556
FXUS66 KPDT 291729
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1029 AM PDT Sun Jun 29 2025

.AVIATION...18Z TAFs...VFR conditions are very likely (>95%
chance) through the period for all sites. Clear skies and mostly
light (sustained at 10 kts or less), diurnally and terrain-driven
winds are forecast. Will note gust potential of 14-18 kts in the
afternoon and evening at BDN/RDM. Plunkett/86

&&

.PREV DISCUSSION... /issued 202 PM PDT Sat Jun 28 2025/

SHORT TERM...Today through Monday night...Quiet weather is
forecast for the remainder of today and Sunday as an upper-level
ridge of high pressure builds into the Pacific Northwest. Breezy
winds through the Cascade gaps this afternoon and evening will
diminish overnight with a reversal to a lighter offshore flow
anticipated Sunday into Monday.

Ensemble NWP is very confident (95% or greater) that the
aforementioned upper-level ridge will amplify through Monday, and
an upper-level closed low will develop off the central California
coast Sunday through Monday, setting the stage for area-wide heat
and convection in southern/eastern Oregon for Monday and Tuesday.
CAMs suggest the bulk of the convective activity Monday will be
across south-central Oregon with limited extension northward into
central Oregon due to weak forcing aloft. That said, have
introduced a slight chance (15%) of thunderstorms in the forecast
for the east slopes of the Oregon Cascades roughly from Santiam
Pass south, and across the Ochocos and John Day Highlands.

Anticipated warming under the upper-level ridge has prompted the
issuance of Heat Advisories for most of our lower-elevation areas
across northern Oregon and south-central Washington for Monday
through Tuesday. Widespread Moderate (level 2 of 4) to Major
(level 3 of 4) HeatRisk is on tap due to forecast high
temperatures of 90-103 degrees and overnight low temperatures of
59-73 degrees. Will note there is some uncertainty in high and low
temperatures Tuesday, (and especially Wednesday in the "LONG
TERM") due to potential cloud cover -- convective debris or
otherwise. Plunkett/86

LONG TERM...Tuesday through Friday...Confidence is high that an
upper-level ridge of high pressure will be overhead Tuesday.
Above-normal temperatures are expected region-wide, and mostly dry
conditions are anticipated outside of the Blue Mountains region
where a slight chance (15-24%) to chance (25-30%) of showers and
thunderstorms has been included due to the combination of
sufficient mid-level moisture, instability, and modest upper-
level forcing.

Wednesday through Friday, analysis of ensemble clusters indicates
there is more uncertainty (timing and amplitude of 500-hPa
heights) in pattern details, but guidance is strongly suggesting
one or more shortwaves embedded within broadly southwesterly flow
aloft. This pattern favors showers and thunderstorms for the Blue
Mountains region, so have added a slight chance (15%) of thunder
each afternoon.

Otherwise, breezy to windy westerly winds are favored through the
Cascade gaps Wednesday through Friday. Confidence in surface
moisture (dew point and relative humidity) is still low (<30%)
due to aforementioned uncertainty in pattern details so will hold
off on mentioning potential for any fire weather highlights.
Plunkett/86

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  92  60  99  66 /   0   0   0   0
ALW  90  64  96  69 /   0   0   0   0
PSC  93  59 100  63 /   0   0   0   0
YKM  90  61  98  66 /   0   0   0   0
HRI  93  59 100  65 /   0   0   0   0
ELN  91  59  98  66 /   0   0   0   0
RDM  90  51  96  58 /   0   0   0  10
LGD  87  56  94  62 /   0   0   0   0
GCD  90  56  97  61 /   0   0   0  10
DLS  94  64 100  68 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory from 9 AM Monday to 9 PM PDT Tuesday for ORZ041-
     044-507-508-510.

WA...Heat Advisory from 9 AM Monday to 9 PM PDT Tuesday for WAZ024-
     026>029-521.

&&

$$

SHORT TERM...86
LONG TERM....86
AVIATION...86