657
FXUS66 KPQR 050417
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
917 PM PDT Fri Oct 4 2024

.SYNOPSIS...A fast moving cold front continues to push through
the area just over the Cascades, bringing post-frontal showers
until late tonight. Clouds will clear thereafter, resulting in
fog and low clouds until Saturday morning. High pressure will
build through the weekend, bringing mild days with cool nights
Saturday through Monday. Following, gradually cooling and
increasing chance of precipitation through next week.

&&

.SHORT TERM...(Today through Sunday)...Narrow and fast moving
upper trough continues to move eastward over the Cascades,
leaving behind post-frontal showers. As of 3PM Friday, the coast
and coast range has received 0.50in to 0.75in of rain
accumulation, with 0.25in to 0.50in from the interior valley to
the Cascades. Expect a few more hours of rainfall over the
Cascades to increase the total accumulation to near 0.75in. Only
exception are for the areas south of Santiam Pass and Salem,
with only rain accumulation around 0.10in to 0.25in. Snow levels
continue to lower towards 5-6K ft as the front passes, which
could bring a few inches of snow to high elevated areas.

With clouds and showers expected to clear out by this evening,
overnight temperatures are expected to fall back into the upper
30s to mid 40s. These temperatures paired with wet ground and
light winds, fog and low clouds are expected to form tonight and
linger until tomorrow morning. Considering the time of year,
dense fog may be possible down the I-5 corridor and into the
valleys of the Coast Range and Willapa Hills. For the Upper Hood
River Valley, fog/low cloud development is less likely,
resulting in colder temperatures around 34F to 38F. Meeting the
criteria for potential frost, a Frost Advisory has been issued
from 2AM to 9AM Saturday for the Upper Hood River Valley, with
areas around Parkdale and Dee Flat expected to experience the
coldest temperatures.

Saturday and Sunday, low level flow will turn more northerly to
northeasterly, maintaining mild afternoon temperatures. Inland
will be a bit warmer compared to today, so fog/low clouds will
be less likely. Overnight temps are expected to trend warmer,
sitting in the upper 30s to low 40s Saturday night and low to
mid 40s Sunday night. ~Hall


.LONG TERM...(Monday through Thursday)...High pressure is
expected to build back over the region this weekend and into
early next week, resulting in seasonable and dry conditions
through Monday. Cluster analysis and model ensembles indicate
there is around a 40% chance that the next frontal system brings
rain back to the area by Tuesday night into Wednesday and the
other 60% suggesting rain late Wednesday. Uncertainty in timing
and details of the forecast continues through late next week,
but overall upper level pattern remains fairly consistent with
troughing to the west over the Pacific and ridging to the east
over the Rockies, leaving the Pacific NW under southwest flow.
~Hall/DH

&&

.AVIATION...Dry weather has returned to the region with VFR
conditions for most areas. However, concern quickly shifts to
stratus and fog formation due to light winds, clearing skies, and
ample surface moisture. Along the coast, expecting MVFR/IFR
ceilings from around 06-12z Saturday. Inland, moderate to high
confidence (70-90%) for fog formation (locally <0.5 mile vis) for
the Willamette Valley south of the Portland Metro area beginning
05-09z Saturday, with slightly lower confidence (50-60%) PDX and
north along the SW Washington I-5 corridor beginning around
12-14z. Fog that develops is expected to dissipate by 16-19z. VFR
conditions will then prevail under mostly clear skies and light
northerly winds less than 10 kts throughout the area.

PDX APPROACHES...A brief period of VFR conditions continues
through around 08-12z Saturday. Stratus and fog formation becomes
a significant concern after this, although confidence in fog
formation is moderate (50-60%) at PDX locally. Currently thinking
MVFR/IFR stratus could form between 08-12z Saturday, with fog
developing after 12z, dissipating by 17-19z. VFR conditions and
dry weather expected after this. -Batz/HEC

&&

.MARINE...With the passage of a cold front earlier today,
conditions are expected to remain rather benign into next week.
Winds are beginning to turn more westerly behind the front which
is evident in obs from bouy 46041 off of Cape Elizabeth, WA.
Winds near bouy 46029 are southwesterly while 46050 remains
southerly, both of which will eventually be westerly this
evening. Seas across PZZ271 have underperformed, generally 4-6
feet when seas around 10 feet were expected. Due to lower wave
heights and expecting them to continue to decrease, have decided
to drop the Small Craft Advisory.

A ridge of builds over the region Saturday into Sunday leading to
a return of northerly winds across the waters but the probability
for gusts exceeding 21-22 knots is very low, only around 5-10%
during this period. We continue to watch another potential trough
of low pressure in the Monday night through Tuesday timeframe
although confidence in the exact timing and impacts are only
moderate but most of the energy with this disturbance appears to
holds to our north at this time. -Batz/Schuldt

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Frost Advisory from 2 AM to 9 AM PDT Saturday for ORZ121.
WA...None.
PZ...None.
&&

$$

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