906
FXUS66 KPQR 081030
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
330 AM PDT Wed May 8 2024

.SYNOPSIS...High pressure will build across the region into the
upcoming weekend, resulting in a prolonged period of dry weather with
rapidly warming temperatures. Near record breaking heat is in store
Friday and Saturday with widespread highs between 85-91 degrees
across inland valleys. Offshore flow transitions back onshore Sunday,
resulting in slightly cooler temperatures. There is no precipitation
in the forecast over the next week.

&&

.DISCUSSION...Wednesday through Tuesday night...After a chilly start
to the day with areas of early morning frost in outlying rural areas,
temps will quickly rebound Wednesday afternoon. Given plenty of
strong May sunshine and 850 mb temps around +6C, expect high temps
near 70 degrees over the Portland metro and mid to upper 60s over the
Cowlitz Valley and central/southern Willamette Valley. Despite plenty
of sun at the coast as well, light onshore flow during the afternoon
will prevent highs from warming much beyond 58-61 degrees according
to the latest iteration of the NBM. Suspect highs at the coast will
occur during the late morning/early afternoon before a sea breeze
develops and brings temps down a bit.

Temps will rapidly warm across the region Thursday into the weekend
as high pressure strengthens aloft and low-level offshore flow
develops. The latest suite of model ensemble guidance remains in
excellent agreement regarding exact temps, which is reflected well on
the NBM 1D Viewer`s box and whisker plots for forecast highs (the
model spread is extremely small with the NBM 10-90th percentile only
differing by three to four degrees or so). This means confidence is
high in regards to the temperature forecast.

So, how warm will it get? Given low-level offshore flow will be
ramping up Thursday with 850 mb temps warming to +10 to +12C by
Thursday afternoon, would expect widespread high temps in the low 80s
over inland valley.  The latest NBM probabilistic data still shows a
60-85% chance of reaching 80 degrees or warmer for the entire
Willamette Valley, with chances exceeding 90% for the lowlands of the
Portland metro area. Temps will warm even more Friday and Saturday as
strong ridging settles in, resulting in widespread highs in the mid
to upper 80s (except around 90 degrees over the Portland metro). Even
portions of the coast have a shot at reaching 80 degrees on Friday
(50-70% chance along the central coast, 10-30% north coast). Will
need offshore winds at the coast for most of the day for this to
occur, and it is not yet clear where the exact placement of the
thermal trough will be (slightly offshore versus hugging the
coastline versus slightly inland). Regardless of the outcome, the
coast will certainly be cooler Saturday when compared to Friday as
the thermal trough will almost certainly shift farther inland by
then. More widespread cooling is likely on Sunday as the thermal
trough focuses in on the Columbia Basin and pulls onshore flow all
the way to the Cascades. The marine layer will likely remain too
shallow for much in the way of morning cloudiness inland through
Sunday, but the upper ridge may weaken enough for some low clouds to
push into the inland valleys for a few hours Monday morning. Cannot
rule out patchy light drizzle at the coast Monday morning as well.

The unseasonably warm temperatures will no doubt cause some people to
flock to the rivers, lakes, and ocean beaches of SW Washington and NW
Oregon. It is important to remember that rivers and lakes remain
dangerously cold with water temperatures mainly in the 40s. Such
temperatures can easily cause cold water shock for those without
proper cold water gear. The bright sun and warm temperatures can make
the cold water look refreshing, but the consequences of jumping in
could be deadly. Be sure to bring a life vest and be extremely
cautious around area rivers, especially given the swift currents also
in place. Temps will likely cool back to seasonable normals early
next week, but conditions are still likely to trend dry as PoPs are
generally <15%. -TK/Weagle/HEC

&&

.AVIATION...VFR conditions continue, with generally clear skies.
Weak variable winds will gain a more defined northerly component
around 16-18z Wed. Inland terminals should remain under 8 kt, but
coastal terminals could see stronger gusts up to 20-25 kt at that
time. Slight to moderate chance (30-50%) of some low stratus
clouds at the northern coast and Cascade foothills from 12-18z,
bringing MVFR cigs. Terminals of most concern will be KAST and
KONP. Afterwards we return to VFR conditions.

PDX AND APPROACHES...VFR conditions continue with predominantly
clear skies. Slight chance (20%) of MVFR cigs due to low stratus
between
12-18z Wed, but these would be short lived if they do occur,
burning off quickly after sunrise Wed morning. Winds are currently
light and variable but will begin gusting from the north up to 8
kt around 18z. /JLiu

&&

.MARINE...High pressure is beginning to build across the waters,
bringing more tranquil weather. Winds turn northerly as high
pressure persists offshore and the thermal trough strengthens
along the CA/OR coast. This summer like pattern will bring breezy
north winds with gusts to 30 kt on Wednesday. Small Craft Advisory
remains on track for Wed afternoon through Wed night. Winds ease
somewhat Thursday morning, before pressure gradients strengthen
again through Thu evening. /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Frost Advisory until 8 AM PDT this morning for ORZ104-105-109-
     114>118-121-123>125.

WA...Frost Advisory until 8 AM PDT this morning for WAZ205-208.

PZ...Small Craft Advisory until 8 AM PDT this morning for PZZ210.

     Small Craft Advisory from 2 PM this afternoon to 2 AM PDT
     Thursday for PZZ251-271.

     Small Craft Advisory from 11 AM this morning to 5 AM PDT
     Thursday for PZZ252-253-272-273.

&&

$$

www.weather.gov/portland

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