761
FXUS66 KPDT 052041
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
141 PM PDT Wed Jun 5 2024

.SHORT TERM...Tonight through Friday...Mostly clear skies have
developed across the intermountain PacNW this afternoon, with
light winds and temperatures in the upper 60s to lower 70s. This
quiet pattern is thanks to an upper level ridge that has begun to
build into the PacNW from the Desert Southwest.

The upper level ridge will continue to strengthen over the PacNW
through Friday, producing mostly light winds and warming
temperatures in the forecast area. Temperatures will be increasing
into the upper 80s and lower 90s by Friday, especially in the
Columbia Basin, Eastern Gorge, Yakima valley, and the John Day
Basin where the probability of exceeding 90 degrees is 70-90%.
These hot temperatures and the temperature differential between
here and west of the Cascades will also result in a cross Cascade
pressure gradient developing, leading to breezy winds through the
Cascade gaps in the late mornings and afternoons. Lastly,
deterministic and ensemble guidance has been consistent the past
several days in showing a weak plume of moisture in the mid-levels
across southern OR Friday into the weekend. This combined with
increasing instability at the surface will result in isolated
thunderstorms capable of gusty outflow winds developing mainly
across Grant county Friday afternoon. Lawhorn/82


.LONG TERM...Saturday through Wednesday...

Bottom Line Up Front (BLUF)

1. Thunderstorms along the OR Cascades and eastern mountains
Saturday through Sunday afternoon.

2. Abnormally high above climatological temperatures through the
long term.

Models are in firm agreement with there being an upper level ridge
in place over the PacNW with the leading edge of an upper level
trough pushing inland. The upper level flow will shift to
southwesterly across the region and models suggest a plume of
precipitation to accompany the leading edge. This upper level trough
will bring with it some instability over the region. Looking at a
forecast sounding over some of the the eastern mountains, there are
multiple ingredients leading to the development of thunderstorms.
Models sounding show MUCAPE values ranging from 800-1100 J/kg,
lifted index values of -2 to -5, lapse rates of 8-10 C/km with bulk
shear of 25-45 kts and PWATs nearing 0.9 inches. All these
ingredients together have lead the forecast to show thunderstorms.
However, looking at the ensembles, there is only a 20-30%
probability of thunder. If any storms do form, confidence is
moderate that these storms will produce damaging winds with intense
bouts of rain and hail. These ingredients do lessen through Sunday
with the ensembles showing a decrease to 15-20% probabilities of
thunder for much of Sunday.

EFI is showing temperatures across the entirety of the region to be
well above the climatological normal and only slightly moderating to
just above normal through the remainder of the period. Clusters show
the main variances to be with the amplitude of the ridge.
Regardless, temperatures will be on the warm side of things. Over
65% of the raw ensembles show the Pendleton area, foothills of the
Blues, Gorge and central OR to be in the upper 80s to low 90s
through the period. Over 45% of the raw ensembles show the Basin,
adjacent valleys to be in the low to mid 90s and the higher terrains
in the mid to upper 60s. Temperatures will remain similar through
the period with only a degree or two cool down as the trough makes
its way through. It will also depend on the path of the trough.
Clusters show variances in positioning and whether it will be an
open or closed system. Winds will be light and variable through the
period so they will provide little reprieve from the warm
temperatures.


&&

.AVIATION...Previous Discussion...18Z TAFs...VFR conditions will
persist through the forecast period. CIGs will remain mostly
FEW060 to start before giving away to SKC with winds generally
variable and under 10kts. Bennese/90


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  49  84  55  88 /   0   0   0   0
ALW  52  86  57  90 /   0   0   0   0
PSC  53  88  59  93 /   0   0   0   0
YKM  48  87  55  91 /   0   0   0   0
HRI  51  89  56  93 /   0   0   0   0
ELN  47  82  53  89 /   0   0   0   0
RDM  47  84  52  89 /   0   0   0   0
LGD  48  84  51  86 /   0   0   0   0
GCD  50  89  54  92 /   0  10   0  10
DLS  53  89  58  93 /   0   0   0   0

&&

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

$$

SHORT TERM...82
LONG TERM....90
AVIATION...90