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644
FXUS66 KPQR 241742 AAA
AFDPQR

Area Forecast Discussion UPDATED
National Weather Service Portland OR
1040 AM PDT Mon Jun 24 2024

...Morning update, for aviation weather.

.SYNOPSIS...A transient shortwave ridge will bring dry and warm
conditions to the area Monday and Tuesday, warmest on Tuesday. An
upper level trough will then bring relatively cooler temperatures for
Wednesday and Thursday with increasing chances for rain showers. Warm
and dry conditions will return Friday and Saturday with near normal
to slightly above normal temperatures.

&&

.DISCUSSION...MONDAY THROUGH SUNDAY NIGHT...High pressure will bring
seasonably warm and dry conditions to the area Monday and Tuesday,
warmest on Tuesday when a transient upper level ridge will move
eastward into WA/OR. The deterministic NBM has been performing very
well with temperatures over the past several days, and is suggesting
high temps between 75-81 degrees for inland valley locations on
Monday and 84-90 degrees on Tuesday. The probability for high temps
over 90 on Tuesday is at 10-20% from Salem to the Portland metro but
less than 10% elsewhere.

The aforementioned ridge will move eastward into Idaho and western
Montana Tuesday night into Wednesday as an upper level trough
approaches western WA/OR from the northeast Pacific. Models and their
ensembles agree well on the timing of this trough, suggesting the
trough axis will move over the area late Wednesday into Thursday
morning. At the surface, a weak warm front is set to lift northward
over the area late Wednesday, bringing increasing cloud cover and
chances for light rain to southwest WA (20-40% chance) and a 10-20%
chance for most of northwest OR. However, a cold front trailing
behind the warm front will move through Wednesday night/Thursday
morning, bringing higher chances for rain (40-70% chance across
southwest WA and 10-40% for northwest OR with the lowest chances in
the Eugene area). Rain amounts look to stay under 0.1-0.2 inches,
however the wettest model solutions are showing amounts over 0.25
inches. That being said, the probability for 24-hr rain amounts in
excess of 0.25 inches is only 10% or less (except 20-40% over the
south WA/north OR Cascades where moist upslope flow will result in
more frequent/heavier showers).

Behind this system, models and their ensembles are showing another
transient shortwave ridge moving into the region, resulting in
relatively warmer temperatures and dry conditions. Forecast high
temps are currently near normal to slightly above normal for Friday
and Saturday (77-83 degrees for inland valleys, 60s at the coast).
The probability for highs above 90 degrees is less than 10% and there
are no signs of any heat waves on the horizon at this time. If
anything, the forecast trends a bit cooler again Sunday into early
next week with increasing chances for showers. -TK

&&

.AVIATION...
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High pressure remains over the region, with dry mild
southwest flow aloft. This will maintain VFR under mostly clear
skies today through Tuesday. Do still have low level onshore flow
over western WA and far nw Oregon as far south as a KTMK to KSPB
line. This stratus (CIGS 2000 to 3000 ft) will gradually break up
and dissipate through 22Z.

PDX AND APPROACHES...High pressure with mild dry southwest flow
aloft will maintain VFR under clear skies.
-- End Changed Discussion --
 &&

.MARINE...High pressure over the waters today, while thermal low
pressure strengthens over far northwest Calif into far sw Oregon.
This will tighten the northerly pressure gradient enough to
allow north winds to pop 20 to 25 kt gusts Mon afternoon into Mon
evening. But, this mainly over the waters off the central Oregon
coast.

Seas running 2 to 3 ft over guidance, possibly due to the
brief dynamic fetch directed at the Oregon coast Saturday. Seas
are now around 9 to 10 ft at 11 to 12 seconds, so have issued a
Small Craft Advisory for all waters through midday. Rough bar
conditions expected at the Columbia River Bar due elevated seas
and strong ebb current this morning.

Otherwise, not much change in the pattern for early this week,
as high pressure remains anchored off the Pac NW. Low pressure
will arrive mid-week, with a weakening front arriving. This will
bring return of unsettled weather, with return of west to
southwest winds, but still mostly 15 kt or less.   /mh/Rockey

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 10 AM PDT this morning for PZZ210.

     Small Craft Advisory until 2 PM PDT this afternoon for PZZ251-
     271.

     Small Craft Advisory until midnight PDT tonight for PZZ252-253-
     272-273.
&&

$$

www.weather.gov/portland

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