483
FXUS66 KPDT 091752
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
952 AM PST Tue Dec 9 2025

.AVIATION...

An ongoing prolonged rain event will continue through this TAF
period. The east west axis of rains will shift from south to
north with time Today and Tonight, bringing a shift of mainly VFR
rains Today, to more lower cigs and to a lesser degree visibility
overnight as the boundary layer cools, especially in the higher
elevation + upslope prone terminals (YKM/ALW/PDT). Look for Cigs
in the 1-2kft in this locations as rains persist beyond the
sunset. As the night progresses, the rain will become more lacking
as the winds develop, mixing the surface layer enough to
reestablish VFR cigs and vsbys. Expect wind shear in the lowest
2000 ft (PDT/ALW/PSC) anywhere from 35 to 55kts after 09z.

&&

PREV DISCUSSION... /issued 329 AM PST Tue Dec 9 2025/

DISCUSSION...

Key Points:

1. Significant rainfall leading to flooding in some areas through
the week. *Flood Advisory and Warnings Active*

2. Breezy conditions through Thursday

3. Warm temperatures will continue through the long term

Current radar shows much of the incoming rainfall to be mostly on
the west side of the Cascades with some spill over in portions of
Kittitas and Yakima Counties as well as over the higher peaks of the
Blues. Winds are expected to begin settling through the morning with
ground observation showing gusts to be between 25-35 mph still.
Winds are expected to settle after 3-5 AM as the passage of the
front continues to move east.

Today through Thursday afternoon...Models show a relatively strong
atmospheric river has set up along the coast of WA and OR and
persisting through Thursday. This will bring widespread significant
rainfall to the region with QPF totals for today through Thursday
afternoon totaling to nearly 3 inches along the eastern slopes with
higher amounts along the crests. Models also show nearly 1-1.5
inches of precipitable water which is substantially higher than
the normal. CAMs raw ensembles (HREF) show the crests to the eastern
slopes through Ellensburg and the Dalles as well as the eastern
mountains through the Grande Ronde Valley and into Wallowa Valley
will see 0.05-1 inch or more of precipitation today (Tuesday)with 80-
90% confidence. This will continue through the day with ensembles
showing up to another inch of precipitation in the aforementioned
areas again Wednesday. However, backing off along the eastern
mountains and the Grande Ronde Valley where only 0.25-0.5 inches are
expected (60-80%). NBM raw ensembles show 25-65% chance of the lower
elevations such as the Basin and foothills of the Blues will see
0.25-0.30 inches in a 48 hour period and central OR will see 0.10
inches. With the significant rainfall across the WA Cascades, many
rivers are expected to reach/exceed bankfull through tomorrow.
Naches at Naches, Yakima at Horlick and Easton are all exceeding
action stage and into minor so a Flood Warning has been issued for
those locations. All other rivers in the area are still at or
nearing action stage and are continuing to be monitored as the event
continues to unfold.

Models show another cold front to make its way across the region
beginning Tuesday night and persisting through Wednesday bringing
another round of breezy conditions. Pressure gradients along the
Cascades with this front are not as strong as the previous with only
7-9 mb gradient. Winds will be from the southwest between 15-25 mph
sustained with gusts to 40 mph and will affect the wind prone Gap
areas as well as the eastern slopes, Horse Heaven Hills and the
Northern Blues of WA. After Wednesday, models show a more zonal flow
will rest over the region bringing winds back to a more diurnal
flow.

Lastly, models show that not only did this AR tap into an abundance
of moisture, but also in a abu-tropical flow that will bring with it
increasing temperatures. With the influx of warm air, temperatures
are expected to be 10-15 degrees warmer than seasonal average today
increasing to 15-25 degrees above seasonal average Wednesday. Short
term raw ensembles show elevations below 3500 feet will see
temperatures in the low to mid 50s Tuesday, with the exception of
Kittitas Valley where temperatures will be in the mid to upper 40s
(70-90% confidence). Moving to Wednesday, raw ensembles show the
same areas beginning to see temperatures in the low to mid 60s with
Kittitas Valley now seeing low to mid 50s (60-80% confidence).
Temperatures will steadily decrease as we move into the later
portion of the week, however, temperatures are expected to stay 10-
20 degrees above climatological normal. Essentially saying
temperatures will remain in the low to mid 50s. 90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  56  45  65  51 / 100  90  40  20
ALW  54  46  64  54 /  90  90  60  30
PSC  56  44  66  53 /  80  90  20  20
YKM  50  39  60  48 /  80 100  60  50
HRI  57  46  66  52 /  90  90  20  20
ELN  46  35  56  44 /  70 100  70  70
RDM  57  44  63  37 /  70  50  10   0
LGD  51  41  58  45 / 100 100  50  20
GCD  51  45  58  40 /  90  70  10  10
DLS  56  48  63  55 / 100 100  70  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Flood Watch through Friday morning for WAZ026-027-521>523.

&&

$$

SHORT TERM...99
LONG TERM....99
AVIATION...71