Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 012113

Area Forecast Discussion
National Weather Service Portland OR
213 PM PDT Thu Jun 1 2023

.SYNOPSIS...Slightly warmer today in most areas away from the
coast as onshore flow begins to weaken. Gradual warming trend
continues through the weekend and peaks with potential heat risk
concerns early next week, with highs in the low 90s likely by
Tuesday. Dry conditions expected to continue through the


.DISCUSSION...Very little change to the forecast package this
afernoon. Broad longwave troughing continues to encompass much
of the NE Pacific and Pacific Northwest this afternoon, anchored
by a deep upper level low south of the Gulf of Alaska. This
pattern maintains strong onshore flow and seasonably mild
temperatures across northwest Oregon and southwest Washington.
Expect temperatures to rebound by a few degrees into the lower
70s across the inland locations today as 850 mb temperatures
climb back to around 5-6 degrees C and weakening onshore flow
yields sunnier skies across the region this afternoon. A gradual
warming trend will continue into Friday as the pattern begins
to amplify and places the Pacific Northwest in southwest flow
aloft between the NE Pacific trough and an expansive ridge
covering much of the central and eastern CONUS. Latest model
guidance keeps highs in the upper 70s to around 80 degrees in
the Willamette Valley through the weekend as the upper low
shifts over northern British Columbia, allowing modest height
rises and 850 mb temps slowly increasing to 10-12 C over the
Pacific Northwest.

Latest medium range guidance continues to point to early next
week as the warmest days of this stretch, albeit with some
lingering uncertainty as to where high temperatures will
ultimately settle. In terms of the pattern, most model
solutions keep the ridge axis well to the east over the central
CONUS while one upper low drifts over the Northwest Territories
and another develops over southern California, keeping the
Pacific Northwest in a region of weak flow aloft between these
features. The most likely outcome for now would put highs on
Monday in the upper 80s and then climbing into the low 90s for
Tuesday, but NBM probabilities maintain a roughly 10-25 percent
chance highs to reach 100 degrees in the Willamette Valley on
Tuesday. Will continue to monitor Monday and Tuesday for
potential heat risk concerns, but it does appear that these
would be short lived as temperatures gradually moderate through
the middle of next week. Also, overnight temperatures are
forecast to remain cool in the 50s during this stretch.

Most of the area still looks to remain dry through the next
seven days, with shower chances returning along the Casacdes
early next week. /CB/HEC


.AVIATION...Dry, weak westerly flow aloft while onshore flow
persists in the lower levels. Satellite imagery as of 21Z Thu
afternoon shows mostly clear skies with scattered to broken clouds
north of KPDX around FL040-050. Expect predominately VFR across
the forecast area through this evening and into Friday morning.
Marine stratus will likely push back onshore around 10-12Z Friday
with MVFR cigs likely (~60-80% chance) at KAST, but only a 20-40%
chance at KONP. There is around a 20% chance that MVFR stratus
pushes across parts of the inland valleys after 12Z Friday
morning. Northwest winds continue with strongest gusts to 20 kt
along the coast.

For detailed Pac NW aviation weather information, go online to:

KPDX AND APPROACHES...VFR with mostly clear skies expected through
the period. Latest guidance suggests only a 10% chance of MVFR
stratus developing near the terminal Friday morning. Northwest
winds around 6-8 kt becoming light overnight. /DH


.MARINE...Surface high pressure remains offshore with low pressure
in northern CA into southwest OR. This will continue to bring
persistent north to northwest winds over the coastal waters
through the remainder of the week and into the weekend. Expect
peak winds today and Friday in the late afternoon through the
evening around 10-15 kt with gusts to 20 kt, with the strongest
winds across the southern zones and the inner waters nearshore.

General seas are expected to remain around 5 to 6 ft through
tonight supported by a persistent northwest swell at 10 to 11
seconds. Seas subside to around 4 to 5 ft on Friday as the
northwesterly swell subsides.

Northerlies are expected to increase this weekend as surface high
pressure strengthens offshore, tightening the pressure gradient
across the coastal waters. Latest model guidance suggests a 50-70%
chance of Gale Force gusts to around 35 kt on Sunday. High
pressure gradually weakens and northerlies ease somewhat into
early next week. /DH






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