874
FXUS66 KPQR 131045
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
345 AM PDT Mon May 13 2024

.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...500 mb analysis depicts a
ridge axis extending from the Great Basin into the northern
Plains while a closed low sits off the California coast and a
shortwave trough sits across the PNW. North/northwesterly
onshore flow continues across the area and is supporting marine
stratus along the coast and into the coastal valleys. Satellite
imagery reveals stratus beginning to develop up through the
Columbia river and a few spots along the Foothills east of the
metro. Model guidance suggests stratus will continue to develop
along the Columbia river and in the northern portion of the
Willamette Valley before dawn. The stratus deck will scatter out
within the valley before noon but may remain in place along the
coast into the afternoon. 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...The weak front that is producing light drizzle along
the coast and moistening up the lower levels of the atmosphere is
slowly shifting inland this morning. While winds will not be
impacted, CIGs are beginning to lower along and behind this front.
The coast is trending towards being stuck in the marine stratus
with IFR CIGs. Inland locations are going to be a bit more
stubborn. Forecasts are showing less of a chance for MVFR CIGs,
with the higher probabilities within Washington north of
KPDX. Likely, this is due to the weak north-northwesterly winds
bringing the marine stratus through the Coast Range gaps. There
is around a 40% chance of IFR CIGs developing along the lower
elevations from KKLS east and from KVUO north.

Through the day, high pressure will once again redevelop with
gusty winds in the forecast along the coast from the north. The
central coast (around KONP and Florence) are likely to be the
strongest areas of northerly winds.

PDX AND APPROACHES...VFR with northerly winds. Breezy conditions
in the afternoon as the front exits and high pressure redevelops.
Around a 60% chance for MVFR CIGs right around sunrise (15-18Z).
-Muessle

&&

.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.

     Small Craft Advisory until 5 AM PDT early this morning for
 PZZ253-273.

&&

$$

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