Flash Flood Warning 2, NWS Riverton, WY

454 
WGUS75 KRIW 170032
FFSRIW

Flash Flood Statement
National Weather Service Riverton WY
632 PM MDT Thu Jul 16 2026

WYC003-043-170130-
/O.CON.KRIW.FF.W.0002.000000T0000Z-260717T0130Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Big Horn WY-Washakie WY-
632 PM MDT Thu Jul 16 2026

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 730 PM MDT THIS
EVENING FOR SOUTH CENTRAL BIG HORN AND NORTHERN WASHAKIE COUNTIES...

At 632 PM MDT, Doppler radar indicated thunderstorms which produced
heavy rain across the warned area. Between 1.5 and 2.5 inches of rain
fell earlier this afternoon on the normally dry washes and gulches
that feed into the Nowood River upstream of Manderson. Flash flooding
may be occurring in the warned area.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Radar indicated.

IMPACT...Flash flooding of small creeks and streams, as well as other
         poor drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Mainly rural areas of South Central Big Horn and Northern Washakie
  Counties along the Nowood River upstream of Manderson.

This includes the following streams and drainages...
  Betonite Ridge Draw, Paint Rock Creek, South Fork Brokenback Creek,
  Hidden Dome Draw, Nowood River, Sand Creek, Zeisman Dome Draw, East
  Fork McDermotts Gulch, Buffalo Creek, Weintz Draw, Brokenback Creek
  and Big Cottonwood Creek.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.

Be aware of your surroundings and do not drive on flooded roads.

In hilly terrain there are hundreds of low spots and normally dry
water crossings which are potentially dangerous in heavy rain. Do not
attempt to cross flooded roads. Find an alternate route.

&&

LAT...LON 4417 10783 4425 10792 4429 10792 4425 10774
      4414 10750 4406 10744 4404 10757 4406 10774
      4414 10780

FLASH FLOOD...RADAR INDICATED

$$

VandenBoogart

131 
WGUS75 KRIW 170131
FFSRIW

Flash Flood Statement
National Weather Service Riverton WY
731 PM MDT Thu Jul 16 2026

WYC003-043-170141-
/O.EXP.KRIW.FF.W.0002.000000T0000Z-260717T0130Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Big Horn WY-Washakie WY-
731 PM MDT Thu Jul 16 2026

...FLASH FLOOD WARNING HAS EXPIRED FOR SOUTH CENTRAL BIG HORN AND
NORTHERN WASHAKIE COUNTIES...

The heavy rain has ended in the previously warned area. Although
flooding is no longer expected to pose a immediate threat, storms
with heavy rainfall potential will continue in the region through the
late evening hours. Please continue to heed any road closures.

A Flood Watch remains in effect until 1100 PM MDT for portions of
central and western Wyoming.

&&

LAT...LON 4417 10783 4425 10792 4429 10792 4425 10774
      4414 10750 4406 10744 4404 10757 4406 10774
      4414 10780

$$

VandenBoogart

Area Forecast Discussion
National Weather Service Riverton WY
1233 PM MDT Thu Jul 16 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected through at
  least sunset across western and northern Wyoming. Heavy
  rainfall with localized flash flooding is possible in any
  thunderstorm, especially for west and southwest portions of
  the Bighorn Basin.

- More shower and thunderstorm chances across western and
  northern through Saturday. The thunderstorm threat becomes
  more widespread across the state Sunday through the middle of
  next week, with a continued threat for flash flooding.

- Hot temperatures are expected through Sunday with highs in the
  upper 80s to upper 90s. Some locations across the Bighorn
  Basin and Johnson and Natrona Counties could reach 100 degrees
  Friday through Sunday.

