Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 261115
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
406 AM PDT Tue Oct 26 2021

.SYNOPSIS...Active weather pattern continues as a parade of fronts
setting up of the north Pacific to bring rain to the region. First
system today then a lull for part of Wednesday. Then a fairly moist
system later Wednesday into late Thursday. High pressure should
build over the region Friday for a break in the rain through the
weekend.

&&

.SHORT TERM...Today through Thursday...Satellite reveals a jet stream
stretching across much of the north Pacific Ocean with the exit
region draping across CA. Upper and surface low in the Gulf of Alaska
near 51N 141W, heading east toward B.C.  An associated warm front now
spreading rain into the area will lift to the northeast this
afternoon with pcpn tapering off, but not ending, in the afternoon.
Will see breezy conditions again at the coast as well as inland as
the front moves through. The strongest winds inland likely in the
late morning and afternoon as the front lifts north and the pressure
gradient opens up with gusts in the 20-30 mph range. Snow levels
remain above pass levels but could see several inches above 6K ft .
today and tonight. Pcpn tapers off tonight, but next system now near
45N 170W, also developing on the strong jetstream, will track
towards the Pacific NW to bring more substantial rain to the area
later Wed through Thu. Current focus of the pcpn is over western WA
so for us the Willapa Hills and south WA coast and north OR
coast/coast range will get the bulk of the rain. GEFS and EPS show
the IVT mean in the 500-600 kg/ms along the WA/OR border later Wed
through Thu while mean IVT values range from 650 to 750 kg/ms for
the WA Olympic mountains as the baroclinic zone lay over western WA
on Thu. This boundary to the north will sag back southward later Thu
and Thu night as shortwave trough pushes into B.C.

.LONG TERM...Thursday night through Monday...The upper level trough
will dip south Thursday night into Friday pushing the boundary south.
By the end of this event currently expecting QPF totals around 2
inches for the north OR coastal mtns and Willapa Hills with 0.5 to 1
in for the lowlands Wed night to Fri time frame.

But increased uncertainty for the transition period with current
deterministic models handling the situation slightly differently.
The differences arise from the development cutoff low off northern
CA and where it ends up. The current ECMWF brings the cutoff low
closer to us thus slowing the progress of the front out of our area.
00Z Tue cluster analysis appears to favor the GFS and GEM solutions
with the cutoff further offshore Fri, so if correct should be drying
sooner.
Uncertainly continues Sat however, again with the placement of the
cutoff. For Sunday and Monday cluster analysis seems to favor more
ridging than not over the PacNW.  If this pans out, cool continental
airmass will filter into eastern WA/OR and flow offshore. Tight
gradients across the Columbia River Gorge could develop to produce
breezy conditions across the metro Sunday. Snow levels will also
drop across the Cascades to around 4500 ft but it`ll stay dry during
this time. /mh

&&

.AVIATION...12z TAFs: Rain will continue to expand in coverage
from west to east this morning as the latest front crosses the
region. Conditions are initially jumping between VFR/MVFR at the
coast and prevailing VFR at the inland terminals, but the bulk
of the guidance suggest cigs will lower to MVFR at most sites
between 12-15z as rain increases. The front should clear the
region by around mid day, with rain tapering to showers and cigs
trending back towards VFR after about 21z. Gusty south winds
will also accompany the front, gusting as high as 35-40 kt at the
coast this morning and 25-30kt in the Willamette Valley. Winds
will start to ease in the afternoon and evening.

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

KPDX AND APPROACHES...Conditions will trend towards MVFR through
15z as steadier rain develops ahead of a front, with cigs
lowering to around 2500 ft. Conditions should improve back to VFR
after 21z as rain tapers to showers behind the front. S-SW winds
could gust as high as 25-30kt at times in the morning, easing
back to around 10 kt after 00z Wed. /CB

&&

.MARINE...Another front is poised to move through the coastal
waters today, bringing a period of low-end southerly gales
through late this morning. The strongest gusts will likely be
found in a relatively narrow band from near the shore out to
about 30 nm offshore. Winds will veer west-southwesterly in the
afternoon behind the front, initially in the 20-25 kt range
before gradually trending down to 10-15 kt tonight through the
first half of Wednesday as weak high pressure moves overhead.
Meanwhile, the large swell moving through the waters is on its
way down this morning, with buoys currently showing about 15 ft.
The swell will further decay to about 10-12 feet by this
afternoon and then hold in that range through Wednesday morning.
A fresh swell will arrive during the afternoon and push seas back
to around 15 ft, maintaining Small Craft Advisory conditions
through Wednesday even as winds trend downward. Another (much
weaker) low will pass offshore Wednesday night, resulting in
another period of stronger southwesterlies. A reversal to
northerly winds looks likely during the end of the week as high
pressure builds offshore over the NE Pacific. /CB

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 5 AM PDT early this morning for
     coastal waters from Cape Shoalwater WA to Florence OR out 60 nm.


     Gale Warning from 5 AM PDT until 11 AM PDT this morning
     for coastal waters from Cape Shoalwater WA to Florence OR
     out 60 nm.

     Small Craft Advisory until noon PDT Wednesday for Columbia
     River Bar.

&&

$$


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