523
FXUS66 KPQR 131831 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1131 AM PDT Mon May 13 2024

Updated public and aviation discussions...

.SYNOPSIS...A shortwave trough will move eastward over the
Cascades today, bringing cooler temperatures to the area. Marine
stratus developing west of the Foothills will dissipate across
the Willamette Valley late this morning but may linger along the
coast into the afternoon. High pressure ridging returns
Tuesday-Thursday, continuing warm, dry, and clear conditions.
Uncertainty remains with whether or not this trend continues
over the weekend.

&&

.SHORT TERM...Now through Wednesday...UPDATE: Stratus clouds
within interior valleys and along the central Oregon coast have
dissipated or begun to dissipate. Some lingering marine clouds
remain over the north Oregon and south Washington coastline, and
will likely remain through the afternoon. Otherwise, expect mostly
clear conditions today. The previous discussion continues below.
                                                         -Alviz

The shortwave trough axis will shift east of the Cascades this
morning and northwest flow will develop across the PNW in its wake.
Surface high pressure across the northeast Pacific will shift
northeast toward the WA/OR coast through the day and will continue
to support northerly flow across the region. Highs will be cooler
than yesterday 7-10 degrees within the Willamette Valley topping out
in within a degree or two of 70. Areas along the coast top out in
the upper 50s to low 60s.

A ridge developing over the eastern Pacific will shift toward
the West Coast and will retake control across much of the PNW
Monday night into Tuesday. This will maintain dry conditions and
a warming trend through mid-week. Expect another marine stratus
surge to develop Tuesday morning as onshore flow continues
Highs on Tuesday are expected to increase 5-7 degrees across
the Willamette Valley and generally 3-5 along the coast.
Probabilities of exceeding 75 degrees on Tuesday across the
metro are decent at 60-80% and 20-40% for the central/southern
Willamette. The coast will peak in the mid 60s for most
locations. Highs continue an upward trend for Wednesday back
into the upper 70s to low 80s. A thermal trough develops but
remains confined to southern Oregon and isn`t expected to reach
the Willamette Valley at this time. This will inhibit easterly
offshore flow from developing and therefore highs should remain
more reasonable for this time of year. -Batz

.LONG TERM...Wednesday Night through Sunday...WPC cluster
analyses are in agreement of upper level ridging continuing over
the Pacific Northwest through Thursday. This will maintain dry
and warm conditions under predominately clear skies. Cluster
agreement lessens on Friday as 50% of ensemble members think
we`ll maintain upper level ridging, while the other 50% suggests
more troughing/zonal flow. NBM temps are in the low to mid 70s
Friday and through the weekend however, this could change
depending on how the pattern plays out later in the week. This
uncertainty continues through the weekend. If models trend
toward a troughing/zonal flow pattern, we`ll likely see
temperatures cool and a slight chance (15-24%) of PoPs over
higher terrain. If models trend toward keeping the ridge, then
expect the forecast to maintain warm, dry, and clear conditions.
                                               -Alviz/Batz

&&

.AVIATION...A weak front continues to impact the area, with marine
stratus and light drizzle possible at the coast. Cigs at the coast
are in the process of breaking up, with only northern terminals
(KAST) holding on to cloud cover for a little longer. With daytime
heating, we should return to VFR thresholds by the mid to late
afternoon on Monday (around 22z Mon-02Z Tue).

Further inland, VFR conditions with essentially clear skies continue
throughout the rest of Monday day and night as high pressure
continue to impact the area. Gustier winds will be possible from the
north, with gusts up to 15-25kt possible at most terminals.

Later Monday night, the thermal trough moves inland around 09-15z
Tue, possibly bringing some more marine clouds to the inland
terminals. Currently looking at about a 15-30% chance of MVFR
thresholds at inland terminals. At the coast, combined with a sea
breeze, chances of MVFR conditions is higher, at 70-80%. /JLiu

PDX AND APPROACHES...VFR with northerly winds. Breezy northerly
winds continue as high pressure redevelops behind the front.
Slight chance (30%) for MVFR CIGS around 15z Tue due to the thermal
trough shifting inland, but still predominantly expecting VFR. /JLiu

&&

.MARINE...A weak front is shifting inland this morning producing
light rain over the area. Winds remain northerly, and have hung on
longer than expected in PZZ253 and 273. Have already extended the
Small Craft Advisory, but will continue to track as the high
pressure slowly moves. The northerly winds will intensify as high
pressure builds over the area and a slight thermal trough forms
over the coastline. The northerly winds will be less than 15 kt
from early this morning through this afternoon, but will ramp up
again in the late afternoon. Winds will be from the north at 15 to
20 kt with gusts up to 25 kt. From there, winds will increase
further to 20 to 25 kt with gusts up to 30 kt starting around
sunset on Monday. The winds will start picking up in the inner
waters out to 10 NM, then spread north and west. Have issued
another Small Craft Advisory starting around 1600 through Tuesday.
Will note that if the south-central waters do not ease in regards
to wind, may have to merge those two advisories. If this is the
case, there will still be a lull before the other waters kick in.

In regards to seas, nothing overly remarkable as the primary swell
is from the northwest, and the wind wave from the north. Wind
waves will range from around 4 to 6 feet. Combined seas will be 6
to 8 ft through Tuesday, though conditions ramp up mid-week.
-Muessle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 5 PM PDT
     Tuesday for PZZ251>253-271>273.
&&

$$

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