298
FXUS66 KPQR 071810
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1059 AM PDT Fri Jun 7 2024

.SYNOPSIS...High pressure of varying intensity across the Pacific
Northwest will maintain mostly above average temperatures through at
least the middle of next week. Precipitation chances remain low
during this period, but peak across the Cascades late Saturday into
early Sunday and then across coastal areas and southwest Washington
Monday night into Tuesday.

&&

.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...Surface high pressure offshore and lower surface pressure
over the Great Basin will lead to a typical summertime northwesterly
wind regime across northwest Oregon and southwest Washington with
predominantly VFR conditions areawide through
18z Saturday. The main exception to that statement will be along
the immediate coast where upwelling near the coast will bring a
20-40% chance of low end MVFR or IFR conditions developing between
approximately 07z and 18z Saturday.

PDX AND APPROACHES...Surface high pressure offshore and lower
surface pressure over the Great Basin will lead to a typical
summertime northwesterly wind regime with VFR conditions through
18z Saturday. /Neuman

&&

.MARINE...Surface high pressure remains anchored over the
northeast Pacific with thermally induced lower pressure residing
over the Great Basin. This will result in northerly wind gusts
increasing across the waters this afternoon with a >80% chance
that wind gusts exceed 21 kt for a period this afternoon and early
evening from Cape Falcon southward. The current Small Craft
Advisory covers this hazard well. Northerly winds today and
upwelling along the coast will bring a 20-40% chance of a low
cloud deck forming along the immediate coast overnight that could
bring locally dense fog to primarily the inner waters Saturday
morning, but at this point confidence is still relatively low this
will come to fruition.

Gusty winds will subside a bit earlier overnight than is typical
in these summertime northerly wind patterns as a weak front
pushes into the northeast Pacific and weakens the surface high
pressure. The main impact from this front will be for seas to
temporarily climb back into the 7-9 ft range Sunday.

Another weak front may brush the waters early next week, but the
probability for winds to rise into Small Craft Advisory thresholds
of 21 kt or more is less than 30%. There is good agreement
northerly winds will strengthen midweek with over an 80% chance
that Small Craft Advisory level wind gusts of 21 kt or more return.
Seas look to respond accordingly and appear most likely to climb
back into the 7-9 ft range during that time as well.

There will be another very strong ebb current early Saturday
morning so will be issuing another Small Craft Advisory for Rough
Bar conditions for a 4-5 hour time window centered around the
strongest ebb current. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for
PZZ252-253-272-273.
&&

$$

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