An upper-level disturbance moving through west-northwest flow aloft combined with daytime heating to generate two rounds of thunderstorms across central and northern Wyoming. The first round produced fast-moving thunderstorms that brought forth strong outflow wind in western Natrona County.
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The episode as NWS RIW wrote it up.
An upper-level disturbance moving through west-northwest flow aloft combined with daytime heating to generate two rounds of thunderstorms across central and northern Wyoming. The first round produced fast-moving thunderstorms that brought forth strong outflow wind in western Natrona County. The second round found a more favorable atmosphere for producing hail across northern Johnson County.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Riverton, WY wrote its last area forecast discussion before the first event at Jun 28, 10:30 AM MST, 2 hours 35 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 1130 AM MDT TUE JUN 28 2016 .SHORT TERM...Tuesday through Thursday night We are seeing a change this morning as we transition from a quiet pattern of the past few days into a more active one for the next three. Today looks to be the most interesting. The ridge that has brought the hot and dry weather of the past few days has sagged south a bit with heights lowering a bit. In addition, a weak shortwave will ride through the area and help to destabilize the atmosphere a bit. There are still some questions as for how strong the thunderstorms will get. Factors for the storms include a good amount of shear that could bring tilted updrafts and some stronger storms. There is also plenty of CAPE in the east with the models showing as much as 1500 J/KG in Johnson and eastern Natrona Counties with lifted indices down to minus 6. However, there are some inhibiting factors. Although 500 millibar heights will be a bit lower, they will still be over 5900 meters so it may take a while to break. The biggest limiting factor though is moisture though. The GFS keeps the 50 degree dew points out of the entire area except for eastern Johnson County. The NAM backs them in a bit further but only to around a Buffalo to Midwest line. In addition, the Storm Prediction Center has removed the slight risk from the area. As a result, we trimmed the severe area a bit. We followed to NAM 50 degree dew point line through most of Johnson County and eastern Natrona Counties. Elsewhere, with drier air and inverted V soundings, the main threat will be downburst winds and small hail With the timing changed to a bit later, we also raised temperatures a bit. Most of this activity should end by midnight as the wave moves away to the east. On Wednesday there will be more moisture over areas with better east to southeast flow. However, there will be less shear. The Storm Prediction Center only has general thunderstorms in the area as well. So for now, we went with small hail and gusty winds. The models also differ on the best coverage of the thunderstorms. The NAM shows a surge of moisture from the south. The NAM is the driest and has the best coverage in the north. The European has the best coverage in the east. So as a result we kept isolated over all areas with a better chance over Johnson County where the deeper moisture will be. A deeper plume of monsoonal moisture will move in for Wednesday night into Thursday. As a result we increased some showers across the area later Wednesday night into Thursday. This will also bring more cloud cover which will keep temperatures a bit lower. This looks to be the day with the best coverage of thunderstorms, although possibly the least chance of severe storms. .LONG TERM...Friday Through Tuesday Warm ridge axis over the area to start the period gradually flattens over the weekend leading to a potential shortwave passing to the north around Monday night which may push a decent front across the area. There looks like there will be quite a few 'ripples' in the flow but with limited moisture to work with resulting in mainly diurnally driven convection centered on the mountains during the afternoon with a few trying to move onto the lower elevations by the evening hours. Airmass will then dry out even more Monday into Tuesday with increasing sw flow Monday and a generally dry wly flow next Tuesday. Quite warm each