Debris Flow in Oregon, April 21 to 22, 2023

Area Forecast Discussion...Updated
National Weather Service Portland OR
952 PM PDT Fri Apr 21 2023

Updated Aviation and WWA Summary...

.SYNOPSIS...Spotty rain through tonight as a warm front lifts
northward across the region. Saturday looks mostly dry, mainly in the
afternoon...and milder. Could see 60s across interior for highs. Back
to rain on Sunday and Monday as another strong front moves across the
area. But, high pressure building next week, bringing a warming
trend, along with dry days.
&&

.SHORT TERM...(tonight through Monday)...

Take Away Messages:
  1) Milder for Saturday, with spotty rain early
  2) Wet for Sunday into Monday
  3) Dry, with warmer temperatures for later next week.

Plenty of clouds still streaming across the region this afternoon,
thanks to persistent westerly flow aloft. There is a weak warm front
offshore that will gradually lift northward tonight, and well to our
north Saturday morning. Been seeing occasional light rain to south of
a Astoria to Salem line this morning into early Fri afternoon. As the
front lifts slowly northward, will see this area of occasional rain
spread northward as well. As such, have boosted PoPs to Fri afternoon
through early Sat am. Overall, not large amounts of rain, as most
areas generally will get 0.05 to 0.20 inch (heaviest in usual spots
across the Coast Range/Willapa Hills). Snow level remains at/above
6000 ft, so no issues on the Cascades passes.

Should see milder air spread across northwest Oregon on Saturday.
With gradual breaking up of clouds, will see warm day for most areas.
MOS guidance suggesting only lower 60s, but feel this tad underdoing
the potential. So, will go with lower 60s for inland northern sites,
with 50s along the coast. But, where should see larger breaks in the
clouds, good bet will jump into the middle 60s. This area looks to be
mid/south Willamette Valley, including Salem to Corvallis to Eugene
areas. Will trend forecasts as such.

Not much change in the overall forecasts for Saturday night through
Monday. Another strong front will push into the region, with rain
increasing on Sunday. The deterministic model runs are in good
agreement showing another upper level trough moving into the area
Sunday. However, there are differences regarding the strength and
track. The ECMWF appears to have a deeper 500 mb low and tracks it
near KPDX by 12Z Monday. The GFS has a weaker trough with the main
energy more to the north. The NAM is even weaker than the GFS.
Orographic westerly 850 mb flow Sunday through Monday morning will
result in enhanced lift over the Coast Range, Willapa Hills and
Cascades for high POPS. Snow levels near 3500 feet Sun night, but
with couple inches expected on Cascades passes. 	/WeisKey

.LONG TERM...TUESDAY THROUGH FRIDAY...The main story for the long
term is the increasing likelihood of a change to warmer and drier
conditions beginning Tuesday. The deterministic GFS and ECMWF show an
amplifying 500 mb ridge building over the eastern Pacific Monday
night and Tuesday. However, some shower activity will continue Sunday
night through much of Monday with cyclonic upper level flow
continuing. A vast majority of EPS members for KPDX, KSLE and KEUG
indicate light QPF Monday. The WPC 500 mb clusters valid 00Z Tuesday
are in good agreement showing below normal 500 mb heights over the
Pacific Northwest. There is one cluster, heavily weighted toward the
Canadian model, that tries to bring the eastern Pacific ridge closer
to the coast.

The deterministic models and respective ensembles, as well as the WPC
500 mb clusters, are in great agreement showing well-above normal 500
mb heights pushing into the Pacific Northwest Tuesday. There is the
potential for some frost Tuesday morning as surface high pressure
strengthens. The favored areas would be the Hood River Valley and
southern Willamette Valley. The NBM shows max temperatures in the mid
60s Tuesday for the interior lowlands. However, the NBM Probabilistic
Generator gives a 51% chance of 70 degrees or more at PDX, 46% chance
for Kelso and Hillsboro, but only 21% chance at Eugene. As of April
20, PDX has gone 182 days since the last 70-degree day. Will Tuesday
be the day? If not Tuesday, then Wednesday could be the day as there
is around an 80% chance for 70 degrees or more at PDX and 75% or
greater chance for Hillsboro, Hood River and Kelso. The WPC 500 mb
clusters valid 00Z Thursday show well-above normal 500 mb heights
over the region, with some differences as to the upper ridge axis.
Cluster 1, made up of 75% Canadian, 40% GFS and 44% ECMWF show the
ridge axis directly over western Washington and Oregon. This cluster
closely resembles the grand cluster or total ensemble. A couple other
clusters keep the ridge axis offshore. There is at least moderate
forecast confidence that the warmer and drier pattern will continue
Friday. The warmer and drier pattern is also supported by the latest
6-10 day CPC outlook which give our area a 50-60 percent chance for
above normal temperatures and below normal precipitation. Weishaar

&&

.AVIATION...Moist, northwest flow aloft tonight under weak upper
level ridging. Occasional showers possible as a warm front lifts
northward. Expect a gradual trend toward MVFR at the inland
terminals as the front moves northward through 12z, with guidance
suggesting a 60-80% chance for cigs below FL030 after 10Z
Sat. Flight conditions will trend closer to IFR at the coast
tonight owing to low clouds and drizzle. Expect gradual
improvement from south to north on Saturday with most locations
becoming predominately VFR by 20z, though coastal terminals may
hold onto IFR or MVFR conditions a bit longer.

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

KPDX AND APPROACHES...VFR conditions expected to trend towards
MVFR by 10z Sat as cigs lower to FL025 with approaching warm
front. Flight conditions improve back to VFR by 20z Sat. Generally
light and variable winds expected. CB/DH

&&

.MARINE...A warm front is lifting north across the waters with
southerly winds to around 10 kt overnight. Then, a weak cold front
will approach the waters on Saturday while southerly winds
increase to around 10-15 kt, becoming westerly Sat night into
Sunday morning. Another weak frontal system moves across the
waters Sunday into Monday with gusts up to 20 kt.

The weather pattern appears likely to change towards the middle of
next week as high pressure builds into the region. There is a 70
to 80% chance that Small Craft Advisory northerly winds build
northward into the waters Tuesday into Wednesday.

Seas continue to hover around 10 to 12 ft with a period of 11
seconds early Friday afternoon, predominately from a persistent
northwest swell. Have extended the Small Craft Advisory for seas
through late this afternoon. Seas are expected to subside to
around 4 to 6 feet by Saturday morning. Also with the recent new
moon will have stronger tidal currents during the morning ebb
cycle. Those moving in and out of harbors and crossing coastal
bars should use caution and be aware of any bar restrictions in
place. /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

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