&&

.UPDATE...
Issued at 1230 PM MDT Thu Jul 16 2026

As mentioned in the morning discussion, today will be a lot like
yesterday with scattered showers and thunderstorms. However, unlike
Wednesday/yesterday, most of the area has been sunny this morning.
This morning sunshine has allowed the atmosphere to destabilize.
This means that locations such as western Wyoming are expected to
see more thunderstorm activity compared to the showery activity from
yesterday. There is plenty of available moisture in the atmosphere,
with the 18Z sounding from Riverton showing precipitable water
amounts of 1.06", which is around 180% of normal. These high
precipitable water amounts combined with slow storm motions of 10 to
15 kts will keep heavy rainfall with localized flash flooding as the
primary thunderstorm threat today. The areas of greatest concern are
the Absarokas, Cody Foothills, and Hot Springs County. These areas
are particularly susceptible due to favorable easterly surface flow,
thanks to a surface low over southern Wyoming, and 0.5" to 2.5" of
rain in these areas Wednesday afternoon. Thus, the Flash Flood Watch
remains in effect through midnight tonight for the aforementioned
locations. Areas outside of the Flash Flood Watch still have the
potential for heavy rainfall with localized flash flooding, so it is
important to remain weather aware. A secondary threat from
thunderstorms will be gusty 35 to 50 mph winds and small hail, with
isolated gusts up to 60 mph not out of question due to DCAPE values
around 1,200 J/kg. The threat for thunderstorms is greatest through
sunset with the overall coverage decreasing through 3AM. Showers and
thunderstorm chances exist across most of western and northern
Wyoming, with Natrona County and eastern Fremont and Sweetwater
Counties likely (90% or greater) remaining dry today.

&&

.DISCUSSION...
Issued at 203 AM MDT Thu Jul 16 2026

It is amazing how quickly things can change with the weather in
Wyoming. Just a couple days ago we were talking about record heat
and very dry conditions. Well, the weather has decided to do a
Freaky Friday on us and flip into full monsoon mode. We had some
reports of flooding today and the chance will be around through the
next several days.

Water vapor imagery shows a large plume of monsoonal moisture
continuing to stream northward from the Gulf of California and up
through the Great Basin and into the northern Rockies. We continue to
have some rain and some thunderstorms early this morning, especially
in the south which just happened to light up when the previous shift
left for the night. Luckily, the storms have some movement but there
have been some good local rains, Big Piney got a quarter of an inch
in only 20 minutes. The general trend is down through tonight
and most places should be rain free by sunrise. However, things
look similar to yesterday, with low level easterly upslope flow
and abnormally high precipitable water levels, as high as 200
percent of normal. There is some steering flow but again, not a
lot. So, it looks almost like a repeat performance of yesterday
with slow moving showers and thunderstorms, although it could be
a bit further east that yesterday. Instability parameters are
decent as well with up to 1000 J/Kg of CAPE and lifted indices
as low as minus 4. There is not a lot of upper level forcing
though so most storms should largely be rain makers although you
can't rule out small hail or a strong wind gust with any storm
in Wyoming. With the local flooding we had yesterday and a
similar setup to Wednesday, we have decided to issue a flood
watch through midnight for the Absarokas, Cody Foothills as well
as Hot Springs County given the favored low level easterly flow
bringing upslope flow and slow movement of the storms. Like
yesterday, the most numerous storms should end after sunset, but
a few will linger after midnight. Temperatures should be a few
degrees cooler than yesterday, but still above normal for this
time of year.

I still feel there may be a bit less coverage on Friday and
Saturday, especially in central Wyoming. It still looks like
ridge may build a back to the west somewhat on these days. This
should decrease available moisture and instability somewhat,
especially in eastern portions of the area. However, it will be
going back to 150 to 175 percent of normal versus 200 percent,
so not a huge difference. The POPs reflect this fairly well
again, with the highest in the western mountains on each day.
And like the previous days, most should be diurnal but a few
showers could linger after midnight and possibly until sunrise
the next day. Temperatures will also warm a bit, especially East
of the Divide, with some of the warmer spots getting close to
the 100 degree mark once again.

Sunday still looks like the transition day when the monsoonal push
will begin to move eastward, bring a better chance of showers and
storms to areas East of the Divide and fewer storms across western
Wyoming. Precipitable waters remain high all the way through much of
next week as well, as high as 200 percent of climatological normals.
There are still differences in the guidance in regards to which day
will be the most active though, as is to be expected this far out.
However, all areas should have a decent chance of getting some
needed rain over the next several days. We just don't want too much
at once. And unfortunately, that is a definite possibility as well.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1053 AM MDT Thu Jul 16 2026

TCU have begun to form atop local mountain ranges currently,
with continued development into SHRA/TSRA this afternoon. Any
storms that do form will be slow-moving, with locally heavy
rainfall. Main focus will be central and northern WY sites this
afternoon during peak heating, shifting into KRKS early evening.
No precip expected at KCPR again this afternoon. Activity will
be slow to decrease in the evening, as daytime heating is strong
today, and heat will be slow to release. Expect mostly clear
skies and lighter winds tonight. Another round of peak heating
thunderstorms returns on Saturday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Flood Watch until midnight MDT tonight for WYZ002-003-005-007.

&&

UPDATE...Gerhardt
DISCUSSION...Hattings
AVIATION...Straub