561
FXUS66 KPQR 162221
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
321 PM PDT Tue Jul 16 2024

.SYNOPSIS...Hot and dry conditions today with afternoon highs
peaking around 95 to 100 degrees for interior lowland valleys.
A low pressure system will move northward this evening, leading
to a slight chance for isolated to scattered thunderstorms
through early Wednesday morning. Lightning and critically dry
fuels may result in numerous fire starts east of the Coast Range.
Thunderstorm outflow winds may also result in erratic fire
spread. Above-average temperatures continue through the long
term forecast while onshore flow persists at the coast.

&&

.SHORT TERM...Now through Thursday night...Conditions will be
hot and dry through the rest of the day, with temperatures
expected to peak around 95 to 100 degrees for interior lowland
valleys. The Heat Advisory for portions of the Portland/Vancouver
Metro Area, Columbia River Gorge, and Hood River area remains in
effect through 5 AM Wednesday. Overnight lows between 65 to 70
degrees for these locations will provide minimal relief from
the heat, contributing to localized Major HeatRisk. This level
of heat affects anyone without effective cooling and/or adequate
hydration. Meanwhile, northerly winds in the southern and
central Willamette Valley will shift southerly this evening as
the next weather system moves in, quickly cooling things down
by tonight.

An upper level trough off the northern CA/southern OR coast is
making it`s way north toward northwest Oregon and southwest
Washington. This will lead to a 15-25% chance of elevated
thunderstorms late this evening through early Wednesday morning.
This trough will be negatively-tilted, which is a favorable
pattern for enhancing lift, while advecting mid-level moisture
and instability. HREF guidance shows steep 700-500 mb lapse
rates around 8 deg C/km and upper level vorticity, which is
conducive for convection. Expect little precipitation with this
system, as the surface is very dry. Any rain that falls from
these elevated thunderstorms could evaporate before reaching
the surface, which may result in gusty outflow winds. Lightning
is also possible tonight with thunderstorms, which could lead
to fire starts due to very dry vegetation. As a result, Red
Flag Warnings have been issued for locations east of the Coast
Range beginning this evening. See the fire weather section for
more details.

Temperatures tomorrow (Wednesday) and Thursday will still be
very warm, but not as hot as today. Expect highs in the upper
80s to low 90s across interior lowland valleys, with 60s along
the coast as we maintain onshore flow. Winds will be westerly
to southwesterly as the upper trough exits the region, and non-
impactful. Gusts will be less than 10 mph for the majority of
the area, except the central Columbia River Gorge/Hood River
area where westerly winds could gust up to 20 mph. By late
Wednesday afternoon to Thursday, our area will be completely
free from shower and thunderstorm chances as the upper trough
will be far to our northeast.      -Alviz

&&

.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 persists
starting through at least 18Z 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 18Z 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... An upper level disturbance will push northward over
all waters through early Wednesday morning. This will result in an
increasing the chance of thunderstorms over the waters starting
late this afternoon through early Wednesday morning. 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 and PZZ273 around 5-6 PM then
gradually progress northward across all coastal waters through
Wednesday morning.

Expect a wind shift tonight with S-SW wind behind the line of
showers/thunderstorms. This will cause confused seas for a bit,
but fortunately combined seas should only be 4-6 ft at the time.
S-SW winds may briefly gust up to 25 kt, but then slowly ease
as the disturbance passes. Southerly winds will persist through
Wednesday, 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.
                                                   /42/Weagle

&&

.FIRE WEATHER...The previous Fire Weather Watches for all fire
weather zones east of the Coast Range have been upgraded to Red
Flag Warnings in coordination with neighboring offices. Conditions
will be hot and dry this afternoon, with relative humidities
falling as low as 15-20%. In addition, an incoming low pressure
system will bring a 15-25% chance for elevated thunderstorms
this evening through Wednesday morning, leading to increased
fire weather concerns.

Lightning strikes and critically dry fuels east of the Coast
Range may result in numerous fire starts. Expect little rain
with this system, as the surface is very dry. Any rain that
falls from these elevated thunderstorms could evaporate before
reaching the surface, which may result in gusty outflow winds.
Outflow winds from thunderstorms may also result in erratic fire
spread. Model guidance suggests a 10% chance for wind gusts in
excess of 50 mph from the strongest storms this evening,
particularly over the Oregon Cascades and Willamette Valley. As
of 1500 Tuesday, lightning strikes have already been observed in
the Lane County Cascades. Expect this trend to continue through
tomorrow morning, with the threat for thunderstorms gradually
moving northward going into tomorrow. Therefore, we staggered
the timing of the Red Flag Warnings to best match the progression
of the thunderstorm potential.     -Alviz

&&

.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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