Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 170531
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1031 PM PDT Sat Mar 16 2024

Updated Aviation Discussion

EVENING UPDATE...Satellite imagery tonight continues to show
decks of cirrus from the northeast pushing across eastern WA/OR.
Overhead, an upper level ridge of high pressure will continue to
bring dry and warming conditions across the region tomorrow. Winds
will generally be light throughout the day, but periodic locally
breezy conditions may develop in the afternoon. Afternoon
temperatures will continue to warm another 2 to 6 degrees
tomorrow, with highs in the upper 60s to low 70s across the lower
elevations...50s to low 60s in the mountains. Lawhorn/82

AVIATION...06Z TAFS...VFR conditions will prevail through the
period. Few to Sct decks of cirrus AOA 25kft AGL will stream
across sites throughout the period, though mostly clear skies are
expected. Winds will be light, less than 12kts, and terrain driven
through the period. Lawhorn/82

PREV DISCUSSION... /issued 418 PM PDT Sat Mar 16 2024/

.SHORT TERM...Today through Monday night...Current radar and
visible satellite imagery showing dry conditions as a thin veil of
cirrus nudges into our eastern zones. Noon temperatures have
broken into the 60s across lower elevations of the Basin, as highs
are expected to peak in the mid-to upper 60s. Confidence in these
high temperatures is high (90-100%) as the HREF showcases a 60-80%
of high temperatures of 65 or greater at the Dalles, Yakima,
Hermiston, and the Tri-Cities.

These warm and sunny conditions are a result of a Rex Block as a
strong area of high pressure, located over the Pacific Northwest,
continues to dominate the weather pattern into the beginning of
the workweek. This will keep temperatures warming 2 to 6 degrees
each day, as high temperatures reach into the upper 60s to low 70s
Sunday and into the low to mid-70s on Monday across the Basin,
Central Oregon, Blue Mountain foothills, and the Yakima/Kittitas
Valleys. Confidence is low to moderate (30-60%) in high
temperatures reaching into the 70s across lower elevations of the
Basin on Sunday, as the NBM highlights a 30% to 54% chance of high
temperatures reaching 70 degrees or higher in these areas.
Confidence is moderate to high (60-80%) in highs reaching 70
degrees or higher across lower elevations of the Basin, as the
NBM showcases a 54% to 73% chance of 70 degree highs for Hermiston
(64%), Tri-Cities (54%), Yakima (56%), and the Dalles (73%). At
this time, temperature records are not in jeopardy of being
reached or broken through Monday, with Monday`s forecast highs
currently 4 to 8 degrees below current records. However, they may
come close as guidance has ran slightly cooler over the previous
days.

The Rex Block begins to break down on Monday as a weak shortwave
rides over the flow across northern British Columbia and a upper
level trough slowly propagates into the eastern Pacific. Clear
skies, calm winds, and drying conditions will ensue into the early
part of the workweek before the next potential system arrives
well into the extended period. 75

.LONG TERM...Wednesday through Saturday...An upper-level ridge
continues passing over the PacNW Tuesday morning until entering a
zonal pattern by Wednesday into Thursday morning due to being in
between systems. Winds will become moderate for Tuesday night into
Thursday morning with a chance of wind gusts between 20-30kts in
the Simcoe Highlands and Oregon Cascades, spreading out to most
of the forecast area except Blue Mountains by Wednesday night.
Both ECWMF and GFS show dry conditions Tuesday morning into
Tuesday night when the ECWMF becomes slightly wetter than GFS.
Precipitation increases by Wednesday morning into Thursday within
the ECWMF but dries sooner for GFS. Fair agreement with the
ensemble means and deterministic models on the amplitude of the
ridge and a zonal pattern (50-60% confidence). Tuesday night and
Wednesday, ensembles clusters show more uncertainty in the 500 mb
pattern, solutions ranging from a persistent upper-level ridge
(25% of members) to a trough (26% of members).

The multi-model ensemble mean suggests a flattening of the upper-
level ridge, but smooths the details of the individual cluster
scenarios. Worth noting, the primary source of variance (36%) among
ensemble members is the amplitude of the 500 mb heights over WA/OR.
Confidence lowers due to this difference along with timing of dry
conditions (40%). Confidence is high that temperatures remains above
normal with high EFI of 0.7-0.95, showing an anomalous event for
maximum temperatures within the forecast area on Tuesday (90%
confidence). Snow levels will be upwards to 6900-7400ft by Tuesday
morning and will decrease around 4700-7000ft Wednesday morning and
3000-5000ft Thursday morning while PacNW enters a zonal pattern.
Feaster/97

Thursday through Saturday...Ensemble and deterministic
models are suggesting a semi-active pattern through the period, with
greatest precipitation chances (55-75% for the mountains and
foothills, and 20-40% for the lower elevations) Friday and Saturday.
Ensemble clusters reveal differences in the phase of the 500 mb
heights over the PacNW Thursday and Friday (20% chance of an
anomalous ridge centered overhead, 36% chance of some flavor of a
shortwave trough, and 34% chance of the ridge axis shifted east over
the northern Rockies/High Plains). Of note, 47% of ensemble variance
is accounted for by the difference in 500 mb heights overhead.
Ensemble agreement in a trough increases Friday afternoon through
Saturday for the PacNW (~75% chance), but details on timing and
amplitude remain unclear.

Regarding tangible differences in weather for the scenarios, expect
a warmer, drier pattern should the ridge persist, and cooling with
the aforementioned chances of measurable precipitation in the ridge
breakdown/troughing scenario.

The ECMWF EFI does not highlight any good ensemble agreement in
unusual temperatures, precipitation, or wind. Plunkett/86

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  38  66  40  70 /   0   0   0   0
ALW  42  67  45  72 /   0   0   0   0
PSC  41  70  44  73 /   0   0   0   0
YKM  38  71  41  72 /   0   0   0   0
HRI  40  70  42  73 /   0   0   0   0
ELN  39  69  40  70 /   0   0   0   0
RDM  31  66  34  72 /   0   0   0   0
LGD  37  67  38  70 /   0   0   0   0
GCD  36  69  37  71 /   0   0   0   0
DLS  43  72  44  75 /   0   0   0   0

&&

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

$$

EVENING UPDATE...82
SHORT TERM...75
LONG TERM....86/97
AVIATION...82


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