747
FXUS66 KPDT 082336
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
436 PM PDT Fri Aug 8 2025

.DISCUSSION...Northwest flow will continue over the region through
early Saturday. Then, a strong high pressure system will begin to
move eastward from the Pacific Ocean later Saturday into Sunday.
This high will remain over the area Monday into Tuesday before being
suppressed southward.

High temperatures will increase into the weekend and early next
week, with Monday likely being the hottest day, with upper 90s to
triple digits in the Columbia Basin and surrounding areas.
HeatRisk values will be widespread moderate and major HeatRisk in
the lower valleys. These temperatures will be 10 to 15 degrees
above normal.

However, before we get to the hot temperatures, another relatively
cool night is in store tonight with many locations in the 40s and
50s.

Sunday looks to have high temperatures in the mid to upper 90s
with areas of moderate HeatRisk.

There is still some uncertainty as to Tuesday`s highs but
temperatures have trended upward with today`s model runs, and
temperatures look similar to Monday at this point.

Based on all of this information, have opted to issue an Extreme
Heat Watch for Sunday through Tuesday. Will see how later guidance
trends for later headlines, and it is possible some of the watches
end up as advisories and others as warnings.

NBM probabilities of high temperatures >= 100 degrees range from
20 to 50 percent on Sunday, mainly across portions of the Basin
and central Oregon, and jump to 60 to over 90 percent Monday and
Tuesday. The GFS has about 50 percent of its ensemble members
>=100 degrees on Sunday for the Columbia Basin, while in the
ECMWF, its about 80 percent.

The ECMWF EFI brings 0.7 to 0.8 anomalies for high (and low)
temperatures especially across the Basin by Monday and Tuesday,
with a large area of 0.6 to 0.7 surrounding it.

High temperatures will begin to cool on Wednesday as a weak trough,
moves into the Pacific Northwest, followed by zonal flow. High
Thursday will be even cooler than Wednesday, and will end up close
to normal by the end of the week.

No precipitation is forecast through the week. With humidities
staying low around or below 20 percent through Wednesday in many
ares, any increase in winds with the trough moving onshore will
bring enhanced fire weather concerns and this is something we will
have to watch especially in the later Tuesday into Wednesday time
frame. Beyond Wednesday, the cooler temperatures will bring
increased humidity, which should help alleviate any fire weather
concerns.

&&

.AVIATION...00Z TAFs...VFR conditions are forecast through
the valid period for all sites. Aside from some high cloud, skies
will be mostly clear. Diurnally driven winds of 10 kts or less are
forecast, except at DLS, which will see some gusts to around 20 kts
late this afternoon and evening before returning to 10 kts or less
overnight. Plunkett/86

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  56  89  59  94 /   0   0   0   0
ALW  61  89  64  94 /   0   0   0   0
PSC  57  91  60  97 /   0   0   0   0
YKM  59  91  62  96 /   0   0   0   0
HRI  58  91  60  97 /   0   0   0   0
ELN  59  87  61  96 /   0   0   0   0
RDM  46  88  51  94 /   0   0   0   0
LGD  52  86  55  91 /   0   0   0   0
GCD  51  86  54  92 /   0   0   0   0
DLS  62  90  66  99 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Extreme Heat Watch from Sunday afternoon through Tuesday evening
     for ORZ041-044-505-507-508-510-511.

WA...Extreme Heat Watch from Sunday afternoon through Tuesday evening
     for WAZ024-026>029-521.

&&

$$

SHORT TERM...77
LONG TERM....77
AVIATION...86