599
FXUS66 KPDT 112059
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
159 PM PDT Sat May 11 2024

.SHORT TERM...Tonight through Monday...Satellite imagery this
afternoon is showing mainly clear skies across the region, though
some cumulus fields have managed to develop across areas of the
northeast OR mountains. Temperatures have already managed to climb
into the 80s across many lower elevation locations this
afternoon, with a few more hours of good daytime heating to go.

The upper level ridge of high pressure that has produced these
warm temperatures and clear skies will continue to sit over the
region through tomorrow morning. That means that tonight may be
another great night to watch the aurora, if it does develop again
tonight. Tomorrow morning, the upper ridge will push east as a
shortwave trough slides across the PacNW later in the day.
Afternoon temperatures will decrease 4 to 7 degrees across the
area as the ridge axis shifts east, but still expect mostly upper
70s to 80s in the lower elevations. Surface pressure gradients
will also begin to tighten across the Cascades in response to the
approaching shortwave, resulting in breezy winds 15-25 mph and
gusts up to 45 mph through the Cascade gaps and into the Lower
Columbia Basin tomorrow afternoon.

Sunday night into Monday morning the shortwave trough axis will
quickly move across the PacNW, placing the region under a brief
northwest flow aloft during the afternoon. By the evening hours, a
quick moving shortwave trough will dive across the PacNW. Overall,
these systems will be fairly dry, though global deterministic
guidance and members of the HREF indicate the development of
light, shallow showers across the central WA Cascade crest Monday
morning (confidence 25%). Otherwise, breezy conditions will
continue through Monday, with westerly sustained winds increasing
to 20-30 mph with gusts up to 45mph through the Cascade gaps and
into the OR Columbia Basin; winds will be 15-25 mph everywhere
else. Winds will be the strongest through the Kittitas valley
Monday, with sustained winds of 25-35 mph and gusts up to 50 mph
developing in the afternoon (confidence 60%). Lawhorn/82

.LONG TERM...Tuesday through Saturday...Deterministic models and
ensembles are in good agreement on the longwave pattern for Tuesday
and Wednesday which provides high confidence in the forecast. An
upper level ridge will be positioned off the west coast with
northwest flow aloft over the region. It will be dry and warm but
not as warm as this weekend. The NBM has high temperatures in the
mid 70s to lower 80s in the lower elevations on Tuesday and mostly
80s on Wednesday. On Wednesday night there will be a 15-30% chance
of light showers along the Washington Cascade crest.

Beginning Thursday through Saturday confidence in the forecast
decreases. The ensemble clusters are split between a trough and
ridge over the area and the GEFS and ECMWF 500 mb ensemble means
show NW flow aloft with a tight 500 mb height gradient across the
Pacific NW. The deterministic models are similar to the ensemble
means. The NBM during this time period shows cooler air filtering
into the region with high temperatures lowering into the mid 60s to
mid 70s for the lower elevations on Friday and Saturday. This lends
credence to the GFS solution which shows a cold frontal passage on
Thursday and a surface pressure gradient of up to 14 millibars
between Portland and Spokane. Pressure differences this high favor
strong and gusty west winds across the lower elevations especially
the Cascade gaps. The NBM probabilities of 45+ mph winds are 40-70%
across much of the lower elevations for Thursday evening/night.

Thursday through Saturday there will be a 10-20% chance of light
showers along the Cascade crest and over the northeast mountains
with snow levels 5000-7000 feet. The probability of thunderstorms in
these areas will be quite low (5-10%). Elsewhere the probability of
measurable rain will be 5% or less. 78


&&

.AVIATION...Previous Discussion...18Z TAFs...Clear skies for all
sites for the next 24 hours. Winds terrain driven and generally
less than 10 kt except for 10G20kt at KDLS, KRDM and KBDN this
afternoon and early evening. 78


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  53  82  51  75 /   0   0   0   0
ALW  58  85  54  78 /   0   0   0   0
PSC  58  89  56  82 /   0   0   0   0
YKM  53  86  51  79 /   0   0   0   0
HRI  57  87  54  80 /   0   0   0   0
ELN  52  81  47  71 /   0   0   0   0
RDM  45  77  43  74 /   0   0   0   0
LGD  51  79  46  73 /   0   0   0   0
GCD  46  80  45  75 /   0   0   0   0
DLS  56  84  53  74 /   0   0   0   0

&&

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

$$

SHORT TERM...82
LONG TERM....78
AVIATION...78