317
FXUS66 KPDT 041114
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
414 AM PDT Fri Apr 4 2025


.UPDATED AVIATION...12Z TAFS...All sites will begin in VFR and
remain so for the remainder of the period. VIS and CIGs remain
elevated and winds remain light and variable for the period with
sustained up to 12 knots. No precipitation forecasted for this
period thanks to ridging taking course for the region.

&&

.PREV DISCUSSION... /issued 332 AM PDT Fri Apr 4 2025/

SHORT TERM...Today through Sunday Night...

Key messages:

1. A ridge will bring fair and dry weather with warming conditions
today through Saturday night

2. A trough will push the ridge east out the area Sunday and a
front will arrive Sunday afternoon and night bringing up to a
quarter inch of rain after midnight Sunday night.

Satellite imagery shows a large upper low in the Gulf of Alaska
which is building a ridge ahead of it in the eastern Pacific. This
ridge is still offshore and the satellite imagery shows a
northerly flow over the Pacific Northwest early this morning. The
ridge will slowly move ashore and cross the area through Saturday
night which will give us a couple of days of dry and warming
conditions. By Sunday, the ridge will be moving off to the east
and will be replaced by an upper trough. The trough will be
sending a system ashore and into our area Sunday afternoon and
night with rain developing in the late afternoon and becoming
heavier overnight. The Extreme Forecast Index indicate little in
the way of unusual weather through Saturday night then highlights
temperatures Sunday and Sunday night with values around 0.85. It
also highlights QPF Sunday night with a value of 0.76 focused on
the Cascades, Columbia Basin and Blue Mountain Foothills with a
Shift of Tails over the eastern portion of the Columbia Basin and
the Blue Mountain Foothills, which suggests some ensemble members
hinting at more extreme amounts of QPF. A closer look at QPF in
model clusters show that the possibility of higher QPF is fueled
entirely by the GFS model with no support at all from the ECMWF
and Canadian. Overall forecast confidence is excellent through
Saturday night then drops to good Sunday and Sunday night.

Today will see sunny skies with temperatures warming 6 to 8
degrees from yesterday with highs in the upper 50s to mid 60s and
in the mid 40s to mid 50s in the mountains. Do have some concerns
that temperatures might be a bit too warm in the Wallowa Valley
due to some snow from last evening remaining on the ground, though
left temperatures unchanged from the NBM as the snow should melt
this morning and be gone by the afternoon. Winds will be less than
10 mph from the east to northeast. Tonight will see continued dry
conditions and with the ridge building overhead, temperatures
will be up 2 to 5 degrees with lows in the mid 30s in the Columbia
basin and in the mid 20s to mid 30s elsewhere.

Saturday will see the ridge axis crossing the Cascades in the
afternoon though skies will be partly cloudy instead of sunny.
Temperatures will warm further with highs in the mid to upper 60s
in the lower elevations and in the 50s and lower 60s in the
mountains. With the ridge overhead and continued partly cloudy
skies, overnight lows will be up a few degrees to the mid to
upper 30s in the Columbia Basin and in the mid 20s to mid 30s
elsewhere.

Saturday night the ridge will move east out of the area and the
trough will push ashore Saturday evening then cross the Cascades
into our area late Sunday afternoon and spread across the area
Sunday night. A southwest flow ahead of the front will warm
temperatures Sunday another 5 or so degrees to the upper 60s to
mid 70s in the lower elevations and into the lower to mid 60s in
the mountains. With the approaching system, skies will become
cloudy through the day and the Cascades will see a chance of rain
developing with snow levels at 6000-7000 feet. The entire area
area will develop a chance of rain Sunday night. Rain will be
heaviest in the overnight hours with around a quarter inch in the
mountains, one to two tenths of an inch in the Blue Mountain
Foothills and less than a ten of an inch elsewhere. Perry/83

LONG TERM...Monday through Friday Night...

Key messages:

1. Light Mountain Snow/Low elevation rain to start the period.
2. Multiple systems with a slight break on Tuesday.

Models paint a confident picture to start the long term with the
overhead ridge that provided us with dry weather will promptly exit
the region. The long term will begin with an area of troughing and
increased PoP chances area wide. Southwest flow will predominately
cover the area, increasing moisture advection with mountain snow and
chances of rain in low elevations. Snow levels will drop from 6000-
6800 feet to 4500-5000 feet as the area of troughing enters the
region. Areas around the Blue Mountains will see a delay of snow
level dropping later in the day Monday. Snow accumulations for this
period don`t seem impressive with most of the precip accumulations
up in the Cascade crests. NBM only forecasts up to 0.50" for most
parts of the Cascades and up to 0.10" for parts of the Blues (30-50%
confidence for both totals).

Heading into Tuesday morning, slight ridging will clear up the
region for a few hours, before troughing again dominates the upper
air pattern. Still some slight disagreements among the clusters as
how much of the CWA will dry out due to some fluctuations with how
strong/weak it wants to bring that slight ridging. Of the clusters,
23% wants to bring a weaker ridge with only small parts of the Basin
drying out before the second round of weather, but 23% want to
strengthen the ridge and bring more widespread drying. All clusters
do eventually bring back the precipitation by Tuesday evening (60-
80% confidence).

Ridging begins to build and amplify from the California/Arizona
southwest region up towards the PacNW area. This will naturally
bring our precipitation chances down across the board. Clusters have
a good handle to bring ridging in the region, but the number one
discrepancy will be the strength and amplitude of the system. 46% of
clusters would like to amplify the ridge stronger than the other 54%
and dry out the CWA by Wednesday evening. Heading from Wednesday to
Thursday morning, 54% of clusters would keep our area dry, while 46%
like to keep the lingering showers/light mountain snow in the
Cascades through the day. Snow accumulations will be brief and not
impressive with snow levels in the 4000-5500 feet range. The vast
majority of clusters will bring back low level rain/light mountain
snow for Friday through Fri evening hours due to another trough
system entering from the pacific. Some models hinting the snow
reaching Central OR (23% of members) but any amounts will likely not
be more than an inch in those areas (30-50% confidence). Clusters
get very unreliable this far out with timing/strength not in good
agreement.


PREV DISCUSSION... /issued 1015 PM PDT Thu Apr 3 2025/...

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  61  35  67  42 /   0   0   0   0
ALW  60  37  65  43 /   0   0   0   0
PSC  64  34  68  40 /   0   0   0   0
YKM  63  36  65  42 /   0   0   0   0
HRI  64  34  69  40 /   0   0   0   0
ELN  61  35  64  41 /   0   0   0   0
RDM  61  30  69  37 /   0   0   0   0
LGD  57  31  62  37 /   0   0   0   0
GCD  56  31  64  37 /   0   0   0   0
DLS  67  39  69  45 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...83
LONG TERM....95
AVIATION...95