Heavy rains brought by a strong plume of monsoonal moisture caused flooding across Sweetwater and Natrona counties in southern and eastern Wyoming on August 2nd, and into August 3rd. Heavy storms moved through Sweetwater county ar around 500pm on the 2nd, with the ASOS at Rock Springs reporting around 0.69" in an hour. A call to the National Weather Service from the Sweetwater County’s Sheriff’s Office around 530pm relayed flooding around Superior on Interstate-80. Reports of this flooding continued through around 7pm when storms had settled. However...another storm moved through beginning around 930pm dropping another 0.47" by midnight bringing a total of around 1.16" of rain at the airport. Localized areas saw increased rainfall amounts than received at the airport. This secondary storm prompted another Flash Flood Warning to be issued around 10 pm. This warning covered the majority of southeastern Sweetwater county, with concerns of an additional 2 inches of rain. Reports have been made to the National Weather Service in Riverton the morning of August 3rd have confirmed flooding across portions of Sweetwater County (around the Bitter Creek area - from Point of Rocks to Thayer Junction).
A thunderstorm moved over southeastern Natrona County around 8 pm, which was capable of producing nickel sized hail, and damaging winds to 60 mph. Consequently, a severe thunderstorm warning was issued around 8pm and was effective until 930pm. If you witnessed this storm and measured or have a reference measurement on hail sizes which occurred during the aforementioned warning time, please call the NWS in Riverton at 1-800-211-1448. We appreciate all reports.
As this thunderstorm moved through the area, it produced very heavy rainfalls, with radar estimates by 817pm on August 2nd reaching 3 inches, with additional rainfall possible of 1 to 2 inches. This was confirmed around 9pm when a trained spotter in the Casper area notified the NWS in Riverton of flooding around 12 Mile Road and the Poison Spider Road. Subsequent reports of flooding in these areas continued through the late evening hours. At 11pm strong reports filtered in from an Emergency Manager informed the NWS Riverton that Poison Spider School had flooded - with an estimate of $100,000 worth of damage. Flooding in these areas finally subsided by 2 am. Reports of storm totals found on the morning of August 3rd had a maximum rainfall report of 2.09" at 4.3 miles west-southwest of Casper (over a 24 hour period). Similar reports over an inch were also reported throughout Natrona County... with final radar estimates of around 3 to 4 inches of rainfall over flooded areas.
During the evening of August 3rd, Doppler Radar indicated another 1.25 inches of rain had fallen between 5 and 6pm, with additional rainfall expected during the evening hours. Because of these rainfalls, another Flash Flood Warning was issued around 6pm, and encompassed much of the Casper area. At 630pm the Doppler Radar indicated that 2 inches of rain had fallen along Poison Spider Creek, with around another 2 inches of rainfall possible throughout the evening hours. Reports began to come into the NWS in Riverton around 7 pm - with 0.6" of rain being reported within 15 minutes just northeast of downtown Casper. Additional reports came in to the NWS which reported 1.38" of rain fell inside 20 minutes at 2.5 miles northeast of Casper...with another report of 1.25" in 30 minutes on the north edge of downtown Casper. At 8 pm, Natrona County Emergency Management officials notified the NWS of flooding around the Paradise Valley Area, and the Poison Spider Road. Rainfall, by this time, had subsided over the warned area though flooding concerns remained elevated as runoff from the evening’s storms continued to move into the affected areas. Around 10 pm, the NWS in Riverton was notified that flooding had subsided around the warned area, and the concerns were done for the evening.
Remember to not drive or walk through flooded roadways or walkways, as it will be impossible to determine the amount of road damage below seemingly innocent puddles. If flood conditions continue, move to higher ground, and remain there until it is known the flooding has subsided enough for safety!