946
FXUS66 KPQR 020955
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
255 AM PDT Thu May 2 2024

.SYNOPSIS...Another system will bring rain and Cascade snow
(above 4000 ft) this morning. Expect conditions to dry with
some clearing skies by this afternoon. Heavier rain arrives
Friday into Saturday, but we are not expecting any widespread
hydrological concerns at this time. Cool, wet, unsettled
weather likely continues through the middle of next week.

&&

.SHORT TERM...Thursday through Saturday...Mesoanalysis as of
245 AM PDT depicts a 1013 mb low pressure system centered off
the north Oregon coast. This low is currently progressing
southeast, bringing a band of light to moderate rainfall across
northwest Oregon and southwest Washington. Based on webcams,
snow is beginning to fall in the Cascades. The very marginal
Winter Weather Advisory remains in effect for the North Oregon
Cascades, and the Marion, Linn, and Lane County Cascades through
11 AM PDT today. Expect around 2-6 inches of snow this morning
above 4000-4500 feet, with heavier snow above 5000-5500 feet.

For everyone else, the heaviest rain amounts this morning will
be south of a line extending from Astoria-Portland-Hood River.
Locations such as the central Oregon coast, central Oregon Coast
Range, and central/south Willamette Valley are forecast to
receive an additional 0.25-0.40 inch of QPF this morning. Along
and north of the Astoria-Portland-Hood River line, precip
amounts will generally be less than two tenths of an inch. The
bulk of the precipitation will end no later than mid-morning
today (8-10 AM) as this system quickly exits and weakens to the
southeast. Expect predominately dry conditions by this afternoon
with a bit of sunshine as transient high pressure builds aloft.
This will allow today`s afternoon high temps to climb into the
60s for most inland locations.

The more active weather arrives Friday afternoon as a much
deeper trough drops out of the Gulf of Alaska and sends a
stronger front across the area Friday into early Saturday.
Expect heavier rainfall to accompany this system as IVT values
briefly max out around 250-400 kg/ms Friday evening, with
precipitable water values around 1 inch running two standard
deviations above normal by early May standards. There have been
minimal changes to the QPF forecast, with 1-1.5 inches for the
interior lowlands, and 1.5-2 inches for the coast and mountains
from late Friday morning to Saturday afternoon. Winter weather
impacts are not expected for the Cascade passes on Friday as
snow levels will be rising above 7000 feet.

Fortunately, the system looks to move through rather quickly
with rain tapering off to showers by Saturday evening as the
low dives south towards the OR/CA border. Snow levels will drop
back down to 3500-4500 feet by late Saturday morning, returning
snow to the Cascade passes. The latest NBM suggests a 40-60%
chance of 6 inches of snowfall or greater in a 24 hr period
ending 5 AM Sunday. Another Winter Weather Advisory is starting
to look more likely for Saturday.

Despite the impressive QPF amounts for this time of year, the
fast progression of this system should help limit hydro concerns
across the area. We could see a slight uptick in river levels,
however, HEFS probabilistic guidance still keeps the chance of
reaching action stage below 5-10% on all area rivers. That said,
the system will still bear watching into the weekend given that
area reservoirs are close to full and snow levels will be rising
above 6500-7000 feet on Friday. If nothing else, we could certainly
see some local ponding of water in prone areas from late Friday
into early Saturday.        -Alviz/CB

&&

.LONG TERM...Saturday night to Wednesday...Expect an active,
cool, and showery pattern to persist into the middle of next
week as WPC ensemble clusters continue to show general agreement
on some semblance of upper level troughing remaining over the
Pacific Northwest through Wednesday. Do not see any signals for
particularly notable QPF in any one period beyond Saturday, but
area rivers will likely continue to run high for this time of
year as episodic bouts of rain continue across the region.
Temperatures will continue to run a bit below normal, with
daytime highs struggling to get out of the 50s through
Wednesday. Will note that clusters do start to show a high
pressure ridge building over the NE Pacific on Wednesday. If
this ridge ends up moving eastward, then we could potentially
see a pattern shift towards drier and warmer weather by late
next week.      -Alviz/CB

&&

.AVIATION...Surface low moving to the central coast, should make
landfall by 12Z Thu. Light rain across the area with a mix of VFR
to IFR/LIFR conditions. IFR/LIFR tends to be on the central Oregon
coast near the low, and inland towards the coast range where
upslope winds tend to create lower cigs.

Around 14z Thu, the low pushes through, and ceilings will slowly
improve back to VFR over the following few hours. Guidance shows a
north to south progression of improving conditions. Winds will be
fairly light at almost all terminals throughout the TAF period,
with the exception of KONP, which could see some southerly gusts
up to 20kt accompanying the frontal passage by 12Z Thu. Effects
from the next front starts towards the end of the TAF period,
bringing more rain and lowered cigs.

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...A mix of VFR and MVFR expected over trough
about 12-14Z per HREF guidance, then trending toward VFR through
12Z Fri. However depending how much clearing occurs, low stratus
or fog may form in the area. HREF showing around 10% chance for
IFR conditions after 09Z Fri.    /mh

&&

.MARINE...Surface low over the central coastal waters will continue
to slide southeast and make landfall by sunrise. South to
southeast winds gusting 20-25 kt south of about Lincoln City with
easterly winds to the north, but weaker. The low will continue
to weaken today as will winds. High pressure builds offshore
resulting in northerly wind developing later in the day.

The next impactful event arrives early Friday. This low pressure
system and associated front appear to be much more robust, so have
issued a Small Craft Advisory for the outer zones, PZZZ
271,272,273, from Friday morning through early evening with gusts
20 to 30 kt. Lower forecast confidence for the inner zones with a
20-50 percent chance for gusts above 21 kt. Will see which way
models trend to decide on issuing an advisory or not.

Seas starting out around 4 ft this morning but looks to remain
below 10 ft through the weekend and early next week.    /mh

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Weather Advisory until 11 AM PDT this morning for
     ORZ126>128.

WA...None.
PZ...Small Craft Advisory until 5 AM PDT early this morning for
     PZZ271-272.

     Small Craft Advisory from 8 AM to 8 PM PDT Friday for PZZ271>273.
&&

$$

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