918 
FXUS66 KPQR 300411
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
910 PM PDT Thu Jun 29 2023

.SYNOPSIS...Onshore flow is expected to continue over the next 
week with mainly dry weather and above average temperatures. Patchy 
morning drizzle and fog along the north coast through Friday. Warm 
temperatures are expected through the weekend. However, a more 
substantial warming trend is likely early next week, which could 
cause impacts around the upcoming holiday.

&&

.SHORT TERM...Tonight through Saturday night...Shortwave ridging 
over the Pacific NW will slide eastward overnight while a shortwave 
trough over the Gulf of Alaska moves toward the British Columbia 
coast. At the surface, high pressure is expected to remain situated 
over the eastern Pacific with low pressure east of the Cascades. 
Onshore flow is expected to continue through the forecast period 
with strengthening surface pressure gradients which will lead to 
breezy west to northwest winds each afternoon and evening. Patchy 
drizzle and dense fog are also possible along the coast late tonight 
into Friday morning.  

Ensemble guidance remains in good agreement that the upper level 
trough will nudge farther south on Friday, lowering heights and 
producing mainly zonal flow over the PacNW through Saturday as the 
low moves through central British Columbia. Onshore flow will 
increase under this pattern with breezy northwest winds. Gusts up to 
20-25 mph are possible in the late afternoon and evening hours each 
day for inland locations and up to 30 mph along the coast.

Above normal temperatures continue into the weekend with lowland 
highs generally in the mid to upper 80s. Probabilities of 
temperatures reaching or exceeding 90 degrees Friday and Saturday 
range from 10-50% across the Willamette Valley, highest southward. 
Along the coast, temperatures will remain more mild due to the 
onshore flow influence with temperatures in the mid 60s to low 70s. 
DH/HEC

.LONG TERM...Sunday through Thursday...Hot and dry weather is the 
main theme for the extended forecast period. Overall, ensembles are 
trending into a more persistent weather pattern for early next week, 
though some uncertainty still remains, especially toward the middle 
of next week. WPC 500 mb clusters are showing high pressure ridging 
building over the NE Pacific and into the Gulf of Alaska Sunday and 
Monday while upper level troughing slides into central Canada. The 
GEFS and ECMWF ensembles extend weak shortwave troughing into the 
Pacific NW late Sunday into Monday. Then, heights build across the 
region on Tuesday. As that weak trough moves east, high pressure 
slowly builds east over the Washington/Oregon coast for Tuesday and 
Wednesday. More uncertainty remains for Wednesday as some clusters 
indicate troughing could develop again by Wednesday with others 
suggesting troughing will hold off until Thursday. At the surface, 
high pressure will remain situated over the eastern Pacific with a 
thermal trough pushing north over western Oregon Tuesday into 
Wednesday.

The result of this pattern is Sunday and Monday's temperatures 
remain fairly persistent from the mid 80s to lower 90s with 
temperatures rising rapidly Tuesday and Wednesday. NBM deterministic 
forecast is now indicating high temperatures for Tuesday (the 4th of 
July holiday) of 95-99 degrees and 93-97 degrees for Wednesday in 
the lowlands. ECMWF Extreme Forecast Index (EFI) is also indicating 
anomalously hot temperatures for Tuesday and Wednesday. NBM 
probabilities of temperatures reaching or exceeding 90 degrees 
continues to increase early next week for the lowlands, especially 
for Tuesday and Wednesday with 90-99% and 80-90% respectively. 
Additionally, probabilities of temperatures reaching or exceeding 
100 degrees have increased to 20-40% for Tuesday and Wednesday. 
These temperatures will create a moderate risk of heat related 
illness, especially for those planning on spending extended time 
outdoors around the holiday.  

