Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 161636 AAA

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
934 AM PDT Mon May 16 2022

Updated Short Term, Aviation and Marine sections

.SYNOPSIS...A weak upper level trough will move across the region
today. Conditions improve Tuesday as weak high pressure develops. A
return to a cooler and wetter pattern is expected mid-week, with
snow levels lowering to just below the Cascade passes Wednesday
night. A return to dry and mild conditions occurs late next week and
into the weekend.

.SHORT TERM...(Today through Wednesday)...UPDATE:  At 16Z GOES-17
water vapor imagery showed the main frontal boundary east of the
Cascades. Visible imagery showed considerable lower level cloud cover
over the forecast area. Finally, KRTX doppler radar indicated
isolated shower activity over the Cascades. Current forecast is in
good shape. Main change was to remove POPS from the 00Z-03Z Tuesday
time period. The NAM and other high-resolution models show
strengthening surface high pressure late this afternoon through the
evening. A little cooler today as 850 mb temps fall about 3-4C
compared to yesterday. Weishaar

REMAINDER OF SHORT TERM: Showers ending this evening, with skies
clearing. Overall, rather tranquil pattern for tonight through
Tuesday evening, as weak transitory ridge shifts across the region.
Not much change on Tuesday as far as temperatures. But, will be dry.
With lot more in way of sunshine, will feel like a great mid-spring

.LONG TERM...(Wednesday through Sunday)...The next weather system
reaches the coast early Wednesday morning and then moves inland
during the day. Expected QPF amounts with this system look to be on
the order of one-quarter to one-half inch for the south Washington
and north Oregon coast and higher terrain and the south Washington
and north Oregon Cascades and foothills. Generally around a tenth of
an inch expected for the interior valleys.

Cascade snow levels lower to near 3500 feet Wednesday night. Not
expecting much in the way of snowfall accumulation as the bulk of the
QPF will have already occurred. The NBM shows 24-hr snowfall amounts
through 18Z Thursday up to 3 inches for the higher peaks. The
deterministic ECMWF has the main upper trough energy over the
northern Rockies 12Z Thursday. The 12Z operational GFS holds energy a
little more south and west. The WPC 500 mb clusters show slightly
differing solutions for the trough location. The model-mean cluster
has the largest 500 mb height anomalies focused along the Montana and
Canada border, closer to the 12Z ECMWF solution.

Models and their respective ensembles suggest an improving trend will
be in the works beginning Friday. There are couple of WPC clusters
that are slower to eject the upper trough eastward. However, 80
percent of the CMC ensembles are quicker with building 500 mb heights
just off the coast. Model differences become more apparent Saturday
as the deterministic ECMWF maintains ridging over the forecast area.
The GFS shows a much flatter ridge and brings the next frontal system
to the coast by 00Z Sunday. The WPC clusters favor some degree of
ridging, with the model ensemble mean indicating high pressure
centered along 130-135W. There are a few EPS members showing some QPF
for north Willamette Valley locations Saturday. Forecast confidence
lowers even more for Sunday. One WPC cluster has strong ridging
centered along the coast. Another cluster has the ridging suppressed
well to the south and a third cluster shows a large upper level
trough over much of the western U.S. Generally followed the NBM for
the weekend, using the NBM Experimental POPS.     /Weishaar


.AVIATION...18Z TAFS: Daytime heating under onshore flow should
allow the mixture of MVFR and low end VFR ceilings across the area
to lift solidly into VFR thresholds between 18-22z Monday. Inland
locations should remain predominantly VFR through 18z Tuesday, but
HREF model guidance does suggest a 20-30% chance that IFR to MVFR
ceilings could briefly develop around 12-15z Tuesday, particularly
around KPDX, KTTD and KSLE. Finally, the coast appears more
likely to be in the mix for MVFR conditions returning between
06-18z Tuesday, particularly around KAST, but even these values in
the HREF are generally only between 40-60% at any given hour.

For detailed regional Pac NW aviation weather information, go
online to:

KPDX AND APPROACHES...Daytime heating under onshore flow should
allow the mixture of MVFR and low end VFR ceilings across the area
to lift solidly into VFR thresholds between 18-20z Monday. Expect
these VFR conditions to persist through 18z Tuesday. With that
said, HREF model guidance does suggest a 20-30% chance that IFR
to MVFR ceilings could briefly develop around 12-15z Tuesday.


.MARINE...Weak high pressure will slowly build over the waters
today into Tuesday. Seas should more or less hold steady during
this time. The next front will push into the waters Tuesday night
and likely bring another round of high end Small Craft Advisory to
low end Gale Force wind gusts of 30 to 35 kt to the waters late
Tuesday night into early Wednesday morning. Seas should respond
accordingly and build to around 10 ft and become particularly
steep and hazardous. A coastal jet may result in winds being
strongest within 20 NM of the coast. Also, the strongest winds
appear more likely to exist off the south Washington and north
Oregon coast vs. the central coast of Oregon.

Models are coming into agreement high pressure should return to
the northeast Pacific late in the work week. This should bring a
quieter stretch of weather and allow seas to subside back below 5
ft towards next weekend.

Finally, we are in a very strong morning ebb cycle for those
traveling in and out of the bars up and down the Oregon and
Washington coast. /Neuman


PZ...Small Craft Advisory from 4 AM to 8 AM PDT Tuesday for Columbia
     River Bar.



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