516
FXUS66 KPDT 021802
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1102 AM PDT Tue Sep 2 2025

.UPDATED AVIATION.

.AVIATION...18Z TAFs...VFR conditions prevail with winds light and
variable. Occasional gust of wind up to 15 knots for the DLS
tomorrow afternoon. VCSH for BDN/RDM tomorrow morning as areas of
showers develop close to central OR. No VIS or CIG issues
expected.



&&

.PREV DISCUSSION... /issued 1020 PM PDT Mon Sep 1 2025/

AVIATION...06Z TAFs...VFR conditions to prevail through the
period. Isolated thunderstorms are expected to develop across
portions of south central and central OR tomorrow, with hi-res
guidance indicating storms moving up the east slopes of the OR
Cascades and to the west of sites RDM/BDN. Have left out mention
of any thunderstorm chances at these sites at this time. Winds
will be 12kts or less and diurnally/terrain driven through the
period. Lawhorn/82

PREV DISCUSSION... /issued 136 PM PDT Mon Sep 1 2025/

DISCUSSION...
The region has been between two systems today, a large area of
high pressure to the east and an area of low pressure off the
coast. As we progress over the next couple of days, the strong
high pressure will move over the westward, closer to the Pacific
Nortwest. As a result, the low off the coast will also be pushed
west.

The main weather story through midweek will be unseasonably hot
temperatures. With the start of September, high normal high
temperatures across most lower elevation areas are around 80
degrees, with several locations a bit lower, and some locations a
couple of degrees higher. Through Thursday, temperatures will be
10 to as much as 20 degrees above normal. High temperatures will
range from the mid 90s to around 100 degrees in the Columbia
Basin,, Yakima Valley, Kittitas Valley, Columbia Gorge and
Foothills of the Blue Mountains. ECMWF EFI values are 1.00 across
the Columbia Basin, Tuesday and especially Wednesday and Thursday,
owing to the lower seasonal normals in September. Several daily
records will be challenged.

HeatRisk Values will rise to Major in most of these areas, with a
large area of Moderate surrounding them. Extreme Heat Warnings
have been issued for the Basin, Gorge, Foothills of the Northern
Blue Mountains and Yakima and Kittitas Valleys for Tuesday through
Thursday. Heat Advisories have been issued for central Oregon,
portions of the Blue Mountains and the John Day Basin for
Tuesday. These may need to be extended further into Wednesday.

Smoke and cloud cover can prevent any area from reaching forecast
high temperatures, especially given the shorter days in early
September.

Temperatures decrease by 4 to 5 degrees Friday, but remain above
normal, and further decrease Saturday and Sunday. By Sunday, high
temperatures may be approaching seasonal normals.

A short wave will move into southern Oregon from the south on
Tuesday will trigger some showers or thunderstorms, mainly in
central Oregon. Guidance has been keeping most of the activity to
our south and west, but coan`t rule out a shower or thunderstorm
across this area later Tuesday afternoon into Tuesday evening.
Another chance of showers and isolated thunderstorms develops on
Wednesday and through the end of the week. Again, guidance
disagrees on exactly where any activity will develop, but central
Oregon seems to be an area of focus. Wednesday is outside of the
time range of the CAMS models so hopefully we will get some better
agreement as new runs come in.

Beyond Wednesday there is general disagreement, as the ridge
begins to break down and an upper trough moves begins to impact
the area. There will likely be some showers/thunderstorms by the
weekend, along with cooler temperatures by Saturday but the
timing remains in question. The GFS has a better chance of
precipitation on Thursday, while the ECMWF has virtually none.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  66  98  67  97 /   0   0   0   0
ALW  70 100  72  98 /  10   0   0   0
PSC  62 101  64  99 /   0   0   0   0
YKM  65 101  67 100 /   0   0   0   0
HRI  63 100  66  99 /   0   0   0   0
ELN  62 100  64  97 /   0   0   0   0
RDM  59  93  54  94 /  20  10  10  10
LGD  62  98  62  97 /   0   0   0   0
GCD  62  96  62  95 /  10   0   0   0
DLS  69 101  68 100 /  10   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Extreme Heat Warning until 8 PM PDT Thursday for ORZ041-044-507-
     508-510.

     Heat Advisory until 8 PM PDT this evening for ORZ049-502-505-511.

WA...Extreme Heat Warning until 8 PM PDT Thursday for WAZ024-026>029-
     521.

     Heat Advisory until 8 PM PDT this evening for WAZ030-523.

&&

$$

SHORT TERM...77
LONG TERM....77
AVIATION...95