An abnormally strong upper level low and strong winds aloft moved across western Wyoming on the afternoon of Monday, July 27. In addition, a tight pressure gradient generated high wind both ahead of and just behind the passage of a vigorous cold front. The most severe storm of the day tracked northeast across Big Horn County producing large hail and strong wind. Wind gusts of 60 to 76 mph also occurred with much weaker convection given favorable surface temperature-dew point spreads in combination with the pressure gradient. Ahead of the front, gradient winds were strong enough to topple trees, rip limbs, and cause damage in Riverton where a peak gust of 59mph was registered at 1503MST.

Hail in BIG HORN, WYOMING
From 27-JUL-15 14:43:00 to 27-JUL-15 14:43:00 (MST-7)
Location: BURLINGTON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Quarter sized hail was reported in Burlington.

Thunderstorm Wind in WASHAKIE, WYOMING
From 27-JUL-15 14:50:00 to 27-JUL-15 14:50:00 (MST-7)
Location: NOWOOD
Magnitude: 66.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

Weak convection and a strong pressure gradient combined to produce a peak wind gust of 76 mph shortly before 1500MST at the Split Rock Creek RAWS.

Thunderstorm Wind in HOT SPRINGS, WYOMING
From 27-JUL-15 15:40:00 to 27-JUL-15 15:50:00 (MST-7)
Location: THERMOPOLIS
Magnitude: 58.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several wind gusts over 58 mph were recorded at Thermopolis with a peak speed of 67 mph. The gusts were the result of weak convection and a strong pressure gradient ahead of an approaching cold front.

Thunderstorm Wind in NATRONA, WYOMING
From 27-JUL-15 15:50:00 to 27-JUL-15 15:54:00 (MST-7)
Location: (CPR)NATRONA CO ARPT
Magnitude: 54.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Weak convection coupled with a tight pressure gradient combined to produce wind gusts of 59 and 62 mph at the Casper-Natrona County International Airport.

Hail in BIG HORN, WYOMING
From 27-JUL-15 14:48:00 to 27-JUL-15 14:50:00 (MST-7)
Location: EMBLEM
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Hail up to the size of golf balls was reported near Emblem.

High Wind in Wind River Basin, WYOMING
From 27-JUL-15 14:50:00 to 27-JUL-15 15:03:00 (MST-7)
Magnitude: 51.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: ASOS

Westerly pre-frontal winds ahead of an approaching cold front reached 59 mph at Riverton Regional Airport. Numerous limbs were downed around Riverton. Two trees were also toppled in town with one falling on a power line.

Thunderstorm Wind in BIG HORN, WYOMING
From 27-JUL-15 14:55:00 to 27-JUL-15 15:55:00 (MST-7)
Location: COWLEY ARPT
Magnitude: 55.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

The AWOS at the North Big Horn County Airport near Cowley had several wind gusts in excess of 60 mph between 1455 and 1555MST. The wind was primarily from the northwest with the strongest gust being 63 mph at 1455MST. The wind gusts were the result of weak convection combining with already gusty surface wind associated with a cold frontal passage.

Thunderstorm Wind in BIG HORN, WYOMING
From 27-JUL-15 15:42:00 to 27-JUL-15 16:01:00 (MST-7)
Location: GREYBULL ARPT
Magnitude: 64.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Wind gusts associated with a strong cold front and weak convection reached 74 mph at the South Big Horn County Airport just north of Greybull.