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474
FXUS66 KPQR 180947
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
247 AM PDT Tue Jun 18 2024

.SYNOPSIS...
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Drier and sunnier weather returns today as
temperatures climb back near seasonal normals in the 70s inland.
Hotter conditions develop Wednesday through Saturday, peaking
Thursday into Friday as highs in the Portland area possibly
reach 90s degrees. Low pressure will moderate temperatures again
Sunday into early next week, with precipitation chances
remaining more uncertain.
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.DISCUSSION...
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Showers have mostly tapered off across northwest
Oregon and southwest Washington as of early Tuesday morning,
leaving a broken mid level cloud deck around 5000-6000 feet
lingering over the area. Expect these clouds to dissipate
through later this morning as northwest flow aloft and northerly
flow closer to the surface continue to advect drier air into
the region in the wake of the departing trough. Sunny skies this
afternoon, coupled with gradually rising 500 mb heights and 850
mb temps climbing to around 8-9 degrees C, will correspond to
high temps rebounding into the mid 70s across much of the area
this afternoon. Temps will remain more moderate at the coast as
a slight onshore component maintains the influence of the
marine layer.

Temperatures will continue their sharp upward trajectory on
Wednesday as the upper level pattern is characterized by a
developing Rex Block in the upper levels over the West Coast.
Closer to the surface, a strengthening thermal trough extending
from the California Central Valley into south-central Oregon
will induce cross barrier flow over the Casacdes and subsequent
downsloping for the interior lowlands. This will send highs
well into the 80s on Wednesday afternoon for areas away from the
coast, with NBM probabilistic guidance indicating a 30 percent
chance to reach 90 degrees across the Portland metro area.

The heat still looks to peak across the area Thursday into
Friday as high pressure continues to build over the region,
with model guidance deviating relatively little from previous
forecast packages. Operational NBM guidance as well as a
majority of GEFS, ECENS, and CMC individual ensemble members
continue to depict a most likely scenario of highs reaching
around 90 degrees from Portland to Salem and the mid to upper
80s towards Eugene both Thursday and Friday. However, NBM
probabilistic guidance continues to leave open the possibility
of a higher end solution, showing a 30-40 percent chance to
reach 95 degrees from the Portland metro area down to Salem on
Friday afternoon. This probability is notably much lower, closer
to 5 percent, into the south Willamette Valley as well as the
I-5 corridor in southwest Washington. Additionally overnight
lows are still forecast to drop into the upper 50s each night,
which will hopefully serve to somewhat mitigate more widespread
or cumulative HeatRisk concerns as the overnight period should
offer at least some relief each day. Still, will have to
continue to monitor the potential for highs to climb a bit
higher into the 90s toward the end of the week, particularly on
Friday.

Guidance shows good agreement on temperatures beginning to
trend downward on Friday as the Rex Block breaks down and high
pressure shifts east and opens the door to stronger onshore
flow. That said, still expect highs to reach into the mid 80s
for most interior locations on Saturday afternoon. More
substantial cooling should come on Sunday as WPC ensemble
clusters show good agreement on the next upper level trough
beginning to impact the Pacific Northwest, with temps back
closer to seasonal norms in the low to mid 70s. Precipitation
remains an iffier proposition as the core of the upper trough
remains north over BC, with NBM guidance holding onto 20-30 PoPs
along coastal areas and southwest Washington Sunday into Monday
while keeping the rest of the area dry through early next week.
/CB
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&&

.AVIATION...
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Upper level troughing moving across the region this
morning will shift east today with increasing northwesterly flow
aloft. Should maintain predominately VFR though increasing clouds
inland this morning with CIGS around 4000 to 6000 ft through the
morning. At the coast, best chance (~60%) for MVFR CIGS near KAST
through 18Z this morning. Farther south, light offshore flow
should maintain mostly clear skies. Low level flow turns bit more
northerly later this morning, increasing through the afternoon.
With dry northerly flow in the lower levels expect clouds to
gradually scatter becoming mostly clear later today.

PDX AND APPROACHES...VFR with broken CIGS around 4000 to 6000 ft.
There is a small chance (25-35%) of higher end MVFR CIGS between
10Z and 15Z. Clouds break up 18Z to 21Z, with VFR under mostly
clear skies afterwards. Expect northwest winds increasing up to 9
kt this afternoon/evening. /DH
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&&

.MARINE...
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Not much change as high pressure offshore is expected
to persist through the week. Northerly winds 5-10 kt across
coastal waters this morning increase to around 15-20 kt later
this afternoon as a thermal trough strengthens from northern CA
into southern OR. A Small Craft Advisory will be in effect south
of Cape Falcon through tonight. Expect will see periods of winds
gusting up to 25 kt through Friday during the late afternoon and
evenings. Latest guidance suggests a SCA will likely be needed
across all coastal waters for Wednesday and Thursday. Seas around
4 to 6 feet will generally be wind driven through the week. A weak
front is expected to approach the waters this weekend. /DH
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&&

.PQR WATCHES/WARNINGS/ADVISORIES...
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OR...None.
WA...None.
PZ...Small Craft Advisory from 5 PM this afternoon to 4 AM PDT
     Wednesday for PZZ252-272.
     Small Craft Advisory from 2 PM this afternoon to 4 AM PDT
     Wednesday for PZZ253-273.
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&&

$$

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