461
FXUS66 KPQR 020404 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
905 PM PDT Mon Jul 1 2024

Updated aviation discussion

.SYNOPSIS...Seasonable temperatures will continue through Wednesday
as onshore flow continues. A very strong upper level ridge will then
begin amplifying and moving into the Pacific Northwest beginning on
the 4th of July, peaking in strength July 5-7. Confidence has
increased for a significant heatwave during that time as the
probability for high temps over 100 degrees has increased
dramatically to 60-80% across the interior lowlands.

&&

.SHORT TERM...Monday night through Wednesday night...The short term
forecast is highlighted by an onshore flow pattern with varying
degrees of morning cloud cover, afternoon sunshine, and seasonable
temperatures. In fact, Tuesday is shaping up to be slightly cooler
with high temps generally in the mid to upper 70s across the interior
lowlands and 60s at the coast. Wednesday looks to feature similar
temperatures, albeit a few degrees warmer. As has been the case over
the past several days, northerly to northwesterly surface winds will
increase a bit in the afternoon each day, especially across the
southern Willamette Valley where winds will likely gust up to 20 mph.
This includes the Eugene-Springfield area. Overnight lows each night
look to range between 45-55 degrees, warmest over the Portland metro.
This will offer excellent overnight relief for those without air
conditioning. However, this relief will be short-lived as a
significant heatwave is expected to impact the region from July 4-7,
and possibly even beyond July 7th. This heatwave is discussed in more
detail below.  -TK

&&

.LONG TERM...Thursday through Sunday night...The long term forecast
is highlighted by a significant heatwave with record breaking
temperatures now likely to occur. HeatRisk is now in the moderate to
major category across all of northwest Oregon and southwest
Washington, except for the coast where weak onshore flow looks to
maintain much cooler temperatures when compared to inland locations.
Before getting into the temperature forecast, would first like to
discuss the synoptic scale setup in place. Models and their ensembles
are now honed in on an upper level ridge amplifying over the western
CONUS July 4-7, peaking in strength July 5-7. It appears an omega
blocking pattern will develop during that time due to a closed upper
level low over the northeast Pacific and another over the Northern
Plains into the Great Lakes region. These two lows will help keep the
ridge over the western CONUS locked in place for at least three to
four days, potentially even longer than that.

With this impressive ridge in place, temperatures will become
abnormally hot with record breaking high temperatures now likely to
occur. The latest suite of model guidance continues trending warmer,
with widespread high temps in the lower 100s for most valley
locations away from the coast likely by July 5-6 according to the
deterministic NBM. In fact, the probability for high temperatures
above 100 degrees has increased dramatically to 60-80%. The warmest
ensemble members from the EPS/GEFS suggest high temps close to 110
degrees or warmer, and the NBM is now showing a 15-30% chance for
high temps of 110 degrees or warmer. Regardless of whether high temps
wind up near 100, 105, or 110, it will be more than hot enough for
people to suffer from heat exhaustion or heat stroke if outdoors for
a prolonged period of time, or for people who are indoors with no air
conditioning. This has helped push HeatRisk into the major category
for the entire Portland metro, Salem, Eugene, Columbia River Gorge
and Upper Hood River Valley. A major HeatRisk means anyone without
effective cooling and/or adequate hydration will be impacted,
especially those who are particularly sensitive to heat. Be sure to
do everything you can to stay cool during the upcoming heatwave, and
don`t forget to check on your neighbors and loved ones from time to
time. Lastly, never leave pets or people inside a hot car, and ensure
your pets stay cool during this heatwave as well. Walking your dog in
the afternoon will not be a good idea as their paws may easily burn.
It`s also worth mentioning that overnight lows are looking quite warm
with minimal overnight relief. As of right now, overnight lows will
likely wind up in mid 60s to lower 70s.  -TK

&&

.AVIATION...High pressure will persist across the region with
increasing northwest flow aloft. Onshore flow expected to maintain
marine stratus at the coast with predominately MVFR cigs, although
a 20% chance of IFR through 18Z Tue. Predominately VFR inland
through the period, with the exception for increasing chances of
MVFR CIGS developing by 12-14Z Tue and persisting through 18Z Tue
as morning clouds build. Highest chances (50-70%) along the
Columbia River. Northwest winds expected to increase by Tue
afternoon with gusts up to 20-25 kt.

PDX AND APPROACHES...Predominately VFR expected. However,
backbuilding clouds off the Cascades could (40-70% chance) bring
MVFR cigs to PDX and TTD between 12-18Z Tuesday morning. Northwest
winds around 10-12 kt expected to ease overnight to around 4-6 kt.
/DH

&&

.MARINE...Weak high pressure over the northeast Pacific with lower
surface pressure over California and the Great Basin will persist
through the week. NNW winds across all waters as high pressure
strengthen. Winds will generally peak in the afternoon and
evening hours each day with gusts up to 25 kt. Therefore, have
adjusted the current Small Craft Advisory to now include all
waters. Because the thermal surface low will strengthen through
the middle of the week, will likely see (75%-90% probability)
northerly wind gusts up to 30 kt for zones PZZ272, 273, 252 and
253 by the middle of the week. In addition to the elevated winds,
seas will become more wind driven and build towards 7 to 9 ft by
tonight and look to hold there through the week. /42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Excessive Heat Watch from Thursday afternoon through Sunday
     evening for ORZ104>125.

WA...Excessive Heat Watch from Thursday afternoon through Sunday
     evening for WAZ202>210.

PZ...Small Craft Advisory until 11 PM PDT Tuesday for PZZ251>253-
     271>273.
&&


$$

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