075
FXUS66 KPQR 280328 AAA
AFDPQR

Area Forecast Discussion...Updated
National Weather Service Portland OR
827 PM PDT Sat Apr 27 2024

.UPDATE...Only significant change this evening was to remove thunder
from Sunday`s forecast, as NBM thunder chances seem far too high
given deterministic models showing a strong cap near 9-10 kft. Even
if some updrafts over-achieve, the strong mid-level cap makes it hard
to imagine cells growing tall enough to achieve the requisite charge
separation for lightning. The coldest air aloft swings through
quickly early Monday morning, but 500 mb temps may remain cold enough
for deeper convection later in the day so will leave the thunder
mentions in the forecast for Monday.

Aviation discussion has also been updated below.  Weagle

&&

.SYNOPSIS...Front continues to bring rain this afternoon,
transitioning into showery conditions that will continue
through early next week. Wednesday and Thursday may have a
break from showers, but expect a return of precipitation into
next weekend.

.SHORT TERM...(Today through Tuesday)...Fast moving front
continues to move eastward, reaching the Cascades in the late
afternoon. Rain will transition to showers behind the front,
resulting in showers throughout the region by evening. Not much
rain expected from this front today, with 0.25 to 0.50 inch
(30-50% chance to exceed 0.5 inch) expected in the Coast Range
and Cascades, northward of Newport and Mt Jefferson (Oregon
Highway 20). Expect less rain across the coast and inland
valleys, around 0.10 to 0.25 inch. Otherwise, similar 24 hour
rainfall amounts for Monday and Tuesday, with Monday reaching
farther south in the Coast Range and Cascades unlike today and
Tuesday.

Cooler air aloft will push inland tonight as the front passes,
maintaining showers. This cooler air will steepen lapse rates
and bring some instability through Tuesday for southwest
Washington and northwest Oregon, as well as along the coast. As
a result, any cloud breaks during the afternoon could provide
enough warming to produce an isolated thunderstorm, most notably
Monday through Tuesday, with less chances Sunday. Will keep a
slight chance of isolated thunderstorms along the coast and for
inland areas north of a Lincoln City to Salem line through
Tuesday.

Sunday night, another fast moving system will move southeastward
into the region, bringing steady rain for a brief period before
transitioning to showers. As this system passes by and brings
cold air, snow levels of 4000-4500 feet will drop to 2000-2500
feet early Monday morning. As a result, 4-8 inches of 12 hour
snowfall across the Cascades is expected through Monday morning.
With chances around 50-60% of 12 hourly snowfall exceeding 6
inches Monday morning, as well as a late season drop of snow
levels, a Winter Weather Advisory has been issued from 11PM
Sunday to 11AM Monday for the Cascades.
-JH

.LONG TERM...(Wednesday through Friday)...Overall confidence is
low to moderate as the pattern stays rather progressive into
late next week. Deterministic and ensemble guidance continue to
struggle to resolve the longitudinal placement of ridge/trough
features going forward. Wednesday guidance has continued to
trend a little drier nudging a larger scale upper-level low
further north while a transient ridge glides over the region.
Out of all the ensemble solutions available, this scenario is
present in roughly 60% of them in addition to the latest
deterministic ECMWF and GFS. Thursday and beyond, model
uncertainty becomes truly significant with nearly a 50/50 split
between maintaining a ridge feature overhead or bringing a
potent trough into the region by Thursday and becoming most
defined Friday. Current confidence in the forecast by Thursday
is low.
-JH/Schuldt

&&

.AVIATION...A weak front will push across the area this evening
with continued scattered showers bringing lowered visibilities and
ceilings at times. Westerly flow aloft will persist through
Sunday with southwesterly winds at the surface. Predominately IFR
at the coast expected through at least 10-12Z, then gradual
improvement to MVFR possible Sunday morning. Mix of MVFR and VFR
inland tonight with CIGS bouncing between 2000-4000 ft through
08-10Z Sunday, then higher chances of becoming predominately VFR
after 12Z Sunday.

Notes: The ASOS at KTTD is only available via the dial in option.
The AWOS at KMMV is still out of commission. There is no
estimated time of repair.

PDX AND APPROACHES...MVFR with cigs around 2500-3000 ft through
08Z Sunday, becoming predominately VFR 3500-4500 ft through
Sunday evening. Light showers expected to persist through the
period. Southwest winds around 10 kt for much of the period. /DH

&&

.MARINE...Active weather is expected to continue this weekend into
next week. A surface front is moving through the waters this
afternoon and is expected to push inland by early evening. Winds
remain elevated and southerly along and ahead of the front with
gusts up to 30 kt, creating steep and choppy seas. A Small Craft
Advisory remains in effect until this evening. Winds will shift
westerly and decrease quickly behind the frontal passage this
afternoon and evening with gusts below 20 kt. The next surface
front will move through the waters late Sunday night into Monday
morning. Winds will increase again with local gusts up to 20 to 25
kts. Seas will generally be 6 to 9 ft at 11 to 13 seconds through
Monday.

Another frontal system is forecast to move through the waters late
Monday into Tuesday, producing elevated winds and seas in the low
teens. -HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Weather Advisory from 11 PM Sunday to 11 AM PDT Monday
     for ORZ126>128.

WA...Winter Weather Advisory from 11 PM Sunday to 11 AM PDT Monday
     for WAZ211.

PZ...None.

&&

$$

www.weather.gov/portland

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