513
FXUS66 KPQR 071019
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
319 AM PDT Fri Jun 7 2024

.SYNOPSIS...High pressure will maintain above-normal temps and
mostly dry conditions through early next week. Today will be the
warmest day of the week. A weak shortwave trough Saturday will
bring increasing mid to high level cloud cover and a 15-30%
chance for showers in the Cascades. The Lane County Cascades
have a slight chance for thunderstorms Saturday afternoon/night.
Onshore flow will keep temps moderated along the coast.

&&

.SHORT TERM...Today through Sunday...A high pressure ridge over
the Pacific Northwest will reach it`s maximum amplitude today,
leading to dry weather, sunshine, and the warmest temperatures
of the week. Afternoon highs today are forecast in the mid to
upper 80s for interior valleys, which are about 15 degrees above
normal for this time of year. NBM probabilities of exceeding 90
degrees has fallen to around 15-30% for the Portland Metro to
Upper Hood River Valley. Meanwhile, onshore flow will help keep
temps moderated along the coast, with highs in the upper 60s to
low 70s. Keep in mind that even though the air will be warm
tomorrow, rivers and lakes will still be very cold! Use extra
precaution if swimming in local bodies of water, as cold water
can lead to hypothermia or cold water shock.

Overnight, there will be decent relief from the warm temps as
Saturday morning lows are forecast in the 50s across the area.
The aforementioned ridge will also begin to progress eastward
as a weak upper-level shortwave trough approaches the region.
This shortwave will bring more moist, southwesterly flow aloft
as well as increasing mid to high level cloud cover Saturday.
Saturday high temps for inland valleys will still be warm and
around 10 degrees above normal, but likely a few degrees cooler
than the previous day due to increased cloud cover.

Precipitation with this shortwave trough is also unlikely since
our pre-existing air mass will dry. However, an exception would
be the Cascades, where surface heating and upslope flow could
support a 15-30% chance for showers Saturday afternoon-night.
HREF does show MUCAPE values of 250-500 J/kg Saturday afternoon
over the Cascades. And looking at SREF and HiResW-ARW soundings,
the instability is mainly above 10,000 ft. Combine that with
increased mid-level moisture, we could see an elevated
thunderstorm or two pop up along the Cascade crest. However,
with the westerly component to the wind aloft, any showers or
thunderstorms that do develop on Saturday would likely get
pushed into central and eastern Oregon. Went ahead and kept the
15-20% chance of thunderstorms given by NBM for the Lane County
Cascades.

The slight cooling trend continues on Sunday as the upper-level
shortwave trough moves over us and exits the Pacific Northwest.
We`ll have onshore flow which will help with cooling temps a
bit. However, temperatures are still forecast above-normal for
inland valleys, topping out in the upper 70s to low 80s. NBM
suggests a 40-50% chance that inland valleys exceed 80 degrees
on Sunday. Overall, pleasant summer-like conditions through the
weekend.      -Alviz

&&

.LONG TERM...Sunday Night through Thursday...To summarize, the
weather pattern in the early part of the extended forecast favors
a continuation of above-normal temperatures through Tuesday.
However, uncertainty comes mid-week with how an upper trough
near the Gulf of Alaska will influence the weather in the
Pacific Northwest:

Based on WPC cluster analyses, a low amplitude ridge will re-
build behind the shortwave trough Sunday night into Monday. The
clusters are also in agreement of above-normal 500 mb heights
through Tuesday. This will maintain warm temperatures going into
early next week. The latest NBM suggests a 40-50% chance of
inland valleys exceeding 80 degrees Monday and Tuesday. However,
all of the clusters show the ridge beginning to flatten on
Tuesday as an upper trough near the Gulf of Alaska progresses
into British Columbia. By Wednesday, ensembles are showing more
zonal flow, which would lead to further cooling of temperatures.

More uncertainty comes on Thursday with the upper level
pattern. About 50% of ensemble members show the upper trough
dipping southward toward the Pacific Northwest, increasing
southwesterly flow aloft. If this pans out, then we could see
even cooler temperatures and potential for precipitation.
Meanwhile, the other 50% of members show either zonal flow or a
building ridge. If these scenarios pan out, then we would
maintain relatively warmer and drier conditions.      -Alviz

&&

.AVIATION...High pressure persists through 12Z Saturday leading to
VFR CIGs and VIS. Onshore flow through the day with a northerly
wind in the afternoon. Misty conditions along the coast until
after sunrise around 15Z. Warm conditions are expected today,
especially from KPDX south to KEUG within the Willamette Valley,
and around K4S2. It is possible that thermals will be present
along runways. Winds will be northwesterly up to 3000 ft AGL up to
20 kt.

PDX AND APPROACHES...VFR with no concerns. Increased winds in the
afternoon. Thermal eddies possible in the afternoon along runways
due to elevated heating.  -Muessle

&&

.MARINE...High pressure remains through Saturday morning.
Northwesterly flow will dominate with gusty conditions up to 25
kt. Small craft advisory has been extended from Cape Falcon
southward through the evening as gusts will remain around 25 kt.
In the northern waters, those winds and seas will ease sooner.
Some models are suggesting a brief period of gusts to 25 kt in the
southern portions of PZZ271/251 from 1400-1900. Given that they
are going to be localized and isolated, have not continued the
advisory for the northern waters.

Seas will be around 7-9 ft at 13 seconds until Saturday when they
ease to less than 7 ft. This will be short-lived though because a
weak cold front arrives on Sunday causing winds to increase again
from the west. The westerly winds will combine with the westerly
background swell causing significant wave heights to rise near 10
ft. -Muessle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 8 AM PDT this morning for PZZ210.

     Small Craft Advisory until 6 AM PDT early this morning for
     PZZ251-271.

     Small Craft Advisory until 11 PM PDT this evening for PZZ252-253-
     272-273.
&&

$$

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