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Severe weather expected on Flag Day; Cheyenne prepares for storms

Thunderstorm (Shutterstock)

CHEYENNE, Wyo. — After recording a new high of 93 degrees on June 13, Cheyenne and the high plains of southeast Wyoming are bracing for strong to severe thunderstorms today. As Flag Day and the U.S. Army’s Birthday celebrations unfold, the National Weather Service in Cheyenne is warning of heavy rain, possible flash flooding, large hail and damaging winds.

The NWS in Cheyenne issued a slight risk for severe weather for much of the Nebraska Panhandle. Current observations show south to southeasterly winds across much of the area east of the Laramie Range. These winds will bring low-level moisture into the region, raising dew points into the afternoon.

The storms are expected to develop around mid-afternoon. Initial storms may produce large hail, as the atmosphere will have enough energy to fuel strong thunderstorms. This energy is measured as “MUCAPE,” or Most Unstable Convective Available Potential Energy. High MUCAPE values, measured in Joules per kilogram, indicate a greater potential for severe storms. In this case, values in the panhandle approach 2,000 J/kg, which is quite high.

As the storms move east, they are likely to cluster together, increasing the chance of isolated gusts over 60 mph. Wind shear, or changes in wind speed and direction with height, will be in the 35–40 knot range or around 40–45 mph. This means the wind speeds at different heights will be strong and varied, which can help storms become severe. An isolated tornado cannot be ruled out in the southern Panhandle due to these conditions.

Heavy rain is a significant concern. NWS in Cheyenne models show Precipitable Water, or PW, values over an inch. PW is a measure of how much moisture is in the atmosphere, and values over an inch indicate a high potential for heavy rain. The storms are expected to move quickly, but they can still drop large amounts of rain in a short period, increasing the risk of flash flooding.

The potential for severe storms will drop off around 9 p.m., but scattered showers and thunderstorms will linger overnight. Conditions on Saturday will dry out and warm up, with highs in the upper 80s and 90s east of the Laramie Range. A weak upper-level disturbance may cause thunderstorm development in the afternoon, but much of the precipitation may not reach the ground, leading to strong, gusty winds.

Looking ahead to Sunday and Monday, isolated to widely scattered thunderstorms are expected in the late afternoon through the late evening. No severe weather is anticipated, but a few strong thunderstorms are possible north of Interstate 80. Highs will remain in the 80s along I-80 and west of I-25. Temperatures may struggle to reach the mid-70s from Douglas to Chadron.

A late-season Pacific cold front is expected to arrive Tuesday night, bringing cooler temperatures. Highs will be in the mid-60s to mid-70s on Wednesday, with some areas potentially seeing lows near freezing. A warming trend is expected later in the week, with more favorable conditions for afternoon and evening thunderstorms.

Detailed Forecast for Cheyenne

  • Flag Day: Showers and thunderstorms are likely, mainly after 3 p.m. The weather will be mostly cloudy, with a high near 81. There will be a south-southwest wind at 5–10 mph. The chance of precipitation is 60%, with new rainfall amounts between a quarter-inch and a half-inch possible.
  • Tonight: There is a 30% chance of showers and thunderstorms, mainly before 9 p.m. The sky will be mostly cloudy, with a low around 56. There will be a south-southwest wind at 10–15 mph, shifting to the west after midnight.
  • Saturday: There is a 30% chance of showers and thunderstorms after noon. The weather will be mostly sunny, with a high near 88. There will be a west wind at 10–15 mph.
  • Saturday Night: The sky will be mostly clear, with a low around 53. A southwest wind at 5–10 mph will shift to the north-northwest after midnight.
  • Sunday: The weather will be sunny, with a high near 86. A north-northwest wind at 5–15 mph will shift to the south-southeast in the afternoon. Winds could gust as high as 30 mph.
  • Sunday Night: The sky will be partly cloudy, with a low around 52.
  • Monday: The sky will be mostly sunny, with a high near 83.
  • Monday Night: The sky will be partly cloudy, with a low around 49. It will be breezy.
  • Tuesday: There is a slight chance of showers and thunderstorms after noon. The weather will be sunny, with a high near 76. It will be breezy.
  • Tuesday Night: There is a chance of showers and thunderstorms before midnight. The sky will be mostly cloudy, with a low around 44.
  • Juneteenth: There is a slight chance of showers and thunderstorms. The weather will be mostly sunny, with a high near 71.
  • Wednesday Night: There is a slight chance of showers and thunderstorms. The sky will be partly cloudy, with a low around 48.
  • Thursday: There is a chance of showers and thunderstorms. The weather will be mostly sunny, with a high near 78.

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