NWS Portland, OR wrote its last area forecast discussion before the first event at Jul 24, 7:52 PM PST, 4 hours 8 minutes earlier.
Area forecast discussion, Jul 24, 7:52 PM PST, 4 hours 8 minutes before
Area Forecast Discussion
National Weather Service Portland OR
852 PM PDT Sun Jul 24 2022
Updated the first 36 hours of the Discussion, and Aviation
.SYNOPSIS...High pressure building into the Pacific Northwest will
bring an extended stretch of hot weather to inland valleys this
week, with the warmest highs expected mid-week. There may be
isolated thunderstorms Wednesday or Thursday as a shortwave rides
north along the western US coast.
&&
.DISCUSSION...Through Saturday.. Temperatures early this evening did
get warmer than forecasted, likely helped with just enough mixing
under clear skies to bring the quickly warming airmass aloft down to
the surface. Several spots in the Willamette Valley rose above 90
degrees late this afternoon into early evening. Marine stratus
continues to hug parts of the coast this evening, and is expected to
push back inland to the Coast Range within the next couple of hours.
The upper ridge west of Vancouver Island will be dropping southeast
overnight and into Monday to continue to warm the airmass aloft.
850mb temperatures are expected to increase into the 24-28C range
over Portland, yet forecast soundings continue to suggest that 850mb
temperatures will fail to mix out tomorrow, so not expecting readings
to reach 100 or higher, as depicted in the 75th percentile forecast.
Mid to upper 90s seem more likely, and though this would warrant an
Advisory under normal circumstances it marks the beginning of an
extended stretch of hot weather, so for simplicity sake we've elected
to begin an Excessive Heat Warning on Monday. Warning conditions are
more likely to be met on Tuesday, when PDX will have a 60% chance for
seeing triple digits. Taking all of the members in the extended grand
ensemble together, it would appear that either Tuesday or Wednesday
will be the hottest day in the period. Each day will have a 20-25%
chance for temperatures reaching/exceeding 105F in the Willamette
Valley, with temperatures likely (greater than a 75% chance,
according to NBM) to exceed 95F.One recent development in the
forecast however, is the HRRR Smoke has now modeled the appreciable
amounts of smoke coming from the Oak and Washburn fires in CA to
move north. The latest extended 48hr run spreads a decent amount
over Eugene by Monday night, then further north stretching from
Tillamook to Mt. Hood by Tuesday afternoon. Depending on the
opacity of the smoke, this could shave a few degrees off the
forecast and keep any chance of a triple digit reading off the
table. Will continue to monitor the fires activity, smoke produced,
and how the models are flowing it up in the atmosphere.
-Bumgardner/Kriederman
Beyond Wednesday, the dipole in ensemble guidance is still apparent,
with only 6% of the GEFS ensemble members vs 40% of the EPS's
members bringing 850 temps to above 26C by 00z Friday. Our forecast
continues to hedge towards the median of the NBM, which puts us
squarely in the middle of the GEFS-EPS tug of war and closest to the
mean of the CMC. Much of this is due to the difference between how
the GEFS and EPS systems are handling an upper low off the coast;
the GEFS brings it much closer to us, and hence flattens the ridge
and lowers heights over the PacNW, whereas the EPS builds the ridge
for one more day. In both ensembles, however, there is a downward
trend in 700hPa heights by Friday. Hence, despite a few extreme
outliers (as high as 109F) from the EPS, NBM's entire IQR shifts
downward a few degrees between Thursday and Friday, and then a few
more between Friday and Saturday, by which time it spans 87F to 95F
at PDX. It's important for us to stress that this does not imply an
absence of uncertainty - in fact, by definition, the maximum
temperature should fall outside of that range 50% of the time - but
simply a trend towards less oppressive temperatures. Hence, our team
has decided to go with an Excessive Heat Warning for the warmest
parts of our area - the northern and central Willamette Valley,
along with Clark Co. Washington - through Thursday, beyond which
time both confidence and temperatures decline. An Advisory will do
for everywhere else, save the coast and elevations above 4kft.
One thing we've been monitoring carefully is the potential for mid-
week convection, the likelihood of which is incredibly tough to pin
down due to disagreement among members of the grand ensemble.
