856
FXUS66 KPQR 191802 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1102 AM PDT Sat Oct 19 2024

Updated aviation and short term discussion.

.SYNOPSIS...Warmer and mostly dry today as light rain or
drizzle dissipates across the north this morning. A weak
atmospheric river will shift south across the area Sunday and
Sunday night, bringing widespread beneficial rain.

&&

.SHORT TERM...Now through Monday Night...Showers continue today
but accumulation will be minimal. The upper level pattern is
characterized by a flattened ridge extending from offshore of
northern California across southern Oregon. A lengthy feed of
moist, subtropical air riding the northern periphery of the
ridge is focused on the Pacific Northwest, producing a weak to
moderate atmospheric river aimed near the Strait of Juan de
Fuca. Ongoing light rain will taper off in most areas by later
this morning as the front dissipates, leaving warmer and mostly
dry conditions across most of our area today. Expect highs this
afternoon to jump back up into the low 70s in the interior
valleys as 850 mb temps warm to around 10 C. The atmospheric
river will remain well to the north through tonight, keeping any
rain focused mainly over far southwest Washington.

Widespread rain returns to the area beginning Sunday afternoon
as the atmospheric river is dislodged by an approaching trough
and shifts southeastward across western Oregon through early
Monday morning. Aside from the timing trending a bit later,
thinking has otherwise changed relatively little with regard to
rain amounts and expected impacts. IVT values still look to
peak in the 500-700 kg/m/s range across northwest Oregon Sunday
afternoon, with the atmospheric river continuing to weaken as it
shifts southeast across the area through Sunday night. Hi-res
guidance generally depicts rainfall rates peaking around a tenth
or two an hour, which coupled with the progressive nature of
the system would tend to limit any hydro impacts across the
area. Rainfall totals are also in line with previous thinking,
with probabilistic guidance depicting a ~95% chance for at
least a half inch of rain along the coast and a ~70% chance
farther inland through Sunday night.

Showery weather persists through Monday in the wake of the
atmospheric river as an elongated upper trough extends from
western Canada into the NE Pacific, with an embedded
disturbance moving across the area early Monday. -CB



.LONG TERM...Tuesday through Friday... Ensemble
clusters continue to show good agreement on broad upper level
ridge building over the western CONUS Tuesday into Wednesday as
a deep cutoff low develops well offshore. This will tend to
keep northwest Oregon and southwest Washington dry into the
middle of the week, with daytime temperatures near seasonal
norms in the low to mid 60s. Could see some renewed frost/freeze
concerns during the middle of the week as clear skies
contribute to efficient radiational cooling and chilly mornings.
Models indicate around an 80% probability that rain will return
to the region by Thursday as the ridge is displaced eastward by
the next trough approaching the West Coast.-CB


&&

.AVIATION...Expect primarily VFR conditions the rest of the
daytime and evening hours excluding the north Oregon Coast around
KAST where low MVFR cigs/vis likely persist through the forecast
period. Once we get into the overnight hours however guidance
favors a push of low stratus/fog up the Oregon coast with
deteriorating conditions for KONP by 09z. There`ll likely be
enough clearing, light winds, and surface moisture to support
fog/stratus formation in the Willamette Valley late overnight as
well with the highest confidence at KSLE, KUAO, and KHIO after
10-12z. Winds will remain southerly and under 10 kt for most of
the TAF period, with the exception of KAST/KONP gusting up to
20-25 knots at times.

PDX APPROACHES...VFR cigs/vis persist the remainder of the day
through the evening hours. There is a brief period Sunday morning
around 10-15z where there`s a 20-30% chance for MVFR to VFR
conditions but it`s more likely these degraded conditions hold to
the south - still worth mentioning. Winds hold under 10 knots
will shift a little more southerly this afternoon. -Schuldt

&&

.MARINE...
Low pressure across the central British Columbia coast
continues to move eastward, sending a warm front through the
Pacific Northwest. The surface pressure gradient has tightened
along the WA coast and along the OR coast north of Florence. This
continues to bring Small Craft Advisory gusts of 20 to 30 knots
from Cape Shoalwater WA to Florence OR. By 5AM Saturday, low-end
Gales across the inner water zone (PZZ251) will ramp down into
Small Craft criteria. As a result, have issued a Small Craft
Advisory to replace the Gale Warning from 5AM Saturday to 8PM
Sunday. Similarly, winds will also ramp down to below Small Craft
criteria between Florence and Cape Foulweather by the
aforementioned time, so will not extent this advisory.

A very strong ebb is expected this evening for the Columbia River
Bar. Current Gale winds are expected to lower to Small Craft
criteria by 5AM Saturday, therefore a Small Craft Advisory has
been issued from 5AM Saturday to 8PM Sunday.-Hall/Batz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 2 PM PDT Sunday for PZZ210-251-271.
     Small Craft Advisory until 8 PM PDT this evening for PZZ252-
     272.
     Small Craft Advisory from 8 AM to 2 PM PDT Sunday for PZZ252-
     253-272-273.
&&

$$

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