773 
FXUS66 KPQR 010313 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
813 PM PDT Mon Aug 31 2020

Updated aviation discussion...

.SYNOPSIS...A ridge of high pressure will bring very warm and dry 
weather through the rest of the week and into the weekend. 

&&

.SHORT TERM...Tonight through Thursday...A strong ridge of high 
pressure aloft is expected to push into the region from the west 
tonight and Tuesday, then remain over the Pacific Northwest through 
the remainder of the week for dry and warm weather. Model 850 mb 
temperatures Tuesday and Wednesday are expected to reach 18C-20C 
over the inland valleys. The Oregon/California (ORCA) coastal 
thermally induced surface trough is expected to build north up the 
Oregon coast tonight, before shifting inland Tuesday. While the 
trough remains along or near the coast through Tuesday morning, any 
marine diurnal marine clouds will tend to be limited to coastal 
areas, a northeast offshore flow will aid in warming the lower 
atmosphere, while likely also allowing some smoke from the east side 
of the Cascades to drift back west of the crest. Model soundings 
suggest that while the 850 mb temperatures warm quickly in the next 
24 hours due to subsidence, surface temperatures may lag a little, 
so will limit the mention of near 90F temperatures Tuesday to the 
southern half of the Willamette Valley. Similarly on Wednesday, a 
return to a northwest onshore flow will likely keep the lower 
Columbia and northern Willamette Valley in the 80s, while the south 
end of the valley sees little if any cooling with a northerly 
breeze. Higher elevations in the Cascades will tend to remain on the 
warm side through the week above the subsidence inversion. Models 
generally suggest Thursday will be the warmest day in the short term 
as 850 mb temperatures warm to 22c-24C over the interior. Again, 
especially in the north, do not expect the lower atmosphere to fully 
mix out, meaning surface temperatures topping out in the range of 90 
to 95 ought to cover it for inland low elevation valleys Thursday.

.LONG TERM...Thursday night through Monday...The upper ridge is 
generally indicated by models to not just remain over the region 
through the weekend and into early next week, but is likely to 
strengthen some. This will result in an extended period of very warm 
and dry weather. As we are getting into September, it becomes less 
likely to see the lower atmosphere go dry adiabatic up through 850 
mb, so despite seeing model temperatures at 850 mb reaching 22C-26C 
at times, expect surface temperatures at lower elevations to be 
limited to the 90s, with the warmest temperatures over the south 
interior Monday.

&&

.AVIATION...High pressure will persist across the region with dry
northwesterly flow aloft. Expect VFR conditions inland under
mostly clear skies over the next 24 hours. Along the coast IFR 
to LIFR marine stratus is expected to develop after 08Z Tuesday.
It will likely persist through late Tue morning before
dissipating around 18Z to 19Z. Gusty northerly winds will 
redevelop along the coast as well by Tue afternoon as a thermally
induced trough builds northward into the southern Oregon coast. 
At KONP expect gusts around 25 kt to persist through early Tue 
evening.

Refer to http://weather.gov/zse for detailed regional aviation 
weather and hazard information.

KPDX and APPROACHES...VFR conditions are expected over the next
24 hours under mostly clear skies. Generally light northwesterly
winds will increase Tue afternoon and evening to around 10 kt. 
/DDH

&&

.MARINE...Northerly winds will increase this evening as the 
surface pressure gradient tightens over the waters, especially 
over the southern waters where gusts between 20 and 25 kt are 
expected. This will result in steep, choppy seas around 6 to 9
feet with a dominate period of 8 to 10 seconds. Therefore, have 
issued a small craft advisory for winds and seas for zones PZZ275
and PZZ255 starting tonight.

The surface pressure gradient will continue to tighten overnight
enabling small craft northerly winds to spread into zones PZZ270
and PZZ250 by Tuesday morning along with steep choppy seas 6 to 
9 feet with a dominate period of 8 to 10 seconds expected.

Tuesday appears to be the windiest day at this time, with gusts 
increasing to 25 to 30 kt. In addition to the gusty northerly 
winds, seas will through Tuesday and approach 10 ft by the 
Wednesday. Seas remain elevated through Wednesday night before 
falling to around 5 to 7 feet Thursday into Friday. /42 

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 8 AM Tuesday to 2 PM PDT Wednesday 
     for coastal waters from Cape Shoalwater WA to Cascade Head 
     OR out 60 NM.

     Small Craft Advisory from 8 PM this evening to 2 PM PDT 
     Wednesday for coastal waters from Cascade Head OR to 
     Florence OR out 60 NM.

&&

$$

Interact with us via social media: 
www.facebook.com/NWSPortland 
www.twitter.com/NWSPortland