760
FNUS75 KBOI 171853
FWSBOI

Spot Forecast for BIG GRASS...BLM
National Weather Service Boise ID
1253 PM MDT Thu Sep 17 2026

Forecast is based on forecast start time of 1800 MDT on September 17.
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.

...MOSTLY DRY AND WINDY THIS EVENING...
...SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS FRIDAY...
...WARMER AND DRIER SATURDAY WITH BREEZY NORTHWEST AFTERNOON WINDS...
...CONTINUED WARMING AND DRYING SUNDAY AND MONDAY WITH LIGHT WINDS...

.DISCUSSION...
Gusty southwest winds will persist through sunset today ahead of
an approaching cold front, while the area stays dry. Friday will
see a 20 percent chance of showers, and a 15% chance of thunderstorms
maximized late Friday afternoon. Breezy west winds Friday afternoon
following the frontal passage. High pressure rebuilding over the
area will return warmer temperatures Saturday, wuth dry conditions
and breezy northwest wind gusts up to 20 mph in the afternoon.
Continued drying and warming Sunday and Monday with only light west
or northwest winds in the afternoons.

.TONIGHT...

Sky/weather.........Mostly cloudy.
Min temperature.....45 to 51.
Max humidity........75 to 80 percent.
CWR.................0 percent.
Wind - 20 foot......West 10 to 15 mph. Gusts up to 25 mph in the
                    evening, becoming south 5 to 8 mph after sunset.
Mixing height.......200 ft AGL.
Transport winds.....Northwest around 5 mph.
Ventilation Index...10 poor.

.FRIDAY...

Sky/weather.........Mostly cloudy. A 20 percent chance of showers
                    and a 10 to 15 percent chance of thunder in the
afternoon.
Max temperature.....57 to 72.
Min humidity........35 to 50 percent.
CWR.................10 percent.
Wind - 20 foot......West-northwest 7 to 12 mph, with gusts up to 22
mph in the afternoon. Gusty and erratic outflows
up to 30 mph possible near thunderstorms in the
afternoon.
Mixing height.......7000 ft AGL.
Transport winds.....West around 10 mph.
Ventilation Index...700 excellent.

.FRIDAY NIGHT...

Sky/weather.........Mostly cloudy with a 10 to 15 percent chance of
                    showers/thunderstorms in the evening, then partly
cloudy overnight.
Min temperature.....43 to 50.
Max humidity........75 to 96 percent.
CWR.................0 percent.
Wind - 20 foot......West 6 to 12 mph, with gusts up to 22 mph in the
                    evening. South and diurnal 5 to 8 mph after sunset.
Mixing height.......200 ft AGL.
Transport winds.....Northwest around 5 mph.
Ventilation Index...10 poor.

.SATURDAY...

Sky/weather.........Mostly cloudy in the morning, becoming mostly sunny
                    in the afternoon.
Max temperature.....61 to 76.
Min humidity........23 to 33 percent.
CWR.................0 percent.
Wind - 20 foot......West 6 to 12 mph, with gusts up to 18 mph in the
                    afternoon.
Mixing height.......5500 ft AGL.
Transport winds.....Northwest around 10 mph.
Ventilation Index...550 good.

$$
Forecaster...Yang, Colin
Requested by...STEPHEN HAMMOND
Type of request...WILDFIRE
.TAG 2621735.6/BOI
.DELDT 09/17/26
.FormatterVersion 2.0.0
.EMAIL ROBERT_EGGERT@FIRENET.GOV,2026.biggrass.plans@firenet.gov,stephen_hammond@firenet.gov