165 
FXUS66 KPQR 251020
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
318 AM PDT Fri Jun 25 2021

...UNPRECEDENTED HEAT WAVE EXPECTED THIS WEEKEND INTO NEXT WEEK...

.SYNOPSIS...An anomalously strong high pressure system aloft will
move into the Pacific Northwest region over the weekend and into
early next week to bring a stretch of hot and dry weather, likely
breaking several temperature records. An upper low will travel
northward off the coast to bring a slow cool down to the region
through next week, but temperatures will remain 10 to 20 degrees
warmer than average for late June and early July.

&&

.SHORT TERM...Today through Sunday...Not much has changed in the
forecast overnight, still will be very hot into early next week. 
Water vapor satellite loop shows the upper level high pressure moving
onshore over the western B.C. The upper high  pressure will build and
very slowly shift east through the weekend as it is part of an omega
blocking pattern.  The upper high continues to strengthen and move
further inland over the Pacific Northwest Saturday, allowing for even
warmer air to be generated.  Will see inland highs on Saturday around
20F over Thu highs and 10F over todays forecast high.  This
translates to dangerously hot temperatures in the 100-105 degree
range.	Add to that another hot day Sunday with highs inland in the
105-110F range. Temperatures this hot will break June records and
even some all time records.  Good thing about this hot airmass is
that humidity will be low where heat index values will be very
similar to the actual temperature.		       

One change to the forecast/warnings is to add the south WA and north
OR coastal zones to the excessive heat warning for Sunday. On Sunday
that area will see light offshore flow develop pushing much of the
cooler marine layer closer to the beaches. The immediate coast should
remain in the 80s but further inland will see mid to upper 90s. Right
now it appears much of the coast will see onshore flow return Sunday
night into Monday bringing a shallow marine layer for cooler
temperatures.	/mh

	  
.LONG TERM...Sunday night through Thursday...Not much change to the
extended.  Another hot night is expected Sunday night, once again
with readings close to our average high this time of year. The one
exception will be over the far southwestern part of the forecast area
as a part of the thermal trough is expected to split off and head out
over the ocean, with onshore flow around the southern end of it to
bring cooler temperatures, and a return to some marine stratus,
likely south of Tillamook. An upper low will be moving north offshore
of Oregon Monday and will shove the upper high to the east slightly,
to back down the highs a few degrees.  So while not as hot as Sunday,
readings will still be over the 100 degree mark and dangerously hot,
so the Excessive Heat Warning will continue through Monday.

The upper high will move slightly more east and become positively
tilted Tuesday through Thursday, with southwesterly flow aloft
expected for the forecast area. The thermal trough is expected to
move into eastern Oregon, allowing for some relief in temperatures,
yet readings will stay 10 to 20 degrees above normal for this time of
year.  Little pieces of energy rotating around the high pressure and
some moisture moving in may be allow for some convection to begin
again over the high terrain for next week.
/Kriederman

&&

.AVIATION...12Z TAF Preliminary thoughts: Closed high pressure
roughly centered over Vancouver Island is swinging cirrus across
the PacNW under northeasterly flow. This cirrus is broken enough
to allow periodic peaks at the coastal stratus slowly pushing up
the Columbia River. In general, the sinking motion under the 
upper high is compressing the coastal stratus into a shallower 
layer which has resulted in IFR/LIFR cigs at the coast. This same
sinking has also limited the interior spilling over the coast 
range as compared to previous nights. That said, still expect to 
see some morning low clouds around the PDX Metro region, mainly 
affecting KPDX and KTTD TAFs. Am not seeing as much intrusion up 
the Umpqua drainage to the south but say still get some clouds 
around KEUG for a while this morning as well. Any inland clouds 
should dissipate fairly quickly. Again expect the coastal clouds 
to pull west to just offshore around midday. The stratus will 
return over the coastal terminals this evening but north to 
northeast flow at the lower levels will keep clouds at bay longer
to the north near KAST.

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

KPDX AND APPROACHES...Expect few-sct low clouds in the vicinity
of the terminal this morning. They should dissipate around 16Z 
or so. VFR conds expected thereafter through at least 26/12Z.
/JBonk 

&&

.MARINE...No immediate concerns as northerly flow will continue
over the waters for the next couple days. Developing surface low
pressure over the waters with a nearshore southerly wind 
reversal Sunday evening has some weather model support for SCA 
level wind gusts around 25 kt Sunday night and Monday, but this 
is about a 60% probability at this time. For the outer waters, 
longer fetch northwesterly winds may result in a building swell 
and steep seas to 8 feet also possibly warranting an advisory 
statement for Tuesday and Wednesday. /JBonk

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning from 10 AM Saturday to 11 PM PDT Monday 
     for Cascade Foothills in Lane County-Cascades in Lane 
     County-Central Coast Range of Western Oregon-Central 
     Columbia River Gorge-Central Willamette Valley-Coast Range 
     of Northwest Oregon-Greater Portland Metro Area-Lower 
     Columbia-Northern Oregon Cascade Foothills-Northern Oregon 
     Cascades-South Willamette Valley-Upper Hood River Valley-
     Western Columbia River Gorge.

     Excessive Heat Warning from 11 AM to 9 PM PDT Sunday for North 
     Oregon Coast.

WA...Excessive Heat Warning from 10 AM Saturday to 11 PM PDT Monday 
     for Central Columbia River Gorge-Greater Vancouver Area-I-
     5 Corridor in Cowlitz County-South Washington Cascade 
     Foothills-South Washington Cascades-Western Columbia River 
     Gorge-Willapa Hills.

     Excessive Heat Warning from 11 AM to 9 PM PDT Sunday for South 
     Washington Coast.

PZ...None.

&&

$$

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