274 
FXUS66 KPQR 191804 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1103 AM PDT Tue Oct 19 2021

Updated Aviation and Marine Sections

.SYNOPSIS...After a brief break in the wet weather today, expect a
very active weather pattern to bring valley rain and high mountain
snow every 12-24 hours through early next week. A brief burst in wind
will be possible late tonight and Wednesday morning with additional
stronger bouts of wind possible over the weekend and/or early next
week. 


&&


.SHORT TERM...Today through Friday...Water vapor satellite imagery
reveals a shortwave ridge over the Pacific Northwest being shunted 
eastward as a shortwave trough over the eastern Pacific slides 
towards the region. Models are in good agreement this shortwave 
trough will take on a negative tilt as it pushes into the Pacific 
Northwest tonight. This will spread a band of rain from southwest to 
northeast across the area this evening/overnight. The fast moving 
nature of this system will limit rainfall totals. However, strong 
mid level forcing and modest low level convergence along the front 
will likely bring a burst of more intense rain, and perhaps more 
notably, some gusty winds. Several high resolution models suggest 
wind gusts between 30-45 mph will surface along portions of the 
coast and in at least isolated spots in the Willamette Valley around 
daybreak as winds aloft mix down with frontal passage and/or with 
convective elements embedded along the front. 

It should be noted that the operational GFS is an outlier within the
GEFS system, but does bear some resemblance to many members within
the EPS system and a few members in the CMCE system, all of which 
suggest a surface low pressure between 995-1003mb forming along the 
front off the Oregon coast as it shifts northeastward towards the 
region. This doesn't seem unreasonable given the pattern, but 
uncertainty in the magnitude of this embedded wave along the front 
does bring some uncertainty in whether or not stronger winds will be 
possible, particularly for the coast. The operational GFS's worst 
case scenario depiction would likely only result in marginal to low 
end High Wind Warning gusts of ~60 mph along the most exposed 
beaches and headlands from approximately Tillamook northward late 
tonight into early Wednesday morning. Many of the slightly weaker 
low pressure scenarios depicted by the EPS and CMCE members would 
likely produce sub-warning wind gusts. As a result, opted to 
increase winds along the coast to account for these windier 
solutions, but given most ensemble guidance suggests just a breezy 
period, will hold off on any wind highlights at this point. 

Meanwhile, models are in good agreement a shortwave trough racing 
eastward across the Aleutian Islands early this morning will 
interact with tropical moisture and result in one of the more 
impressive bomb-cyclogenesis events to occur in recent history off 
the Pacific Northwest coast Wednesday. Fortunately, the rapidly 
deepening low pressure will be far enough removed from OR/WA that 
the worst of the wind hazards accompanying it will remain well 
offshore Wednesday night into Thursday. In fact, ensemble guidance 
continues to support the idea that between the attendant front 
weakening as it approaches the region and pressure gradient forces 
remaining oriented strongly offshore, winds should remain well below 
High Wind criteria along our coastline. Nonetheless, this storm 
system will likely bring a solid shot of rain to the region late 
Thursday and it will generate a swell that will result in a sneaker 
wave threat along our coast Friday. Expect cooler temperatures 
Friday with precipitation turning more showery in nature. /Neuman


.LONG TERM...Friday night through Monday...There continues to be
above average agreement in the general weather pattern, which will 
feature a strong zonally oriented jet racing eastward across the 
Pacific Ocean towards northern California and southern Oregon. This 
will result in an extended stretch of particularly active weather 
across the Pacific Northwest that will feature below average 
temperatures with periods of rain/showers every 12-24 hours. NBM 
PoPs support this idea and generally range in the 80-95% range in 
each 12 hour period throughout the extended forecast. The first 
storm system of the extended forecast period will likely affect the 
region Friday night. A front should spread east-southeastward across 
the region Friday night and result in a solid shot of rain areawide 
with some potential for wind headlines along the coast depending on 
how the parent low pressure strengthens. Confidence in details 
beyond this time dwindles rapidly, though.