Additionally, this pattern will likely create elevated fire 
weather concerns due to prolonged drying of fuels. Onshore flow 
is expected to continue through the forecast period with periods
of breezy northwesterly winds with gusts up to 20 mph in the 
afternoon and evening hours. These winds could exacerbate fire 
weather concerns, especially with holiday activities, though the
overall pattern does not suggest high fire weather concerns. Those
spending time outdoors should practice heat safety as well as 
fire safety. DH/HEC

&&

.AVIATION...As of 21z Thu, VFR prevailed district-wide except for
some patches of fog that are beginning to return to the coast as
NW flow increases. Model probabilities of IFR returning to the 
coast increase rapidly this evening, though the marine layer will
remain shallow and likely to clear by midday Fri. Inland areas 
should remain VFR, though latest hi-res guidance shows about a 
40-60% chance of IFR stratus developing at KPDX/KTTD between 
30/10z and 30/17z. Much will depend on whether or not a decaying 
front moving onshore into the Olympic Peninsula will hold together
long enough to deepen the marine layer near the mouth of the 
Columbia tonight, which would give marine stratus a better chance 
of reaching northern and eastern portions of the PDX metro Fri 
morning. Any morning clouds inland would clear out by midday, as 
latest hi-res guidance suggests a greater than 90% chance of VFR 
for the Willamette Valley by 18z Friday. N-NW winds will become 
gusty Friday afternoon, with gusts 20-25 kt possible along the 
coast and through the gaps in the Coast Range.

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

KPDX AND APPROACHES...VFR with mainly clear skies and typical
summertime afternoon onshore flow of 5-10 kt. High resolution 
guidance suggests a 40-50% chance of IFR between 10z and 17z Fri. 
By 18z Fri, there is a greater than 90% chance of VFR, which would
persist for the remainder of the day.  Weagle

&&

.MARINE...Here is a quick update for this evening. N-NW winds
have not ramped up to the degree as previously expected. Gusts
near the coast remain 15-20 kt from Cape Falcon southward,
therefore, Small Craft Advisory for our central/southern inner
waters (PZZ252/253) has been cancelled.

With high pressure in the northeast Pacific and low pressure in
California, we will continue to experience northwesterly winds. 
This pattern will bring gusts of 25-30 kt throughout Friday 
evening across the waters, lowering to 20-25kt gusts Saturday. 
With this expectation, beginning Friday evening, we have placed a 
Small Craft Advisory for our central and southern waters 
(PZZ252/272 and PZZ253/273) until early Saturday evening. 
Additionally, a Small Craft Advisory has been placed for our 
northern waters (PZZ251/271) from Friday evening to early Saturday
morning. JH

Previous marine discussion follows... 

The remains of an approaching Pacific frontal system appear to be
weakening too fast to allow much of a break in the N-NW winds
Friday. The more pertinent trend will be strengthening high
pressure over the NE Pacific as the remnants of the front fall 
apart Friday morning. The strengthening high pressure, combined 
with strengthening thermal low pressure near the OR/CA border, 
will result in strengthening N-NW winds expanding northward 
throughout the coastal waters Fri afternoon and evening. By 7 PM 
Friday, there is roughly an 80% chance that SCA-level winds will 
expand into our northern waters. Once this occurs, SCA-level winds
and steep seas will likely become a daily occurrence each 
afternoon and evening through at least early next week. There will
be some easing each night, mostly along the coast, but winds will
likely remain at SCA strength at night beyond 5 NM offshore. 

The one exception to the persistent, strong winds may again be 
across the northern waters (PZZ251/271) Fri night/Sat morning as 
an upper level trough moves onshore into British Columbia. But 
high pressure will strengthen rapidly behind this system, causing 
another quick increase in N winds and steepening seas, even for 
our northern waters, Saturday afternoon.

Dense fog remains possible in a shallow marine layer, and fog was
dense near the coast this morning. The above-mentioned decaying
front may deepen the marine layer sufficiently to avoid dense fog
north of Tillamook tonight, but fog appears to be more likely
south of roughly Cape Falcon. Latest hi-res guidance suggests
about a 70% chance of vsbys 1 NM or less across the inner waters
south of roughly Tillamook tonight, then these chances decrease
Friday morning. Will monitor trends in marine stratus/fog over 
the coming hours and we may issue a Dense Fog Advisory if 
conditions confirm model trends.  Weagle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 5 PM Friday to 3 AM PDT Saturday for 
     Coastal waters from Cape Shoalwater WA to Cape Falcon OR 
     out 60 NM.

     Small Craft Advisory from 11 AM Friday to 5 PM PDT Saturday for 
     Coastal waters from Cape Foulweather OR to Florence OR out 
     10 NM.Coastal waters from Cape Foulweather OR to Florence 
     OR from 10 to 60 NM.
&&


$$

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