day, especially Saturday through Monday when it looks like each day will be in the 90s for most areas east of the divide with upper 70s and 80s west. The high country will be in the 70s to lower 80s with 60s above 9500 to 10000 feet. Dry to very dry from the weekend onward with min rh's in the teens for most areas east of the divide with some increase in wind on the 4th leading to increased fire danger as combo of hot temps, breezy to windy conds and low rh's combine. && .AVIATION.../18Z Issuance/ Conditions will remain VFR through the forecast period. Shortwave topping the ridge and moving across Montana will help to initiate convection today, with the best coverage mainly north and east of a line from KCOD-KCPR. Small hail and localized MVFR conditions will be possible with the strongest storms. Best instability will be along and east of the Bighorn Range across Johnson County stretching into northeast Wyoming. Weaker convection will form over the east slopes of the western/central mountains and have left VCSH in those terminals. Showers and storms across this region are more likely to produce gusty outflow wind to 40kts with large temperature-dew point spreads. Convection will wane after 01Z-02Z/Wednesday as shortwave tracks east away from the forecast area. Could be a few lingering weak showers across the far north through 04Z with gusty outflow wind the main hazard. Gusty west-northwest surface wind 10-20kts anticipated after 20Z at KBPI and KPNA, while other terminals remain less than 12kts. && .FIRE WEATHER... ...Elevated fire conditions over southern Wyoming today... An upper level disturbance will cross the area today and bring a chance of mainly afternoon showers and thunderstorms, most numerous in northern and eastern sections. A gusty westerly wind and relative humidity falling into the teens will bring elevated fire danger across the south today. Near critical fire weather is possible in western Natrona County but red flag conditions are not expected. Strong to possible severe thunderstorms are possible in Natrona and Johnson Counties this afternoon and evening. Smoke dispersal and mixing will be fair to good east of the Divide and good to excellent across western and southern Wyoming. && .RIW Watches/Warnings/Advisories...None. && SHORT TERM...Hattings LONG TERM...PS AVIATION...CNJ FIRE WEATHER...Hattings
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 257 AM MDT TUE JUN 28 2016 WYZ001>020-022>030-291200- YELLOWSTONE NATIONAL PARK-ABSAROKA MOUNTAINS-CODY FOOTHILLS- NORTH BIG HORN BASIN-SOUTHWEST BIG HORN BASIN- SOUTHEAST BIG HORN BASIN-OWL CREEK AND BRIDGER MOUNTAINS- BIGHORN MOUNTAINS WEST-BIGHORN MOUNTAINS SOUTHEAST- NORTHEAST JOHNSON COUNTY-SOUTHEAST JOHNSON COUNTY- TETON AND GROS VENTRE MOUNTAINS-JACKSON HOLE- WIND RIVER MOUNTAINS WEST-WIND RIVER MOUNTAINS EAST- UPPER WIND RIVER BASIN-WIND RIVER BASIN-LANDER FOOTHILLS- GREEN MOUNTAINS AND RATTLESNAKE RANGE- NATRONA COUNTY LOWER ELEVATIONS-CASPER MOUNTAIN-STAR VALLEY- SALT RIVER AND WYOMING RANGES-UPPER GREEN RIVER BASIN FOOTHILLS- UPPER GREEN RIVER BASIN-SOUTH LINCOLN COUNTY- ROCK SPRINGS AND GREEN RIVER-FLAMING GORGE-EAST SWEETWATER COUNTY- 257 AM MDT TUE JUN 28 2016 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT ISOLATED TO WIDELY SCATTERED AFTERNOON AND EVENING THUNDERSTORMS ACROSS. SOME COULD BE STRONG TO SEVERE WITH STRONG GUSTY WINDS...LARGE HAIL...AND FREQUENT LIGHTNING...MAINLY IN JOHNSON AND EASTERN NATRONA COUNTIES. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY WEDNESDAY...ISOLATED TO WIDELY SCATTERED THUNDERSTORMS ACROSS THE NORTH AND EAST. THURSDAY AND FRIDAY...ISOLATED THUNDERSTORMS. SATURDAY AND SUNDAY...ISOLATED LATE DAY THUNDERSTORMS...MAINLY IN AND NEAR THE MOUNTAINS. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE URGED TO REPORT STRONG WINDS AND HAIL. THANK YOU. TEAM RIVERTON
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
145 PM MDT TUE JUN 28 2016
WYZ017>019-282030-
LANDER FOOTHILLS-WIND RIVER BASIN-GREEN MOUNTAINS AND RATTLESNAKE
RANGE-
145 PM MDT TUE JUN 28 2016
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN FREMONT COUNTY UNTIL
230 PM MDT...
AT 144 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR
RED CANYON...WHICH IS 10 MILES SOUTHEAST OF LANDER...MOVING EAST AT
30 MPH.
DIME SIZE HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH
THIS STORM.
