783
FNUS76 KOTX 181959
FWSOTX

Spot Forecast for Upper Smith...USFS
National Weather Service Spokane WA
1259 PM PDT Tue Aug 18 2026

Forecast is based on forecast start time of 0600 PDT on August 19.
.DISCUSSION...

209:
On Tuesday, warm and relatively moist conditions were observed
over the fire with high temperatures in the 70s and 80s and minimum
relative humidity values in the upper 20 percent range. Good to
Excellent overnight humidity recovery occurred Tuesday morning.
Daytime heating along with a weak weather disturbance to the north
resulted in afternoon cumulus cloud development. Winds were
generally light with southwest gusts up to 15 on the ridgelines
and variable winds in the drainages.

The airmass will remain mild with a subtle drying and warming
trend through Friday. Winds will be light and mainly terrain
driven in the drainages with south to southwest ridgeline gusts up
to 15 mph on Wednesday. There is a 20-30% chance for showers and
thunderstorms near the fire late Friday night into Saturday. Any
storms over or near the fire will bring a threat for gusty outflow
winds and isolated rainfall ranging from a trace to a quarter of
an inch.

Spot Discussion:
Expect a subtle warming and drying trend the next several days
with highs warming into the into the 80s and relative humidity
values in the low 20s by Thursday. Winds will be primarily terrain
driven in the valleys with west to southwest gusts up to 15 mph
on the ridgelines on Wednesday. Winds will trend lighter for
Thursday, but instability increases with mixing heights peaking
around 8000 ft AGL in the afternoon.

If conditions become unrepresentative, contact the National Weather
Service.
***************************************************************
Forecasts for 20 foot wind speeds (valleys and ridge tops) are
10 minute averages reflecting RAWS wind.
***Ventilation Index is derived from transport wind
   multiplied by the mixing height divided by 100.
   Categories: low (< 200), moderate (200-500),
   high (500-800), and very high (> 800).
***************************************************************

.WEDNESDAY...

Sky/weather.........Sunny.
CWR.................0 percent.
Chance of lightning.0 percent.
Max temperature.....Around 78.
Min humidity........25-30 percent.
Wind (20 ft)........Upslope/upvalley 2 to 5 mph in the valleys.
                    West to southwest 5 to 8 mph on ridgelines.
Mixing height.......7000 ft AGL in the afternoon.
Transport winds.....Light winds becoming southwest around 9 mph in
                    the afternoon.
Ventilation Index...Moderate (212) increasing to high (635) in the
                    afternoon.

.WEDNESDAY NIGHT...

Sky/weather.........Partly cloudy.
CWR.................0 percent.
Chance of lightning.0 percent.
Min temperature.....Around 57.
Max humidity........49 percent.
Wind (20 ft)........Downslope/downvalley 1 to 4 mph.
Mixing height.......4500 ft AGL falling to near the surface.
Transport winds.....Southwest 5 to 7 mph.
Ventilation Index...Moderate (332) decreasing to low (24)
                    overnight.

.THURSDAY...

Sky/weather.........Sunny.
CWR.................0 percent.
Chance of lightning.0 percent.
Max temperature.....Around 81.
Min humidity........20-25 percent.
Wind (20 ft)........Upslope/upvalley 2 to 4 mph.
Mixing height.......8000 ft AGL in the afternoon.
Transport winds.....Light winds becoming southwest around 9 mph in
                    the afternoon.
Ventilation Index...Low (139) increasing to high (733) in the
                    afternoon.

$$
Forecaster...VT
Requested by...David Pearson
Type of request...WILDFIRE
.TAG 2619090.13/OTX
.DELDT 08/18/26
.FormatterVersion 2.0.0
.EMAIL david_pearson@firenet.gov,IDCDC@firenet.gov,2026.uppersmith.plans@firenet.gov