Several members in each ensemble are now depicting QPF across some
part of our CWA during the mid to late week timeframe, though there
is very little temporal alignment. The deterministic GFS and
Canadian ensembles bring the most clear shortwave feature - a
northward moving band of enhanced cyclonic vorticity passing across
NW Oregon during the Wednesday afternoon through Thursday morning
period. Ironically, the EPS, which does not highlight such a
distinct feature and whose ensemble fails to support sufficient
instability for convective activity, does forecast lightning strikes
in the Cascades Wednesday evening. The Canadian's instability
forecast is the most impressive, as the mean of its ensemble has 342
J/kg of CAPE in Eugene Wednesday afternoon, while the maximum in the
EPS ensemble suggests 189 J/kg (its mean is 8 J/kg). This feature
will bear watching, as the NAM suggests flow along and ahead of this
feature, which will potentially induce a tropospheric fold, will
turn south-southeasterly; this means that any thunderstorms which do
manage to develop in the Cascades would move across our CWA rather
than out of it. For now, we'll continue to monitor the threat and
will message updates to our thinking accordingly. More clarity
should come when we get close enough to the event temporally to
utilize the CAMs, which will theoretically help pin down the timing
and strength of any mesoscale mechanisms to generate convection.
There are numerous additional, but more nebulous, perturbations in
the flow depicted by various ensemble models through the remainder of
the extended. We'll continue to watch. -Bumgardner
&&
.AVIATION...00Z TAFs: Expect VFR SKC over the inland areas
through Monday evening. The coastline will see areas of IFR to LIFR
conditions this evening through Monday morning, especially in the
vicinity of Capes. Otherwise, VFR conditions will prevail for the
coastal areas 18Z Monday through 00Z Tuesday. Northerly winds will
once again pick up Monday afternoon, with gusts to 20 kt expected
Monday afternoon along the coast, less than 09 kt for inland
terminals.
For detailed Pac NW aviation weather information, go online to:
https://weather.gov/zse
KPDX AND APPROACHES...VFR under mainly SKC through Monday evening.
Kriederman
&&
.MARINE...Typical summer pattern to continue through early in the
week. Northerlies will persist across the waters as high pressure
offshore remains the dominant features through Monday night. The
thermally induced surface trough looks to reach peak magnitude
this evening and then gradually weakens overnight through Monday.
Model guidance suggests 20-25 kt boundary layer wind speeds over
the waters south of Cascade Head through at least 18Z Monday. A
couple models indicate 30 kt boundary layer speeds south of Heceta
Head through this evening. Wind speeds gradually start to diminish
Monday afternoon and fall below advisory thresholds by Monday
night. Will extend the current advisories for wind and/or choppy
seas through Monday morning for the inner zones and into the
afternoon for the outer zones. Overall general wind speeds fall
to 10 kt or lower late Monday night or Tuesday morning and remain
there through late in the week.
Seas will be primarily wind-driven with a fresh swell component.
Guidance shows wave heights generally in the 5 to 7 ft range at
least through Tuesday. There is a high probability that seas will
reach 7 to 9 ft over the south zones through Monday. Spectral
guidance continues to show a 1-2 ft south to southwest background
swell. Will designate this as the primary swell through Monday
morning and put nearly all of the wave energy into the wind wave
component. By late Monday, once the wind diminishes, the existing
fresh swell will evolve into the primary swell. Forecast wave
periods of 7 to 8 seconds will result in steep and choppy
conditions. Wave heights settle into a 4-5 ft range for the latter
half of the week. Weishaar
For information about upcoming marine zone changes, go
online to: https://www.weather.gov/pqr/marinezone
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory from noon Monday to 9 PM PDT Thursday for Cascade
Foothills in Lane County-Cascades in Lane County-Central
Coast Range of Western Oregon-Coast Range of Northwest
Oregon-Lower Columbia-Northern Oregon Cascade Foothills-
Northern Oregon Cascades-South Willamette Valley.
Excessive Heat Warning from noon Monday to 9 PM PDT Thursday for
Central Columbia River Gorge-Central Willamette Valley-
Greater Portland Metro Area-Upper Hood River Valley-Western
Columbia River Gorge.
WA...Heat Advisory from noon Monday to 9 PM PDT Thursday for I-5
Corridor in Cowlitz County-South Washington Cascade
Foothills-South Washington Cascades-Willapa Hills.
Excessive Heat Warning from noon Monday to 9 PM PDT Thursday for
Central Columbia River Gorge-Greater Vancouver Area-Western
Columbia River Gorge.
PZ...Small Craft Advisory until 10 AM PDT Monday for coastal waters
from Cape Shoalwater WA to Florence OR out 10 nm.
Small Craft Advisory until 2 PM PDT Monday for coastal waters
from Cape Shoalwater WA to Florence OR from 10 to 60 nm.
&&
www.weather.gov/portland
Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland