712
FNUS75 KBOI 151818
FWSBOI

Spot Forecast for BIG GRASS...BLM
National Weather Service Boise ID
1218 PM MDT Tue Sep 15 2026

Forecast is based on forecast start time of 1800 MDT on September 15.
If conditions become unrepresentative...contact the National Weather
Service.

Please contact our office at (208)334-9060, if you have questions
or concerns with this forecast.

...WARMING TREND THRU WEDNESDAY...
...SHOWERS AND THUNDERSTORMS POSSIBLE THURSDAY...

.DISCUSSION...
Colder temperatures again tonight will allow good RH recovery,
supporting a chance for frost in the area. Temperatures remain
around normal into the weekend. Upper low approaching the region
late Wednesday bringing a chance (30%) of showers and
thunderstorms through late Thursday night. Winds increases from
the east ahead of the system Wednesday than switching to the
southwest ahead of the front on Thursday than switching to the
west on Friday following the frontal passage.

.TONIGHT...

Sky/weather.........Mostly cloudy.
Min temperature.....43 to 53.
Max humidity........46 to 56 percent.
CWR.................0 percent.
Wind - 20 foot......Northeast 9 to 15 mph with gusts to around 22
                    mph.
Mixing height.......100 ft AGL.
Transport winds.....East around 10 mph.
Ventilation Index...10 poor.

.WEDNESDAY...

Sky/weather.........Sunny.
Max temperature.....73 to 83.
Min humidity........14 to 24 percent.
CWR.................0 percent.
Wind - 20 foot......East 7 to 13 mph with gusts to around 20 mph.
Mixing height.......8000 ft AGL.
Transport winds.....Southeast around 10 mph.
Ventilation Index...800 excellent.

.WEDNESDAY NIGHT...

Sky/weather.........Partly cloudy.
Min temperature.....50 to 55.
Max humidity........58 to 68 percent.
CWR.................10 percent.
Wind - 20 foot......Southeast 8 to 14 mph. Gusts up to 18 mph in
                    the evening increasing to 24 mph overnight.
Mixing height.......200 ft AGL.
Transport winds.....East around 10 mph.
Ventilation Index...20 poor.

.THURSDAY...

Sky/weather.........Mostly sunny.
Max temperature.....68 to 78.
Min humidity........19 to 29 percent.
CWR.................0 percent.
Wind - 20 foot......South 12 to 18 mph with gusts to around 28 mph.
Mixing height.......9500 ft AGL.
Transport winds.....Southwest around 15 mph.
Ventilation Index...1425 excellent.

$$
Forecaster...Smith
Requested by...STEPHEN HAMMOND
Type of request...WILDFIRE
.TAG 2621735.4/BOI
.DELDT 09/15/26
.FormatterVersion 2.0.0
.EMAIL ROBERT_EGGERT@FIRENET.GOV,2026.biggrass.plans@firenet.gov,stephen_hammond@firenet.gov