916
FXUS66 KPQR 161738 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1037 AM PDT Tue Jul 16 2024

Updated Aviation and Marine Discussion

.SYNOPSIS...Rather hot today with highs approaching triple digits
for inland portions of SW Washington and NW Oregon. Slight chance of
thunderstorms for the central Oregon Cascades this afternoon. Then,
upper level disturbance brings increasing chances for elevated
convection later this evening and tonight from the Cascades to the
coastal waters. Above average temperatures expected to continue
through the weekend while onshore flow persists at the coast.

&&

.SHORT TERM...Today through Thursday...Hot and dry today, followed
by a chance for elevated convection tonight. An upper level cutoff
low has developed off the northern California coast this morning and
is expected to lift northeastward today toward the Oregon coast.
More southerly flow aloft ahead of the incoming shortwave is still
expected to draw in very warm 850 mb temperatures peaking around 23-
25C late this afternoon into NW Oregon and SW Washington. Expect
this to translate to highs around 95-100 degrees across the interior
valleys, including the Columbia River Gorge and Hood River Valley.
As the upper level disturbance approaches the region this evening,
high pressure building along the southern Oregon coast will drive a
strong onshore push of marine air at the surface. Expect a southerly
wind reversal to begin to cool temperatures in the southern
Willamette Valley by late afternoon/early evening, gradually
expanding northward overnight. With the warmer air lingering across
the Portland/Vancouver Metro to Hood River, will maintain the Heat
Advisory.

Along with the heat, the approaching shortwave will bring potential
for thunderstorms, initially surface based in the central Oregon
Cascades, eventually evolving into elevated nocturnal convection
later this evening and overnight. The upper level shortwave will
take on a negative tilt which is a favorable pattern for enhancing
lift, while mid level moisture and instability are advected
northward. Any thunderstorms that do develop will have the potential
to produce prolific lightning, presenting a threat for heightened
fire weather concerns given the recent stretch of hot and dry
weather. Currently have capped thunderstorm chances at around 20%,
though trends are certainly indicating the actual probability may be
higher than that, as models sometimes struggle with elevated
convection.

Temperatures are once again expected to warm to around 85-90 degrees
for Wednesday and Thursday across inland valleys as the ridge builds
back in. Onshore flow will maintain mild temperatures for the coast.
Upper level troughing will likely deepen the marine layer late
Thursday. /DH

.LONG TERM...Friday through Monday...Cluster analysis indicates the
ensemble guidance showing good agreement of the upper level ridge
amplifying and shifting back west for Friday and Saturday. This will
likely cause temperatures to bump back up a few degrees with highs
in the 90-95 degree range. NBM guidance suggests a slight cooling
trend into early next week as upper level troughing begins to nudge
into the Pacific NW. Something to watch will be the potential for
another cut-off low and shortwave trough to slide across the area
again this weekend, which could produce another round of
thunderstorms, but confidence remains low at this time. /DH

&&

.AVIATION...A complicated forecast for the airspace starting at
18Z Tuesday and going through at least 00Z Thursday. A low
pressure system swinging northward from California will result in
increasing instability and moisture aloft. This is resulting in a
20%-30% probability for SHRA/TSRA developing in SW Oregon and
moving northward through 00Z Thursday. Given that the convection
is aloft, flight conditions will likely remain VFR with the
potential for gusty and erratic winds near any thunderstorms.
Timing will be a challenge, but current guidance has PROB30 TSRA
starting for areas around KEUG starting around 00Z Wednesday,
pushing northward to KSLE around 06Z Wednesday and reaching KPDX
around 09Z Wednesday. Note that the TSRA potential will extend
from the Coast to the Cascades.

If a line of showers forms, it will likely come with a sharp wind
shift from NE winds ahead of it to S-SW winds behind it, which
will persist but ease for the remainder of the night.

To further complicate things, the aforementioned low will also
deepen the marine layer and result in a robust SW surge of marine
air pushing into inland areas. Expect IFR/MVFR conditions along
with -DZ (55%-65% probability), which will spread northward along
the coast behind the disturbance. MVFR stratus appears likely
(45%-55% probability) to reach KEUG around 09Z Wednesday, with
around a 20% probability of the MVFR conditions pushing into KSLE
by 15Z Wednesday.

PDX AND APPROACHES...Predominately VFR flight conditions.
Increasing chance of high-based PROB30 TSRA starting around
09Z Wednesday. Elevated nature of the SHRA/TSRA should keep VFR
flight conditions, but winds near any SHRA/TSRA will be gusty and
erratic. /42

&&

.MARINE...Upper level disturbance over the N CA waters
will lift northward today and tonight, increasing the chance of
thunderstorms over the waters overnight. This is the type of
system that has the ability to produce prolific lightning and
gusty/erratic outflow winds, so these thunderstorms could be more
hazardous than the weaker springtime storms that are more typical
for the coastal waters. Mariners planning on being out on the
waters tonight should pay close attention to the skies to the
south, and listen to NOAA weather radio for any Special Marine
Warnings. These showers/thunderstorms appear most likely to move
into our southern waters PZZ253/273 around 5-6 PM then gradually
progress northward through the coastal waters (and NW Oregon)
overnight.

N-NE winds today will shift suddenly to a gusty S-SW wind near the
line of showers/thunderstorms. This will cause confused seas for a
bit this evening, but fortunately combined seas should only be 5-6
ft at the time. S-SW winds may briefly gust 20-25 kt, but then
slowly ease overnight as the disturbance passes. South winds will
persist into Wed, but should only be 10-15 kt, easing from there
as high pressure returns Wed night and Thu. Thermal low pressure
re-strengthens over SW Oregon Friday, likely bringing a return of
gusty N winds to the Oregon and southern WA coastal waters.  Weagle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Heat Advisory until 8 AM PDT Wednesday for ORZ111-112-120-122.

WA...Heat Advisory until 8 AM PDT Wednesday for WAZ206-207-209-210.

PZ...None.

&&

$$

www.weather.gov/portland

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