717
FNUS75 KRIW 211038
FWSRIW

Spot Forecast for Butterfly Fire...Casper Interagency Dispatch Center
National Weather Service Riverton WY
438 AM MDT Tue Jul 21 2026

Forecast is based on forecast start time of 0600 MDT on July 21.
If conditions become unrepresentative, contact the National Weather
Service

.DISCUSSION...

Monsoonal moisture will continue to flow over the fire site and bring
continuing chances of showers and thunderstorms. A shower or storm
can`t be ruled out in the morning hours, but the chance is only
around 10 percent. The chance of showers and thunderstorms begins to
increase after 1200, with the best chance between 1700 and 2100, when
the best chance of a wetting rain. Wind should remain on the light
side and largely terrain driven except in and around showers and
thunderstorms. Most showers and storms will end by midnight, although
there is around a 10 percent chance of one lingering through the night.
Mixing and smoke dispersal should become good to very good after 1200.
The chance of showers and thunderstorms peaks on Wednesday, with
gradually diminishing chances on Thursday and especially Friday and
Saturday.

...Thunderstorms imply strong gusty and erratic winds...

.TODAY...

Sky/weather.........Partly sunny (30-40 percent). Chance of
                    showers and thunderstorms in the afternoon,
                    mainly after 1600.
CWR.................20 percent.
Chance of pcpn......40 percent.
Chance of thunder...35 percent.
Max temperature.....Around 92.
Min humidity........19 percent.
Wind (20 ft)........Light winds. Gusty and erratic winds expected
                    near thunderstorms.
Ridgetop wind.......North around 10 mph until 0800, then light
                    until 1300, then west around 10 mph.
Mixing height.......2000 ft AGL until 1100, rising to 9000 feet by
                    1300.
Transport winds.....Northeast 7 to 9 mph until 0900, then southwest
                    6 to 12 mph
Smoke dispersal.....Poor until 1100, becoming good by 1300

TIME (MDT)      6AM 7AM 8AM 9AM 10A 11A 12P 1PM 2PM 3PM 4PM 5PM
Sky (%).........50  40  35  30  25  25  35  30  25  20  30  40
Weather cov.....                        SCH SCH SCH SCH CHC CHC
Weather type....                        RW  RW  RW  RW  RW  RW
Tstm cov........                        SCH SCH SCH SCH CHC CHC
CWR.............0   0   0   0   0   0   0   0   0   0   0   0
Chc of pcpn (%).10  10  10  10  10  10  10  10  20  20  30  40
Chc of thdr (%).0   0   0   0   0   0   10  10  20  20  30  40
Temp............68  69  71  73  77  81  86  88  90  92  89  86
RH..............54  57  48  45  41  36  31  26  21  19  20  23
20 FT wind dir..NW  N   NE  NE  E   S   SW  SW  W   W   W   NW
20 FT wind spd..4   3   2   2   2   2   2   3   4   5   6   6
20 FT wind gust.6   6   6   6   6   6   6   6   7   8   10  11
Ridge wind dir..NW  N   NE  NE  E   SW  SW  SW  W   W   W   NW
Ridge wind spd..10  10  5   5   5   5   5   10  10  10  10  10
Mix hgt (kft)...0.5 0.5 0.5 1.5 2.0 3.5 6.0 9.0 11  12  12  7.5
Transp wind dir.NE  NE  E   SE  S   S   S   S   SW  SW  SW  SW
Transp wind spd.9   8   7   7   7   7   8   8   9   10  12  12
SDspl kt-ft/10004   4   4   9   13  20  41  64  87  106 114 76

.TONIGHT...

Sky/weather.........Mostly cloudy (70-80 percent). Showers likely and
                    chance until 2100, then slight chance of showers.
CWR.................33 percent decreasing to 1 percent overnight.
Chance of pcpn......70 percent.
Chance of thunder...32 percent.
Min temperature.....Around 59.
Max humidity........78 percent.
Wind (20 ft)........Northeast around 8 mph until 2100, then east
                    until 2400, then light. Gusty and erratic winds
                    expected near thunderstorms.
Ridgetop wind.......Northeast around 15 mph until 2100, then
                    southwest 8 to 12 mph after 0100.
Mixing height.......4000 ft AGL until 1900, then 500 ft AGL.
Transport winds.....East to northeast 13 to 16 mph until 2400, then
                    east around 14 mph until 2300, then south to
                    southwest 9 to 13 mph..
Smoke dispersal.....Fair until 1900. Poor after 2100.

TIME (MDT)      6PM 7PM 8PM 9PM 10P 11P MID 1AM 2AM 3AM 4AM 5AM
Sky (%).........50  80  90  90  80  90  80  85  75  60  80  80
Weather cov.....CHC LKY LKY CHC CHC CHC SCH SCH
Weather type....RW  RW  RW  RW  RW  RW  RW  RW
Tstm cov........CHC CHC CHC SCH SCH SCH
CWR.............30  30  30  30  30  30  0   0   0   0   0   0
Chc of pcpn (%).40  60  70  40  40  40  20  20  10  10  10  10
Chc of thdr (%).30  30  30  20  20  20  10  10  10  0   0   0
Temp............84  86  81  76  74  71  69  68  66  64  63  62
RH..............27  30  33  46  51  54  57  60  64  72  73  72
20 FT wind dir..NE  NE  NE  E   E   E   E   S   SW  SW  SW  SW
20 FT wind spd..6   8   8   7   7   7   6   6   6   5   5   4
20 FT wind gust.13  11  11  10  10  8   7   7       6   6   6
Ridge wind dir..NE  NE  NE  NE  NE  NE  NE  S   SW  SW  SW  SW
Ridge wind spd..15  15  15  15  15  15  10  10  10  10  10  10
Mix hgt (kft)...4.0 2.0 1.5 1.0 1.0 1.0 1.0 0.5 1.0 1.0 0.5 0.5
Transp wind dir.NE  NE  E   E   E   E   E   S   S   W   W   W
Transp wind spd.13  16  15  14  14  14  12  13  12  10  10  9
SDspl kt-ft/100047  27  17  10  12  11  9   7   9   7   5   4

.FORECAST DAYS 3 THROUGH 5...
.THURSDAY...
Mostly cloudy. Showers and chance of thunderstorms. Lows in the
upper 50s. Highs in the lower 80s. Southwest winds around 7 mph.
.FRIDAY...
Partly cloudy. Chance of showers and thunderstorms. Lows in the
upper 50s. Highs in the mid 80s. Light winds.
.SATURDAY...
Mostly clear. Lows around 60. Highs in the upper 80s. Light
winds.

$$
Forecaster...Hattings
Requested by...Teddy Donoghue
Type of request...WILDFIRE
.TAG 2617850.0/RIW
.DELDT 07/21/26
.FormatterVersion 2.0.0
.EMAIL jfensel@blm.gov,wycpc@firenet.gov