An operational model or two over the past day and a few more of the
00z ensemble members than 24 hours ago suggest a cyclogenesis event
occurring in the vicinity of our coastal waters over the weekend or
early next week. A few of these scenarios would almost certainly
result in high winds along our coast and in the Willamette Valley.
Nonetheless, it still appears to be a rather small percentage (~10%)
of the available ensemble guidance, but bears watching given the
pattern. /Neuman 


&&


.AVIATION...18Z TAFs: Generally VFR with high clouds over the
region late this morning. However, as of 1730Z there were still
some pockets of LIFR or lower conditions in the central and south
Willamette Valley. The 12Z HREF ensemble mean cloud cover
guidance and model soundings suggest increasing mid-level clouds
through the afternoon. The incoming frontal system is expected to
elongate and weaken as it approaches the coast this evening.
Expect rain to reach the coast between 04Z and 07Z, earliest
south of KONP. Rain gradually spreads inland after 07Z, but low-
level offshore flow through the Columbia Gorge will delay onset
of rainfall closer to 12Z Wed. The front reaches the coast south
of KONP around 12Z Wed, but not until 15Z or so along the south
Washington and north Oregon coast. Increasing MVFR conditions
will be likely for the coastal TAF sites overnight. Expect south
wind gusts 25-35kt along the coast associated with the frontal 
passage. Gusts 20-30kt likely inland between 12Z and 18Z Wed, 
especially south of a KTMK to KSLE line.

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

KPDX AND APPROACHES...VFR conditions are expected to continue
the evening, with cigs gradually lowering to 100 by 06Z Wed. Rain
develops between 07Z and 10Z, but cigs to remain VFR. East wind
gusts to 30 kt likely near KTTD and the west end of the Gorge
this afternoon through 12Z Wed. Weishaar

&&

.MARINE...A strong front will approach the outer waters this
afternoon. The latest models show this front elongating/weakening
as it moves through the outer waters. The 12Z model guidance
maintains the trend of depicting the strongest wind speeds over
the outer waters (beyond 20 nm). Will maintain the current gale
warnings. Some models show a strong wave on the front early Wed 
morning, but vary on the strength and timing of this feature. 
About 25 of 50 ECMWF ensemble members show gusts 40-48 kts at 12Z
Wed for buoy 46050. The favored time frame for gale force gusts
over the inner waters appears to be between 12Z and 18Z Wed. 

A second, potentially stronger, system is forecast to impact the
waters Wed night and Thu. Confidence is fairly high gale force
gusts will occur over PZZ270 and PZZ275. Less confidence in gale
force gusts over the inner zones. The parent low remains well
offshore with a majority of the individual ensemble members
showing the surface low tracking to the south British Columbia
coast Thu. The active pattern continues through the weekend with
additional gale force wind periods likely. 

Total wave heights will begin to ramp up over the outer waters
this afternoon and spread to the inner waters this evening. There
will be a substantial south wind wave component, up to 10-12 ft
over the far southwest portion of PZZ275, tonight. This will
result in combined seas into the upper teens for the outer
waters. Wave heights will be several feet lower over the inner
zones tonight, but still exceed 10 ft. Seas gradually subside
late tonight and Wed. The expected gales Thursday will allow seas
to rise into the 15 to 20 ft range with highest seas offshore. 
Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 AM PDT this morning for coastal   
    waters from Cape Shoalwater WA to Florence OR from 10 to 60 nm.

     Gale Warning until 11 AM PDT Wednesday for coastal waters from 
     Cape Shoalwater WA to Florence OR from 10 to 60 nm.

     Small Craft Advisory from 8 PM this evening to 2 AM PDT 
     Wednesday for coastal waters from Cape Shoalwater WA to 
     Florence OR out 10 nm.

     Gale Warning from 2 AM to 11 AM PDT Wednesday for coastal	     
    waters from Cape Shoalwater WA to Florence OR out 10 nm.

&&

$$