Small Craft Advisory 115, NWS Portland, OR

Area Forecast Discussion
National Weather Service Portland OR
1117 AM PDT Wed Aug 11 2021

Updated aviation and marine sections...

.SYNOPSIS...High pressure will continue across the region through
Friday leading to hot and dry weather. An excessive heat warning is
in effect from noon Wednesday to Saturday evening. The upper ridge
will shift east this weekend with a slight cooling trend starting
Saturday and continuing into early next week.

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.SHORT TERM...TODAY THROUGH FRIDAY...Water vapor satellite imagery
early Wednesday morning shows an upper level ridge extending across
the northeast Pacific, the Gulf of Alaska and into the Pacific
Northwest. The upper high currently centered southwest of Vancouver
Island will expand across much of the PNW today, while the upper
ridge gradually shifts eastward during the next few days. This
weather pattern will bring a continuation of dry weather and
increasing temperatures as the atmosphere continues to be compressed
and warmed near the surface.

Temperatures will rapidly increase during the day today into the
upper 90s to near 100F, at least 15 degrees above normal for mid
August. Model forecast soundings indicate 850 mb temperatures of
around 20C this morning will warm to around 25C by Thursday, which
if mixed to the surface, would yield a temperature of 104F. This is
certainly possible Thursday as the upper ridge axis will be
positioned along the coast extending northward into British
Columbia. Record high temperatures at PDX during this time of year
have been recorded in the 102-107F range. But there is still a
substantial amount of uncertainty that temperatures will reach this
high, as indicated by the NBM. Under clear skies much of the
Willamette Valley and southwest Washington will more likely than not
reach the 100 degree mark. The latest HRRR smoke model shows
increasing chances of high level haze over the area Thursday which
could limit the amount of surface warming. It is interesting to note
the NBM has a 10% chance for temperatures reaching 105F at PDX
(worst case scenario), while also showing a 10% chance of
temperatures only reaching 90F ("best" case scenario). Will continue
with most likely scenario of inland temperatures 15 to 20 degrees
above normal on Thursday.

Coastal locations may see a brief warm up, especially the northern
Oregon and south Washington coast, to near 80F. But the central
Oregon coast is expected to remain near normal under the influence
of the marine airmass.

Friday also has the possibility of being somewhat interesting as the
upper ridge begins to shift east. There are still subtle differences
between deterministic models but generally show a weak upper low
lifting north off the northern California coast. This would allow
increasing southerly flow aloft, and depending on the amount of
midlevel moisture available, could initiate some convection across
parts of southern and central OR, including the central OR Cascades
in Lane County. 850 mb temperatures should still be around 25C
Friday, so similar temperatures may be possible, but if cloud
coverage increases, temps would likely be slightly lower. Models
also indicate possible southwest marine push increasing along the
central coast Friday morning with some influence felt into the
southern Willamette Valley. Lowered daytime high temperatures back
into the mid to upper 90s here, while keeping temps from Salem
northward around 100-102F. Overnight temperatures may not provide
much relief, as temperatures generally remain above 70F. More rural
locations, though are more likely to fall into the mid 60s.

The Excessive Heat Warning will be in effect beginning noon today
covering the majority of the CWA, excluding the coast. With the
widespread heat expected, there is an enhanced risk to sensitive
groups. Drink lots of water, check on neighbors, friends and family
often, and locate to a cool space during the peak heating time
frames. Refer to local emergency management agencies to find cooling
sites near you.  /DDH

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.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY...By Saturday, the
ridge will shift further inland and more of a true onshore flow
pattern will take over. Temperatures will begin to slowly cool
starting Saturday afternoon, although still expecting 90F+ degree
temperatures inland. All coastal areas should return to a more
normal temperature pattern. By Sunday models show a low dropping
down over the southern Alaska Panhandle. Some indication of light
rain possible by ensembles and the NBM so have included a slight
chance POP for Sunday night. WPC 500 mb cluster analysis shows
general broad troughing over the Pacific Northwest Monday. This
indicates temperatures should continue to cool with more mild and
seasonable conditions expected by Monday.

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.AVIATION...High pressure over the region will result in
predominantly VFR conditions areawide through 18z Thursday. The
main exception to this will be along the coast where a southerly
wind reversal and fog and low clouds will spread northward up the
coast tonight. This will likely result in a mix of IFR and LIFR
conditions pushing into KONP between 06-12z Thursday. There is a
chance it could push all the way northward and impact KAST between
12-18z Thursday, but nearly all of the model guidance
available suggests it will fall short.

Smoke from the wildfires burning in the Oregon Cascades will
continue to primarily impact eastern Lane, Linn and Marion
Counties over the next 24 hours. The latest HRRR smoke model
does suggest some smoke from BC/WA wildfires will drop
southwestward through the Columbia River Basin and begin to
impact the Columbia River Gorge and northern Willamette Valley
shortly after 18z Thursday. Do not expect this to bring IFR
restrictions at this point, but would expect the skies to become
noticeably more hazy with surface visibilities perhaps dropping
into the 5-9 mile range. Confidence is not terribly high that
visibilities will drop even that low, though, considering the smoke
field does not appear all that impressive on satellite imagery in
the source region of eastern Washington and southern British
Columbia.

For detailed regional Pac NW aviation weather information, go
online to: https://weather.gov/zse

KPDX AND APPROACHES...High pressure aloft will result in light
winds and VFR conditions through 18z Thursday. Some smoke from
BC/WA wildfires will begin to spread westward through the
Columbia River Gorge shortly after 18z Thursday and may result in
surface visibilities falling into the 5-9 mile range. Confidence
is relatively low that visibilities will drop even into those
values considering the smoke field does not appear all that
impressive on satellite imagery in the source region. /Neuman

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.MARINE...High pressure over the northeast Pacific and a thermally
induced lower pressure over western Oregon will result in breezy
northerly winds today. There could be a few isolated spots with
gusts to 21 kt in the afternoon, but do not expect wind gusts this
strong to be widespread enough to necessitate a Small Craft
Advisory.

A southerly wind reversal will move northward up the coast
bringing areas of fog and a brief burst of 10 to 20 kt southerly
wind gusts tonight into Thursday. Southerly winds should then more
or less persist through the weekend, but remain well below Small
Craft Advisory thresholds of 21-25 kt. Expect seas to climb into the
7 to 9 ft range over the next 24 hours as an incoming northwesterly
swell pushes into the waters. Seas should gradually decrease
thereafter and drop below 5 ft for the weekend. /Neuman

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.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning until 10 PM PDT Saturday for Cascade
     Foothills in Lane County-Cascades in Lane County-Central
     Coast Range of Western Oregon-Central Columbia River Gorge-
     Central Willamette Valley-Coast Range of Northwest Oregon-
     Greater Portland Metro Area-Lower Columbia-Northern Oregon
     Cascade Foothills-Northern Oregon Cascades-South
     Willamette Valley-Upper Hood River Valley-Western Columbia
     River Gorge.

WA...Excessive Heat Warning until 10 PM PDT Saturday for Central
     Columbia River Gorge-Greater Vancouver Area-I-5 Corridor
     in Cowlitz County-South Washington Cascade Foothills-South
     Washington Cascades-Western Columbia River Gorge.

PZ...Small Craft Advisory until noon PDT today for Waters from
     Cascade Head to Florence OR from 10 to 60 NM.

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