject northeastward as an open wave and 
move across the Pacific NW Tuesday night. Model guidance also
suggests the main upper level PV anomaly will shift northeastward
across our northern CWA late Tuesday night. Model soundings still do
not appear favorable for deep elevated convection Tuesday night, but
cannot rule out a rumble of thunder, particularly across southwest
Washington. 

Onshore flow has kept much of the haze and smoke east of the region. 
However, smoke will continue to persist in the immediate vicinity of 
ongoing wildfires in the Cascades over the next few days. Light 
offshore flow, especially Tuesday morning, could allow some smoke to 
drain into parts of the southern and central Willamette Valley, but 
stronger onshore flow should return by Tuesday afternoon. /DDH

&&

.LONG TERM...Wednesday through Sunday...A shortwave trough over the 
eastern Pacific will shift eastward on Wednesday, although latest 
model guidance holds the upper trough offshore until possibly 
Thursday afternoon. This likely means temperatures will cool, but 
still are likely to remain near or slightly above normal through the 
middle of the week. Temperatures should generally continue to trend 
cooler through the end of the week and into the weekend. Onshore 
flow will likely result in temperatures near to slightly below 
average as we inch closer to autumn. General troughing pattern along 
with possible shortwaves moving across the region could result in a 
few light showers at some point during this time as well, but PoPs 
have been held in the 10-20% range per NBM guidance. /DDH

&&

.AVIATION...Onshore flow will continue over the next 24 hours.
Expect LIFR to IFR cigs/visibilities along the coast tonight
before marine stratus begins to scatter out between 16-18Z
Monday morning. There is to potential for low stratus and fog to
clear out at KONP as soon as 12Z, as high resolution model 
guidance does suggest surface winds will temporarily go easterly
between 12-16Z before turning onshore again. That said, confidence
that the light east wind will materialize is low, and the latest
HREF guidance contradicts this by suggesting low stratus will 
hold strong at KONP through 16Z.

In addition to the stratus along the coast, satellite 
observations from 0445Z Monday showed VFR cigs beginning to 
develop along the north OR/south WA Cascade foothills. This area 
of cloud cover may backbuild into the northern Willamette Valley 
after 06Z Monday, but it appears cigs would most likely stay 
above 4000 feet. High-end MVFR cigs cannot be completely ruled
out though. This area of cloud cover should scatter out towards 
16Z Monday.

For detailed regional Pac NW aviation weather information, go 
online to: 
https://weather.gov/zse

KPDX AND APPROACHES...Expect mainly VFR flight conditions to
continue through 06Z Tuesday. Could see a period of high-end 
MVFR cigs between 06-16Z Monday, but it appears cigs will be 
around 4000 feet or higher. -TK

&&

.MARINE...High pressure builds over the waters tonight and into
Monday, this will result in more northerly flow across all 
waters through the start of the week. As the upper level high 
pressure builds a thermally induced trough forms along the 
surface. This will bring northerly winds around 10 to 15 kt with 
gusts up to 20 kt throughout all of the waters by tonight. The 
thermally induced trough will strengthen through Monday morning, 
which will cause winds to rising to 15 to 20 kt with gusts up to 
25 by late Monday morning. Therefore have issued a Small Craft 
Advisory for all zones. The SCA for zones PZZ270 and PZZ275 start
late Monday morning, then these SCA winds extend into zones 
PZZ250 and PZZ255 Monday afternoon. A similar pattern, but 
weaker, is expected Tuesday, with light and variable winds 
returning Wednesday. 

General seas will generally remain northwesterly around 5 to 7 
ft with a 9 to 11 second period through Tuesday. Seas will once 
again start ease toward 4 to 6ft on Wednesday through the 
remainder of the week. /42 

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 8 AM Monday to 5 AM PDT Tuesday for 
     coastal waters from Cape Shoalwater WA to Florence OR from 
     10 to 60 NM.

     Small Craft Advisory from 2 PM Monday to 2 AM PDT Tuesday for 
     coastal waters from Cape Shoalwater WA to Florence OR out 
     10 NM.

     Small Craft Advisory from 3 AM to 6 AM PDT Monday for Columbia 
     River Bar.

&&

$$