140
FXUS66 KPDT 092035
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
135 PM PDT Thu May 9 2024

.SHORT TERM...
Tonight through Saturday night...
A large ridge of high pressure will build over the Pacific
Northwest through Saturday. This ridge will flatten a bit through
Saturday night. Dry and increasingly warm conditions are expected
through the weekend. High temperatures will be 15 to 20 degrees
above normal on Saturday, on average across the area.

Probabilities of high temperatures >=90 degrees on Saturday range
from about 60% in the lower Columbia Basin of Oregon to about 60
to 70% in the Yakima Valley and 70 to 80% in the Columbia Basin of
Washington. None of the GFS ensemble members reach >=90 degrees
on Saturday for Tri-Cities whereas approximately 50% of the ECMWF
ensemble members >= 90 degrees.

High temperatures will range from the upper 70s to mid 80s on
Friday, then generally in the 80s to around 90 degrees on
Saturday. Overnight lows will be in the 40s tonight and the 40s
to lower 50s Friday night.


.LONG TERM...
Sunday through Thursday..A shortwave trough will approach the
area on Sunday and move across the region Sunday night. The
ensemble clusters favor a flat wave compared to the higher
amplitude depicted in the deterministic models. Sunday will be the
last very warm day with high temperatures in the mid 80s to lower
90s in the lower elevations. Probabilities of 90+ degree high
temperatures Sunday are 30-70% across the Columbia Basin and
Yakima Valley. A cold front will cross the area Sunday associated
with the shortwave and it will become breezy through the Cascade
gaps in the afternoon and evening. The winds will continue on
Monday along with cooler temperatures (8-10 degrees cooler than
Sunday.) The 12Z GFS is forecasting the surface pressure gradient
between PDX and GEG to exceed 10 mb on Sunday night and Monday
which supports windy west winds in the lower elevations.
Probabilistic NBM for the 24 hours ending at 11 PM Monday shows a
50-70% chance of winds exceeding 45 mph in the usual windy
locations under strong westerly flow regimes.

On Tuesday into early Wednesday the GEFS and ECMWF ensemble build a
ridge into the region from offshore with NWLY flow aloft over the
area. This will result in dry and warm conditions on Tuesday and
possibly Wednesday though the uncertainty in the forecast begins to
increase on Wednesday and even more on Thursday. For Thursday the
ensemble clusters are split with roughly half the ensemble members
favoring a trough solution and the other half favoring a ridge. This
is creating significant uncertainty in the temperature forecast for
mid week. For example, on Thursday at Pendleton the NBM 25th
percentile high temperature is 66 degrees and the 75th percentile is
85 degrees. The GFS and ECMWF ensemble temperatures are cooler than
the official forecast so it is possible that temperature will have
to be nudged downward in later forecasts. The chance for
precipitation appears quite low through the period. Except for
occasional POPS 15-20% along the Cascade crest, Northern Blues and
Wallowas, the chance for measurable precipitation elsewhere is 10%
or less. 78

&&

.AVIATION...
18Z TAFS...VFR conditions through the period with FEW-SCT cirrus
at 25 kft AGL. Winds this afternoon mainly from the N-NE at 10-15
kt with a few gusts to 20 kt, becoming light terrain driven after
sunset. 78

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  47  79  51  84 /   0   0   0   0
ALW  50  82  54  86 /   0   0   0   0
PSC  52  86  55  91 /   0   0   0   0
YKM  48  85  51  90 /   0   0   0   0
HRI  49  84  53  90 /   0   0   0   0
ELN  49  83  53  87 /   0   0   0   0
RDM  40  78  46  83 /   0   0   0   0
LGD  44  76  49  81 /   0   0   0   0
GCD  43  77  47  81 /   0   0   0   0
DLS  53  86  57  89 /   0   0   0   0

&&

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

$$

SHORT TERM...77
LONG TERM....78
AVIATION...78