696
FXUS66 KPQR 011752 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1052 AM PDT Wed May 1 2024

Updated aviation discussion and hazards.


&&

.SYNOPSIS...Mostly dry conditions prevail today before another
system arrives this evening into Thursday morning. This will
bring another round of rain and mountain snow above 4000 ft.
Heaviest snowfall will be above 5500 ft. A more robust system
arrives Friday, with forecast precipitation around 0.75-1.5 inch
across northwest Oregon and southwest Washington. Snow levels
Friday will rise above 6500 ft. Rivers still have a less than 5%
chance of reaching action stage. Wet, unsettled weather likely
continues over the weekend through at least early next week.

&&

.SHORT TERM...Now through Thursday night...Conditions will be
mostly dry today before the next system arrives this evening.
We`ll have some relatively warmer high temperatures today
compared to what we`ve experienced the last couple days.
Afternoon highs are forecast in the low 50s along the coast,
upper 50s/low 60s for inland valleys, and 40s for higher
terrain.

The next low pressure system will arrive Wednesday evening to
Thursday morning, bringing another round of precipitation.
Expect lowland rain showers and Cascade snow showers, with snow
levels around 4000-4500 ft. The bulk of the snow will be above
the Cascade passes. 24 hr snow amounts ending 5 PM Thursday are
forecast around 2-5 inches above 4000 ft, except up to 10
inches above 5500 ft. Have decided not to issue a Winter
Weather Advisory for the Cascades considering that the heaviest
snowfall for this system will be above the passes and forecast
snow amounts look less than what we`ve seen with the previous
systems earlier this week. Current NBM guidance suggests a less
than 5% chance that the Cascade passes see 24 hr snowfall greater
than 5 inches ending 5 PM Thursday.

Thursday afternoon to late Thursday night, conditions will dry
up briefly before another system approaches the Pacific
Northwest on Friday.     -Alviz


.LONG TERM...Friday through Tuesday...The long term forecast is
characterized by wet, unsettled weather as a series of systems
pushes through the Pacific Northwest. WPC cluster analyses are
in agreement of another trough pushing through the region on
Friday. This looks like a stronger system with abundant moisture
as GEFS and ECMWF ensemble members show IVT values peaking
between 250-500 kg/ms on Friday.

The latest NBM guidance suggests a 25-45% chance that 24 hr QPF
ending 11 AM Saturday exceeds 2 inches for the Coast Range and
Cascades. For inland valleys, this probability is less than 5%.
For now, our current 24 hr QPF forecast ending 11 AM Saturday
calls for 0.75-1 inch for inland valleys and 1-1.5 inch for the
coast, Coast Range, and Cascades. This will also be a relatively
warmer system, so snow levels during this time are forecast well
above the Cascade passes (around 6500-7000 ft).

Over the weekend (Sat-Sun), WPC clusters are in agreement that
this robust upper level trough will continue to progress
southeast toward Northern California and the Great Basin. As it
does, additional precipitation will continue through the
weekend. Chances for 48 hr QPF exceeding 1 inch ending 5 AM
Monday are around 40-60% for the Coast Range and Cascades, and
5-10% for inland valleys.

Currently, HEFS guidance shows all rivers across northwest
Oregon and southwest Washington having a less than 5% chance
of reaching action stage. However, we will still continue to
monitor the potential for hydro impacts to our rivers. Flood
control reservoirs are now full for summer water supply, so the
Willamette River can be more susceptible to flooding now. Those
with river interests should continue to monitor the forecast
over the next few days.

WPC cluster analyses are in agreement of additional troughing
over the Pacific Northwest Monday to Tuesday. There still
remains some uncertainty with how strong the troughing will be,
but the majority of ensemble members suggests we`ll maintain a
wet pattern through at least early next week. Don`t put your
rain jacket or rain boots away just yet!           -Alviz

&&

.AVIATION...Mainly non-impactful post-frontal showers this
morning, though they will taper in the afternoon. Satellite shows
some bubbling cumulus east of KPDX with stratus from the Coast
Range westward. Will see some light thinning after 22Z and more
widespread VFR, though some of the drainage airports near rivers
(like KKLS) will remain MVFR during this improvement session.

A warm front will slowly move over the region from the southwest
after 04Z Thursday first impacting the central Oregon coast. There
does appear to be some orographic lift over the Coast Range with
rain shadowing for inland sites north of KUAO. Will see the
lowest CIGs from KSLE southward including KEUG. There is around a
50% chance for near IFR CIGs after 08Z Thursday from KCVO
southward. Because confidence is low, have omitted from the TAFs.
LLWS is not a concerns as winds aloft are unidirectional. After
12Z Thursday, will see a transition to easterly winds through the
atmosphere.

Notes: The ASOS at KTTD is only available via the dial in option.
There is no estimated time of full repair and restoration for
this location.

PDX AND APPROACHES...VFR with a 40% chance of MVFR CIGs based on
high resolution models late (after 06Z Thursday). Because it is a
warm front incoming, have lowered CIGs to high end MVFR levels as
that is a general trend. Rain will be light, with no impacts to
VIS due to a lack of wind. Light winds follow with easterly
winds above 1000 ft AGL while surface winds will be variable.
-Muessle

&&

.MARINE...Active weather pattern continues through the week as
Pacific front move through the waters about once a day, bringing
periods of Small Craft Advisory winds. The next front arrives
tonight and is expected to bring southerly winds gusts to 25 kt,
primarily over PZZ271 and 272. The next front for Friday looks
a little stronger with gusts 20 to 30 kt across most of the zones.
A weaker front follows on Saturday. Seas around 9 ft with a period
around 11 seconds early this morning. Seas will subside to around
4 to 6 ft later today through Friday, then expected inch up to
near 8 ft late in the weekend.-MH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 6 PM this evening to 5 AM PDT
     Thursday for PZZ271-272.
&&

$$

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