THIS STRONG THUNDERSTORM WILL BE NEAR...
SAND DRAW AROUND 230 PM MDT.
OTHER LOCATIONS IMPACTED BY THIS STORM INCLUDE TWIN PINES RV PARK AND
CAMPGROUND.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
FREQUENT CLOUD TO GROUND LIGHTNING IS OCCURRING WITH THIS STORM.
LIGHTNING CAN STRIKE 15 MILES AWAY FROM A THUNDERSTORM. SEEK A SAFE
SHELTER INSIDE A BUILDING OR VEHICLE.
&&
LAT...LON 4257 10806 4262 10864 4264 10864 4266 10866
4264 10867 4268 10870 4281 10870 4284 10805
TIME...MOT...LOC 1944Z 270DEG 24KT 4272 10860
21SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 153 PM MDT TUE JUN 28 2016 WYZ011-282045- SOUTHEAST JOHNSON COUNTY- 153 PM MDT TUE JUN 28 2016 ...SIGNIFICANT WEATHER ADVISORY FOR EAST CENTRAL JOHNSON COUNTY UNTIL 245 PM MDT... AT 152 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 16 MILES NORTHEAST OF MAYOWORTH...WHICH IS 20 MILES NORTH OF KAYCEE... MOVING SOUTHEAST AT 20 MPH. HALF INCH HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH THIS STORM. THIS STRONG THUNDERSTORM WILL BE NEAR... FORT RENO HISTORICAL SITE AROUND 245 PM MDT. THIS INCLUDES INTERSTATE 25 BETWEEN MILE MARKERS 270 AND 279. THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR ADDITIONAL INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE. LAT...LON 4397 10672 4412 10659 4393 10609 4371 10630 TIME...MOT...LOC 1952Z 304DEG 18KT 4401 10658 21
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
205 PM MDT TUE JUN 28 2016
WYZ019-020-282045-
NATRONA COUNTY LOWER ELEVATIONS-GREEN MOUNTAINS AND RATTLESNAKE
RANGE-
205 PM MDT TUE JUN 28 2016
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN NATRONA COUNTY UNTIL
245 PM MDT...
AT 205 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR
ERVAY...WHICH IS 31 MILES NORTHEAST OF JEFFREY CITY...MOVING EAST AT
40 MPH.
HALF INCH HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH
THIS STORM.
THIS STRONG THUNDERSTORM WILL BE NEAR...
ERVAY AROUND 210 PM MDT.
OTHER LOCATIONS IMPACTED BY THIS STORM INCLUDE AUSTIN CREEK NATURAL
GAS PROCESSING PLANT.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
FREQUENT CLOUD TO GROUND LIGHTNING IS OCCURRING WITH THIS STORM.
LIGHTNING CAN STRIKE 15 MILES AWAY FROM A THUNDERSTORM. SEEK A SAFE
SHELTER INSIDE A BUILDING OR VEHICLE.
THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND
TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR ADDITIONAL
INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.
&&
LAT...LON 4268 10751 4293 10752 4293 10750 4298 10750
4296 10669 4265 10667
TIME...MOT...LOC 2005Z 267DEG 35KT 4283 10744
21The Riverton/Lander radar (KRIW), 94 km away, was scanning. The volume nearest the first event began at 20:06 UTC.
1 thunderstorm wind, 1 hail. Local standard time, as filed.
Quick-moving showers and thunderstorms aligned in a broken line from Johnson County southwestward into Fremont County. One thunderstorm generated outflow wind that produced a 64 mph wind gust at a mesonet sensor near Hiland.
A thunderstorm rapidly intensified along and downstream of the Bighorn Mountain foothills northwest of Buffalo. The storm tracked southeast through Saddlestring where the public reported nickel-sized hail at a rural ranch along Rock Creek.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2016Every state in 2016This day in weather historyWarnings in Wyoming, June 2016
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 634111, 634112.