154
FXUS66 KPQR 031047
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
346 AM PDT Mon Jun 3 2024

.SYNOPSIS...Low pressure approaching Vancouver Island is pushing a
cold front across western WA/OR this morning. This is bringing an end
to the steady precipitation early this morning, leaving scattered
showers for the remainder of the day. Another disturbance is likely
to bring rain to much of SW Washington and portions of NW Oregon
tonight into Tuesday. Temperatures remain on the cool side of normal
through Tuesday, but a strengthening upper level ridge will lead to
warmer and drier weather later in the week.

&&

.SHORT TERM...Today through Wednesday...Steady rain is coming to an
end across SW Washington and NW Oregon early this morning as a cold
front moves onshore, pushing the deepest moisture and strongest
forcing east and south of the forecast area. This system slightly
underperformed expectations in terms of QPF, as rain arrived a few
hours later than expected Sunday and the rainfall rates weren`t quite
as high as they could`ve been given the moisture flux involved. That
said, this was still an impressive rain event by early June standards
with most inland valleys recording 0.50-1.00" of rain, and 1.50-3.00"
for much of the coast and higher terrain in our forecast area. A few
RAWS stations have seen more than 3 inches of rain from this event,
with the big winner thus far being Cedar RAWS with 3.63" as of 210
AM.

Latest imagery from KRTX/KLGX Doppler radars suggest the shower
activity upstream is paltry, which is not surprising considering the
lack of a significant cold pool aloft. 09z RAP analysis does show a
modest cold pool moving onshore near Cape Flattery, with 500 mb temps
as low as -24 deg C in its core. However, the 500 mb temps expected
to advect into our area are milder, which will effectively cap any
showers at 10-15 kft. Suspect there will be enough shallow
instability from the heating of the day to support scattered showers,
but it is highly unlikely (though not impossible) they will be able
to grow tall enough to generate lightning. Given the moisture in
place, even these shallow showers will be capable of producing brief
heavy downpours today - but these will be of the hit-and-miss
variety.

Looking farther west, GOES-West infrared imagery shows a baroclinic
leaf associated with our next developing system near 47N/145W. It is
notable that the GEFS maintains an atmospheric river of nearly the
same strength as Sunday`s as this next system moves into western WA
and northwest OR tonight into Tuesday, though the EC ensemble suite
is weaker. Regardless, the forcing will be considerably weaker than
Sunday afternoon and evening, so QPF will be considerably less than
with Sunday`s system. Given the deep moisture in place and despite
the weak forcing, the higher terrain of our northern zones stand to
see another decent shot of rain, with HREF means showing 0.75-1.50"
and HREF 90th percentile QPF showing 1-2" with some bullseyes in
excess of 2 inches. The inland valleys are much drier, with HREF
means showing 0.10-0.25" except for a band of 0.25-0.50" near
Kelso/Longview. The overarching point here is that tonight into
Tuesday will likely be wet for SW Washington and much of the Oregon
coast while the inland valleys are less wet with generally spotty
light rain.

High pressure begins to build into the Pac NW from the southwest
Tuesday night into Wednesday, which will be the beginning of the end
of our unseasonable cool and wet pattern. Temperatures Wednesday will
climb closer to seasonal norms, and should be mostly dry aside from
some morning clouds and spotty light showers.  Weagle


.LONG TERM...Thursday through Sunday...High pressure will strengthen
over the Pac NW Thursday, as a warmer air mass bulges northward from
California. This will continue the warming and drying trend, with
temperatures potentially reaching the 80s as early as Thursday. This
is supported by the NBM probabilistic guidance, which shows general
50-80% chances of our interior lowlands reaching 80 degrees. This
should begin a prolonged period of above normal temperatures for SW
Washington/NW Oregon.

One development over the past 24 hours is that models and their
ensembles have generally shifted the upper ridge axis east of the
Cascades, which should maintain some degree of onshore flow for the
Pac NW. This will likely keep the coast and coastal valleys cooler
than their inland counterparts through the upcoming weekend. Another
development is the potential for shortwave energy to come into play
Saturday, which will increase the potential for showers and
thunderstorms across the Cascades. All in all, it appears the hottest
model solutions from a couple days ago will not come to fruition, and
this is also reflected in the near complete removal of any chance of
reaching 100 degrees by NBM probabilistic guidance for Friday and
Saturday. The NBM probs of reaching 90 degrees are generally 25-55%
for the Willamette Valley Friday and Saturday, so our forecast
generally has highs in the mid 80s to lower 90s both days for the
inland valleys.

Given the recent rain and the lack of any strong offshore flow going
into this late week/weekend warm spell, there could be a touch of
humidity, and nights will likely remain mild - especially in the
urban centers.Weagle

&&

.AVIATION...MVFR prevailing inland with a mix of MVFR and IFR at
the coast. As a cold front moves through this morning expect an
improving trend starting around 12Z Mon. In the post-frontal
showers expect a mix of MVFR to VFR through the day. Next system
approaches overnight with IFR conditions returning to the coast after
09Z Tue. Inland remains predominantly VFR, but MVFR probabilities
start to increase to around 20-50% towards 12Z Tue.

Breezy southwesterly winds continue today, then gradually ease in
the late afternoon and evening hours. Winds increase tonight at
the coast as the next front approaches. Expect southerly gusts
30-40 kt at the coast after 06Z Tue.

PDX AND APPROACHES...Post-frontal environment with showers and
intermittent MVFR/VFR cigs, but HREF indicating MVFR chance
decrease through the day. Winds will be southwesterly 10-15 kt
with gusts to 20-25 kt through the afternoon, then easing in the
evening. /mh

&&

.MARINE...In the post-frontal environment will continue gusty
winds and steep seas today. Not much of a break as another front
moves to the waters. High probabilities for gales HREF with good
agreement with deterministic models give high forecast confidence
to issue a Gale Warning for the zones north of Cape Foulweather
including the Columbia River Bar for later tonight into early
Tuesday. Small Craft Advisories continue for the zones south of
Cape Foulweather through Tuesday afternoon.

High pressure builds midweek for more settled conditions for the
remainder of the week. Expect a summer type pattern with high
pressure offshore with a thermal trough along the coast. This may
bring northerly winds gusting to 25 kt at times to late in the
week.
/mh

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for
     PZZ210-251-252-271-272.

     Gale Warning from 11 PM this evening to 8 AM PDT Tuesday for
     PZZ210-251-252-271-272.

     Small Craft Advisory until 5 PM PDT Tuesday for PZZ253-273.
&&

$$

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