Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 292323
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
423 PM PDT Fri Mar 29 2024

Updated aviation discussion

.SHORT TERM...Tonight through Sunday night...Little to no
seasonable weather impacts through the weekend. The main
highlights are light rain showers possible today-early tonight
(10-50%) outside of Lower Basin, north central OR, and south
central WA; dry conditions this weekend; and start of a warming
trend.

Latest day cloud phase RGB imagery shows a mix of liquid topped cu
and glaciating towering cu from south central OR into the eastern
mountains, a few swaths of thin high clouds drifting across
eastern OR, and lower sky cover of few-scattered cu across parts
of south central WA. Local radar display shows some weak returns,
25-35 dBZ, indicative of some light showers across the eastern
mountains. These showers extend down into the central OR
mountains, albeit the radar beam overshooting there but
precipitation and virga is evident on some web cams and confirmed
by obs. The latest water vapor imagery shows an impressive upper
low offshore northern CA that is elongating the upper trough that
extends across the PacNW to offshore CA. This closed low will
continue to evolve and drop southward through tomorrow. This
feature is providing some limited wrap around moisture in tandem
with weak forcing for ascent that is helping support these
showers. The latest mesoanalysis shows limited instability in
place and this should lower our lightning risk for this afternoon.
Overall, anticipate scattered coverage over the eastern mountains,
central OR on west into the central OR Cascades based on satellite
trends and latest hi-res guidance. Precip type should be mainly
rain except for in the high mountains today/early tonight based on
obs with temps in the 30s to lower 40s between 5-6 kft right now.
High confidence (>80%) in light rainfall amounts under a tenth of
an inch for most, except for parts of the central OR mountains and
east slopes of the central OR Cascades. Of which, HREF LPMM
depicts a reasonable high-end of a tenth to a quarter inch. That
said, chances for exceeding a tenth or more generally under 25% in
these areas. Thus little to no impact from these showers
anticipated.

Northerly flow will be well established overhead by Sunday as the
large scale pattern becomes more amplified. Guidance in good
agreement with the upper trough extending south near Baja
California by Sunday with an modest upper-level ridge upstream in
the eastern North Pacific extending into British Columbia.
Generally dry conditions expected tomorrow through Sunday night,
though a weak disturbance embedded in the upper-level flow is
expected to drop into the Northern Intermountain West on the
eastern periphery of the ridge Saturday night. This should
translate just to some increased sky cover Saturday night but
there may be sufficient residual moisture to support very low
chances in the northern Blues and Wallowas Sunday (chances 15% and
less). Highs will be gradually warming each day with highs Sunday
in the Lower Basin into the foothills of the Blues around 5-7
degrees warmer than today.

.LONG TERM...Monday through Friday...Models in pretty good agreement
through the period, except for Wednesday. Cluster analysis shows the
greatest discrepancy Wednesday with 57% of the members keeping the
upper trough off the coast for another 12-18 hours while 43% of the
members show it moving onshore or over the area. The ensembles are
in good agreement showing the upper trough not moving onshore until
Wednesday night into Thursday. If this pans out, Wednesday should be
only 4-8 degrees cooler than Tuesday given more cloud cover with the
dramatic temperature decrease holding off until Thursday. In
addition, the temperature spread for PDT on Wednesday is
considerable with lower 50s to mid 70s which shows the uncertainty
for this time period. This is also true for other locations
throughout the Columbia Basin and Blue Mountain Foothills. Models
lately have trended towards a "slower solution" with ridge breakdown
so will go above NBM`s dramatic cooling for Wednesday blending more
towards Tuesday`s temperatures for the Columbia Basin and Blue
Mountain Foothills. The EFI shows a potential for breezy conditions
Wednesday and Thursday, but this may be more like Wednesday night
into Thursday if things slow down. EFI also shows unusually warm
daytime highs for Monday through Wednesday. The pattern is expected
to get active again as an upper level trough makes its home over the
Pacific Northwest Thursday and Friday. However, much of its energy
will move into northern California and southern Oregon as the low
cuts off from the main flow. 24 hour QPF totals of greater than 0.20
inches remain confined to the mountains with probabilities in the 50-
75% range, mainly Cascades. Central Oregon`s best chance (40-50%) of
a wetting rain will be Thursday as the low splits and moves
southward. The Washington side will see less impacts from this
system.

Daytime highs will be well above normal Monday through Wednesday
with the warmest day expected to be Tuesday. Would not be surprised
if a few records are tied or broken. A strong cold front will cause
a dramatic temperature drop for Thursday. Temperatures will remain
below normal through the rest of the extended period. Earle/81


&&

.AVIATION...00Z TAFs...VFR conditions will prevail through the
period with some lingering showers through the evening impacting
RDM, BDN and PDT. Otherwise mostly clear skies and winds of 5-15kts.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  33  56  33  58 /  10   0   0   0
ALW  34  60  35  61 /  10   0   0  10
PSC  37  64  37  66 /   0   0   0   0
YKM  32  63  33  66 /   0   0   0   0
HRI  34  62  35  65 /   0   0   0   0
ELN  31  60  34  63 /   0   0   0   0
RDM  31  54  27  55 /  30   0   0   0
LGD  33  56  30  54 /  10   0   0   0
GCD  32  54  28  53 /  60   0   0   0
DLS  38  64  38  66 /   0   0   0   0

&&

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

$$

SHORT TERM...80
LONG TERM....81
AVIATION...81


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