766
FXUS66 KPQR 241025
AFDPQR

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

.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...VFR prevailing with spotty cigs around 5000 ft inland
and 3500 ft north of KTMK on the coast. Various guidance appear a
bit overdone with the MVFR conditions developing at the coast.
HREF forecasting 60-90% chance for MVFR along the coast, but
currently OVC040 at KAST, SKC at KTMK & KONP. Satellite shows
potentially MVFR cigs lurking near KAST so have greater (but not
high) confidence will see MVFR cigs develop there for a several
hours this morning compared to KONP forecast. Will watch satellite
trends over the next couple of hours and see how it matches with
model guidance to create a forecast. For inland sites have high
confidence in the forecast for VFR to prevail. But may see spotty
MVFR SCT-BKN 1500 to 2500 ft along the lower Columbia River for a
few hours this morning.

Low level flow will turn north to northeasterly around 12Z
Monday, then turn back to north to northwesterly by 16Z Monday.
Winds will increase and gust up to 25 kt along the coast and up to
20 kt inland from 17Z Monday to 04-06Z Tuesday.

PDX AND APPROACHES...VFR with broken clouds at 5000 ft, gradually
giving way to mostly clear skies. Will be predominantly VFR
through the TAF period, except for a 10-20% chance of broken MVFR
CIGs between 12Z to 17Z Monday. /mh

&&

.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.
&&

$$

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