National Weather Service Weather Forecast Office

Areal Climate Summary for the Year 2011

The year 2011 for this region turned out to be generally a little cooler than normal.  Rainfall was generally near to above normal, with some notable extremes.       

The year was characterized in general by a cool late winter and spring, mild and wet conditions in the late spring into early summer transitioning to very warm and dry conditions from mid-summer into fall, then closing out closer to normal.  The overall weather pattern was affected by the presence of La Nina, which was at moderate to strong strength early in the year.  It dissipated for a time by summer but reappeared at weak to moderate strength in the fall.

Temperatures:
 
Average temperatures across the region for the year turned out to be a little cooler than normal, with the central and northern Nebraska panhandle being a little warmer than normal. Much of the warmer than normal average there can be attributed to very warm temperatures in July and August.  The following table summarizes the average annual temperature, average daily high and low temperatures, and the departures from normal for select sites over the area:

* based on new normals for the period 1981-2010.

The warmest and coldest temperatures of the year and the number of days with highs 90 or higher and lows of zero or lower are depicted for select cities in the following table:

Precipitation:

Precipitation across the area was generally near to above normal, though a significant amount of the precipitation fell in the first half of the year, with the second half somewhat on the dry side.     There were some extremes of note.  Sidney, Nebraska recorded their wettest summer on record as an impressive 16.19 inches of rain was recorded in June through August.  Cheyenne recorded its 2^nd wettest July on record with 5.63 inches of rainfall.  At the other extreme was Chadron Nebraska which had a very dry summer.  Only 2.48 inches recorded there. In addition, it was the driest August on record for Chadron as only a trace of rainfall was recorded in that month.

The following table tabulates the 2011 precipitation and snowfall amounts, departures from average and the percent of normal:

* based on new normals for the period 1981-2010

Other Notable Weather Events during 2011:

- Significant river flooding occurred in late spring into early summer due to snow melt from unusually high snowpack over the mountains.

- First severe thunderstorm event over the area occurred on May 9^th over east central Wyoming and the northern Nebraska Panhandle.  Hail up to 2.75 inches in diameter fell south of Chadron while a brief tornado was spotted east of Harrison, Nebraska.

- Damaging hail up to 1.75 inches in diameter fell in Sidney on June 13^th resulting in many broken windows.

- Severe hailstorm struck Cheyenne on July 12^th resulting in widespread damage to roofs and vehicles with hail up to 2 inches in diameter.  Over 2 inches of rain fell in about ½ hour as well resulting in some flooding.

- Last severe thunderstorm event occurred on August 29^th with some large hail and a brief tornado over the extreme northern Nebraska Panhandle.

- A couple of significant early season snows occurred in October.  The first occurred on October  8^th at elevations generally above 6000 feet.  The snow was rather heavy and wet and caused tree limbs to snap and in some cases fall onto power lines which resulted in power outages, especially northwest of Cheyenne.  Snowfall amounts from 3 to 8 inches were common in these areas.  A second heavy snow occurred on the 25^th into the 26^th and produced generally 5 to 10 inches across parts of the area.

- High winds over parts of the area December 29^th and 31^st with gusts to 77 mph measured in Cheyenne and up to 90 mph northwest of Cheyenne.  The winds caused some damage to roofs as well as blew over several trucks on roads.  The winds gusts were ranked in the top 10 strongest on record for Cheyenne.