447
FXUS66 KPQR 012222
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
322 PM PDT Wed May 1 2024


.SYNOPSIS...Another system will spread relatively light rain
across the area this evening into Thursday morning, with another
round of light snow for the Cascade passes. Heavier rain arrives
Friday into Saturday, but do not expect any widespread
hydrological concerns at this time. Cool, wet, unsettled weather
likely continues through the middle of next week.

&&

.SHORT TERM...Through Saturday Night...Visible satellite shows
overcast skies across most of northwest Oregon and southwest
Washington this afternoon as high level cloud cover streams over
the region ahead of the next system, helping to hold daytime
highs down in the mid to upper 50s again across the area.
Speaking of the next system, the latest in a series of shortwave
troughs is apparent west of Vancouver Island on water vapor
imagery, with a warm front extending southeastward towards the
Oregon coastal waters from an attendant surface low. Light rain
associated with this front will spread across the area later
this evening from northwest to southeast and continue overnight
as the upper wave crosses overhead. QPF amounts remain rather
modest with this system ranging from a half to a quarter inch
across most of the area through Thursday morning, with generally
less than two tenths along and north of a Hood River-Portland-
Astoria line. The heaviest precipitation amounts will be
focused along the central Oregon Casacdes which could see
0.75-1.00" through Thursday morning. Snow levels remain around
4000 feet, with roughly 2-4 inches of fresh snow expected at
pass levels and locally higher amounts above the passes. Expect
another brief dry spell Thursday afternoon into early Friday as
transient high pressure builds in behind the departing system.
This should allow high temps to climb into the 60s for most
inland locations on Thursday.

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. QPF values
remain on track from the previous forecast, bringing 1.00-1.50
inches through Saturday afternoon in the interior lowlands,
1.5-2.0" along the coast and in the mountains, and locally
upwards of 2.5-3.0" in a few favored spots. 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 CA border. So despite the impressive QPF amounts
for this time of year, this should help to limit hydro concerns
across the area as HEFS probabilistic guidance keeps the chance
of even reaching action stage below 5 percent 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 6000 feet. If nothing else, could
certainly see some local ponding of water in prone areas from
late Friday into early Saturday. /CB

.LONG TERM...Sunday through 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 the end
of the period. /CB


&&

.AVIATION...Warm front is slowly inching eastward this afternoon
with the cirrostratus shield moving over the region. This shield
can be seen in satellite imagery and is the initial portions of
this front. Through the afternoon, precipitation chances will
increase though clouds will see limited changes through inland
locations. Going to see mostly low end VFR conditions as the upper
level clouds will insulate enough that lower clouds will struggle
to form. Onshore winds along the coast will increase though not
looking at any winds above "normal" for the coast during a rainy
pattern.

Rains will be the most predominate between 07-14Z Thursday with
the strongest rain from KSLE southward, along the Coast Range, and
the coastal terminals. VIS may be difficult in some circumstances
- especially when wind are stronger and rain is heavier. Overall
though, looking at generally unremarkable flight conditions
inland, with degraded CIGs along the coast. Do note though that
along the mountains, snow is still possible.

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 little change in the overall
forecast. There is still around a 40% chance of MVFR CIGs between
10-16Z Thursday. However, because of pattern recognition and how
warm fronts tend to behave, have decided to drop CIGs into upper
level MVFR category (around 2900-3500 ft) to account for the
periods of lower CIGs with rain. Bit of a rain shadow so rain will
be minimal with very little impact to flight conditions.
-Muessle

&&

.MARINE...The warm front is moving near the waters this afternoon
and should begin impacting the south-central waters over the next
few hours. Winds will be the main impact as they transition to the
south with the passage of the front. Winds will generally be 5 to
10 kt with gusts to 15 kt. Behind the front, the pressure gradient
will increase and winds will become easterly. Could see higher
wind speeds through the coastal gaps and Columbia River Bar early
Thursday morning but will be marginal for small craft speeds.
Have maintained the advisory though. Seas will not be impacted by
the winds, and in fact could see lower wind waves due to the
offshore winds.

The next impactful event arrives early Friday. This low pressure
system and associated front appear to be much more robust -
though there is ample time for it to change. Seas will build and
winds will increase. Not seeing gale force winds, or combined seas
exceeding 10 ft though. -Muessle



&&

.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.
&&

$$

www.weather.gov/portland

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