487
FXUS66 KPQR 011731 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1031 AM PDT Mon Jul 1 2024

.SYNOPSIS...Offshore flow slowly decays as a strengthening ridge
of high pressure develops over the Pacific. This pervasive high
pressure will cause temperatures to increase significantly
through the end of the week.

&&

.SHORT TERM...Now through Wednesday...The shortwave trough that
brought cloudy skies and drizzle over the last few days will continue
to shift inland through the day. It will generally shift east of the
Cascades by this late afternoon. Once that trough exits, high
pressure will begin to slowly build in. We will see steady warming
and clear skies over the next week or so, so if you like warm
temperatures...this forecast is for you! The ridge will really
amplify on Wednesday night. Overall sensible weather wise, not
looking at anything overly impactful other than the fog this morning.


Will note that with these dry conditions incoming, will see a
steady decline of humidity, especially east of the Coast Range.
Models have struggled with the areas that sit within the
subsidence inversion around 3000 ft and above so have manually
edited to lower the RH in those areas.
  -Muessle


.LONG TERM...Thursday through Sunday...The longer term forecast
is really where the weather is occurring...though it isn`t
necessarily active weather. The main threat in the forecast, and
where the most time has been spent, is in regards to
temperatures. The synoptic pattern shows a strengthening ridge
forming with a thermally induced trough forming right along the
coastline. This ridge will continue to amplify through the
weekend. But what does this mean for us? Models are showing a
steading warming trend which will lead into several days of more
intense heat. In order to capture an overall view will not
necessarily dive into each day directly.

Friday and Saturday look to be the warmest days of the coming
week which coincides with our general trend of "summer starts
on July 5th". The thermal trough will be quite deep at this
point which will cause winds to be northeasterly at the upper
levels, but more northerly at the lower elevations. They will be
slightly elevated which will help mix down some of the warm air
aloft. At 850 mb (5000 ft AGL) temperatures are forecast to
range from 20-25 deg C (70-75 deg F). Even further aloft at 500
mb (18,000 ft AGL), temperatures range from -7 to -3 deg C
(20-25 deg F). While these temperatures may not seem as
impressive, given their elevation and what we typically see,
they are trending on the warmer side. When we see this pattern,
it confirms that we are looking at hotter than normal
temperatures. In fact, if we look at the "Extreme Forecast
Index", we are on the higher end of what is climatologically
normal, with this being mainly the case from Salem southward.

At this time, there is still a lack of confidence in just how
warm those temperatures will be though. In Eugene, the global
models are showing a fairly narrow spread in high temperatures
for Friday and Saturday. The 25th-75th percentile (most likely
range) shows only a 5 degree spread in the low 90s on Friday,
and around a 10 degree spread on Saturday. The NBM on the other
hand too has a 5 degree spread, but in the upper 90s to up to
105 degrees with little change on Saturday. So what does that
mean forecast wise? At this point, confidence is still quite low
in regards to whether we will see extreme heat. Based on the
global models, there is a 30% chance of exceeding 100 degrees on
Saturday, and the NBM is closer to 50%. There is high confidence
that conditions will be hot...hotter than what we have seen thus
far this year. But confidence is low in regards to whether or
not we will see extreme heat. Luckily we will see some reprieve
overnight as lows dip near 60 degrees in the areas that will see
the highest daytime heating.
  -Muessle


&&

.AVIATION...Marine stratus continues to linger with IFR/MVFR
conditions on the coast, and these lowered conditions are expected
to slowly push offshore/scour out through 20Z Monday. These
conditions are expected to return (50-80% probability) to the
coast around 04Z-07Z Tuesday as a marine push is expected.

Inland locations currently are seeing widespread VFR, with a few
exceptions as MVFR conditions are currently impacting areas north
of KSPB. Locations with lowered flight conditions are expected to
improve to VFR around 20Z Monday. VFR conditions expected to
dominant for inland locations through the remainder of the TAF
period, with the exception of areas north of KSPB as a renewed
marine push, could result in MVFR conditions along portions of the
Columbia River. Could also see some backbuilding clouds off the
Cascades, that could bring MVFR conditions (45%-65% probability)
to KPDX and KTTD starting around 10Z Tuesday.

Inland locations will also likely see northerly gusts up to 20 kt
starting around 02Z Tuesday through 07Z Tuesday.

PDX AND APPROACHES...MVFR conditions will improve to VFR through
19Z Monday. Northerly gusts up to 20 kt starting around 02Z
Tuesday through 07Z Tuesday. Backbuilding clouds off the
Cascades, that could bring MVFR conditions (45%-65% probability)
to KPDX starting around 12Z Tuesday. /42

&&

.MARINE...Weak high pressure over the northeast Pacific with lower
surface pressure over California and the Great Basin will more or
less continue through the week. A weak front is in the process of
passing through, but effects look fairly minimal, with light
northwesterly winds through Monday morning.  Afterwards, expect
NNW winds across the waters as high pressure strengthens toward
the middle of next week, with the strongest winds generally off
the central coast of Oregon and lighter winds farther north. Winds
will generally peak in the afternoon and evening hours each day.
Small Craft Advisory remains on track for the central zones, but
zones further to the north still look fairly marginal. Because as
a thermal low develops along the northern California/southwest
Oregon coast on Tuesday and strengthening/spreading north into
Wednesday and thereafter. As a result will see an increase the
pressure gradient along the coast and over the waters with a >90%
chance that northerly wind gusts of 20-30 kt spread northward
across the waters by mid week. This will in return develop steep
wind driven seas of 5-8 ft with a dominant period of 7-8 seconds
by late Tuesday or Wednesday.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT
     Wednesday for PZZ253-273.
&&


$$

www.weather.gov/portland

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