489
FXUS66 KPDT 160536
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1036 PM PDT Fri Aug 15 2025

.Update for Aviation...

.AVIATION...
06Z TAFS...VFR conditions are expected, for the most part,
through the period. However, there could be MVFR VSBYS (40-60%)
and even CIGS Saturday during the late morning and early afternoon
as a cold front moves through and brings RA across the region.
The most likely locations to see MVFR are BDN and RDM but if the
rain is heavy enough they could occur just about anywhere. There
is also a slight chance (20%)of TSRA Saturday afternoon/evening.
Most of the activity should remain south and east of the TAF
sites. Once again, BDN and RDM look to have the best shout of the
small potential, but sine the probabilities are low, will not
include in the forecasts at this time.

Rain should end from west to east and all sites should see
decreasing clouds by late afternoon, early evening.

Outside of any thunderstorms or a gusty shower, winds will
generally be 10 kts or less, except at DLS, where once again
gusts to 25 kts are expected in the afternoon and evening hours.

&&

.PREV DISCUSSION... /issued 403 PM PDT Fri Aug 15 2025/

AVIATION...00z TAFs...A frontal system will pass through the
forecast area late tonight through early tomorrow morning,
bringing a round of rain showers to all TAF sites. MVFR conditions
are possible (40-50%) under showers, which are mainly expected to
last between 12z and 20z for most sites, except for YKM and DLS,
where spotty shower activity may occur earlier. Clearing will then
take place by early Saturday afternoon, with winds generally SW
to W. Evans/74

PREV DISCUSSION... /issued 220 PM PDT Fri Aug 15 2025/

DISCUSSION...Today through Thursday night...

Key Messages:

1. Flash Flood Watch over burn scars Saturday.

2. Afternoon and evening thunderstorms Saturday and Sunday.

3. Warming and drying through next week.

Current radar and visible satellite imagery shows light returns
over the Washington Cascades and east slopes as the area is under
partly to mostly cloudy skies. These conditions are a result of
the incoming cold front that is associated with an upper level
trough positioned off the coast of British Columbia that will
stay parked at this location into next week. A cold front is
poised to pass over the area tonight into Saturday, bringing
widespread rainfall to the region with isolated afternoon
thunderstorms along the Blue Mountain foothills and east both
Saturday and Sunday. The main concerns will include frequent
lightning, gusty winds, and periods of heavy rainfall. Both the
GFS and ECMWF suggest Precipitable Water amounts of around 1.5",
which is 200-250% above normal. This amount of moisture may lead
to rain rates of up to 1 inch an hour, which may pose a threat of
flash flooding or debris flows in areas near burn scars. The burn
scars of concern are those associated with fire seasons 2024 and
2025 as the lack of vegetation has weakened the overall structure
of the terrain. The NBM and HREF advertise CAPE values of 150-350
J/kg across Central, North-Central, and Eastern Oregon, which does
suggest a 20-30% chance of isolated thunderstorm developing both
Saturday and Sunday. This has also warranted the Storm Prediction
Center to include these areas in the General Thunderstorm (0 of 5)
category in their Convective Outlook product. Fire start concerns
associated with any developing thunderstorms is minimal, as the
NBM highlights a 70-90% chance of a wetting rain to occur
associated with the passing cold front.

Rain and thunderstorm chances taper off Sunday night into Monday
morning as an upper level ridge begins to build over the Four
Corners area and infiltrate into the Pacific Northwest.
Temperatures should rebound back to normal values on Monday and
begin on their upward trend through the remainder of the week,
eventually reaching into the mid-to upper 90s on Friday. This
warmer airmass will also lead to afternoon humidities dropping
back into the upper teens across portions of Central Oregon on
Monday. By Thursday, afternoon humidities across the area will
hover in the upper teens to low 20s as moderate (50-65%) overnight
humidity recoveries Thursday morning transition to poor (30-50%)
Friday morning. At this time, winds do look to stay relatively
light through the week, but some long-term guidance hints at a
shortwave riding through the Pacific Northwest to erode the upper
level ridge. Timing and strength of this shortwave does lack
consistency within ensembles and subsequent runs, so confidence in
the impacts to fire weather is quite low - but something to be
monitored. 75

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  62  79  59  83 /  20  70  10  10
ALW  65  79  62  84 /  20  70  10   0
PSC  65  85  58  86 /  30  70   0   0
YKM  65  85  55  83 /  80  60   0   0
HRI  64  84  60  86 /  30  70  10   0
ELN  60  80  53  79 /  80  50   0   0
RDM  55  77  49  83 /  40  80  10  10
LGD  59  79  55  83 /  10  50  40  20
GCD  58  79  55  83 /  10  40  30  30
DLS  67  82  60  82 /  80  70   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Flash Flood Watch from Saturday morning through Saturday evening
     for ORZ503-505-506.

WA...None.
&&

$$

SHORT TERM...75
LONG TERM....75
AVIATION...77