Winter Weather Awareness Week
December 7-11, 2009

Intro

Monday

Tuesday

Wednesday

Thursday

Friday

Information on Backcountry Safety

Downslope Windstorms :

Windstorms occur in Nevada several times during the year but most commonly occur over and to the lee of the Sierra-Nevada Mountains. During these windstorms, peak gusts are typically 50 to 70 mph. However, with the more extreme windstorms, wind gusts can reach well over 100 mph and cause widespread damage. These windstorms occur when the strongest winds in the jetstream move directly overhead and while the atmosphere is considered to be “stable”. As the winds flow over the Sierra, they create “mountain waves” which allow these much stronger winds aloft to surface. Also, there are areas where winds speeds are enhanced due to local effects such as channeling through mountains and valleys as well as from a unique phenomenon known as a “hydraulic jump” where winds accelerate down the eastern slopes like water in a stream flowing over a rock. Lee-side wave clouds and lenticular clouds are often a sign that strong winds are overhead and will likely reach the surface, if they haven’t already.

Lenticular clouds over the Sierra which are indicative of strong winds.

The greatest number of injuries and fatalities during windstorms occur from motor vehicle accidents. Strong wind gusts, especially on north-south routes such as Highway 395, often catch motorists off guard and move their vehicle unexpectedly. Also, high profile vehicles, such as semi-trucks, often overturn, creating multi-vehicle accidents. In Nevada, strong winds can create dust storms which often reduce visibilities to less than one quarter mile and make it difficult for drivers to see. Trees blowing down or becoming uprooted are another significant threat to life and property. Power lines often come down during high winds which can lead to electrocution and also start wildfires. Less significant injuries from windstorms result from objects becoming airborne such as roof shingles, branches, rocks/sand, lawn furniture, and other unsecured outdoor items.

Strong winds associated with a dry cold front spreading blowing dust south through Nevada on April 28, 2004.

When windstorms are forecast, loose outdoor items should be secured and emergency supplies should be on hand in case the power were to go out. People that must travel during periods of strong winds should drive with extreme caution and slow down while leave extra space between vehicles, especially along north-south routes.

Damage sustained to a vehicle during a strong wind storm.

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