772
FXUS66 KPDT 020507
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1007 PM PDT Tue Apr 1 2025

.Updated for Aviation...


AVIATION...
06Z TAFS...Shower activity continues to decrease. VFR conditions
are expected for the most part, though MVFR CIGS can not be ruled
out at BDN or RDM. For now, have both sites going down close to
MVFR but maintaining VFR conditions. Most of the guidance keeps
VFR, though some guidance suggests MVFR. Confidence is 33% or
less, but its possible especially toward daybreak.

Otherwise, gusty winds to around 25 kts are expected at PDT and
DLS from late morning through the afternoon hours. The rest of
the TAF sites should have winds 10 kts or less.


&&

.PREV DISCUSSION... /issued 516 PM PDT Tue Apr 1 2025/

Updated for Aviation...

AVIATION...
00Z TAFS...Latest radar showed isolated showers across the area.
These showers are expected to decrease in coverage this evening.
While almost any site could get a passing shower, included in the
locations that seemed most likely during the early evening.

Otherwise, winds could get gusty around any heavy showers,
otherwise will generally be 10 kts or less except at PDT, DLS and
ALW where there will be some gusty winds in the 20 to 25 kt range
at DLS and PDT this evening and around 15 to 20 kts at ALW. Winds
will gust again Wednesday afternoon at these locations.

PREV DISCUSSION... /issued 257 PM PDT Tue Apr 1 2025/

SHORT TERM...Tonight through Thursday...

Radar currently shows scattered to isolated showers developing
through the Columbia Basin. No lightning currently associated with
these pockets of precipitation, but current instability values
shows a few pockets of 500 J/kg of CAPE in the CWA. This along
with some break in the clouds could fuel some isolated
thunderstorms to develop later in the afternoon (10-30% chance).
Rain across the Basin will taper off as we head into the late Tue
PM hours and into the overnight. A few areas of light mountain
snow in the Cascades and Blue Mountains that will continue through
tonight as the trough continues southeastward. Had to adjust
Bend/Redmond highs and lows slightly lower for the next 24 hours
to account for the brief snowfall that occurred earlier this
morning.

As rain dries out of the Basin, light mountain snow will remain
throughout all mountain regions as the upper ridge continues to
move into the region. Guidance for additional snow accumulations
is suggesting up to 3" of additional mountain snow (including the
passes) with a 70-80% confidence. Mountain snow will clear up by
Thursday morning, but model guidance is a bit divisive if it
wants to give the Northern Blue Mountains a brief second round of
snow or rain in the afternoon hours of Thursday. About 57% of
clusters are projecting a brief period of rain before the ridge
takes over the pattern and dries out any precipitation for the
remainder of the short term.

Winds aloft will have a more northward nature by Thursday evening,
dropping any remaining precip chances area wide, making way for a
warmer trend to commence shortly after. Winds across the region
will be breezy with most areas of Basin gusting up to 15 to 25
knots with mostly west/west- northwest predominately surface
winds with a decrease in strength at night time hours.

LONG TERM...Thursday night through Tuesday...

Key Messages...

 - Drying and warming trend peaking Sunday with highs 10-15 degrees
above average.

 - Unsettled conditions with light precip chances late Sunday into
Tuesday, mainly in the mountains.

The large scale pattern early Thursday will be characterized by an
amplified, deep synoptic heights with an upper-level ridge offshore
the West Coast into Yukon and deep upper-level troughs upstream and
downstream, the latter extending across the Canadian Prairies into
the Four Corners region. The pattern will be fairly progressive day
3 to day 7 with upper ridging promoting drying and warming through
the weekend until near seasonable temperatures and low chances
return Monday-Tuesday, mainly in the mountains. Overall, guidance in
fair agreement with increasing uncertainty revolving around a
shortwave trough and its amplitude Sunday-Monday. Guidance support
anomalous upper ridging building Friday still offshore before moving
into the PacNW and British Columbia Saturday. Of which, forecasts
show the highest heights above average for this time of year across
BC into the Northwest Territories with EPS mean 500 hPA heights
forecast to exceed model climate for this time of year. Meantime,
start to see 850 hPa temperature anomalies +7C across the Interior
NW as warmer air mass takes hold under southerly flow this weekend
peaking on Sunday. That said, not atypical with highs forecast 10-15
degrees with the greatest departure from average on Sunday. This is
supported with only a minor signal in the Extreme Forecast Index
only showing limited areas of 0.5-0.6 indicative of high but not
unusual temperatures forecast by the EPS, that increases confidence
in the forecast and magnitude of the highs with them not being
atypical.

Looking ahead, clustering scenarios show an upper trough building in
the eastern North Pacific with a shortwave trough ejecting into the
Pacific NW and likely crossing Monday though differences in strength
and timing are apparent. Current thinking is the front will be
somewhat weak with its attendant moisture plume largely out of the
SSW with a trajectory favoring the OR/WA Cascades, and not so much
the eastern mountains. Further, the plume shows limited IVT to work
with limited probs in excess of 150 Kg/ms seen via the inland
transect of the foothills of the Cascades (~60-70%) and less in the
inland transect (40-60%).  As such, the combination of weak forcing
and a less favorable pathway seems conducive for limited mountain
accumulating precip, mainly in the form of high mountain rain with
snow levels above 5 kft forecast through Sunday night before falling
some Monday. Latest QPF clusters show increasing chances with the
most likely scenario (~60%) for precip to be confined to the upper
slopes of the eastern Cascades through Sunday night. With the best
chances for lowlands and eastern mountains to see any rain falling
more so in the window of Monday-Monday night. Meantime, with the
weak frontal passage, expect highs to fall closer to near average
Monday and Tuesday. Otherwise, winds look largely light in the long
term except for breezy conditions Monday-Tuesday. Current thinking
is peak daily gusts in excess of 25 mph is likely (60%) across much
of the lower elevations on Monday.

AVIATION...18Z TAFs...Latest aviation concerns revolve around a)
ongoing snow showers in central OR, b) afternoon rain shower chances
with a low chance of thunder this afternoon, and c) possibly sub-VFR
late tonight. Latest radar and satellite depicts some isolated light
rain showers across south central WA and area of light snow across
KBDN. Both should lessen in coverage and diminish between now and 20
UTC before renewed isolated-widely scattered showers develop this
afternoon. Latest HREF guidance and marginal instability support a
risk for thunder (10-30%) outside our TAF terminals across the
eastern mountains. Otherwise, these shower chances will diminish in
the evening with loss of daytime heating. The other concern is
potential for stratus to build into central OR overnight-early
morning tomorrow with sub-VFR ceilings looking more likely than
not.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  36  55  34  57 /  30  10   0  10
ALW  38  54  36  55 /  30  20  10  20
PSC  35  60  35  61 /  20   0   0   0
YKM  33  58  32  60 /  10   0   0   0
HRI  36  58  35  60 /  30   0   0  10
ELN  35  54  35  57 /   0   0   0  10
RDM  26  50  26  52 /  20   0   0   0
LGD  32  48  28  49 /  30  20  10  20
GCD  31  46  27  48 /  60  20  10  10
DLS  39  57  37  61 /  20  10   0   0

&&

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

$$

SHORT TERM...95
LONG TERM....80
AVIATION...77