The Weather Wire
May 2008 Volume 16 Number 05
Avg High 61.6
Avg Low 30.6
Snow - 2.9"
Season Snow - 42.9"
Precipitation - 0.32"
Avg High 70.5
Avg Low 43.8
Avg Snow - 1.3"
Avg Precip - 2.32"
Lightning Season Again!!!
Yes it is that time of year again! Usually March brings the first claps of thunder and the first bolts of lightning. If not in March, definitely in April and May. On average some 20 million bolts of lightning strike the U.S. during a single year. Of these over half strike the ground at more than one point. So we have at a minimum 30 million spots struck by lightning each year! That is a lot of lightning! The lightning capital of the nation is Florida, but Colorado is not far behind. This is due to our closeness to the mountains to our west. The mountains help to trigger thunderstorms for our area spring through fall. A typical thunderstorm day for Colorado starts out with a sunny morning. Clouds begin to develop on the mountains and foothills to the west. As the clouds grow taller and develop into thunderstorms upper level steering winds push the storms out onto the plains.
Lightning is caused as rising air currents in the storms carry water droplets to areas of the clouds below freezing, where some of these droplets freeze. It is in the mixture of water and ice that a charge develops. When this charge is sufficiently large a bolt of lightning reaches from the cloud to the ground releasing large amounts of electricity. In the tropics where the atmosphere is warmer to a higher altitude many storms can and do produce torrential rains but produce no lightning so having a low altitude freezing level such as we have here in Colorado increases the number of lighting strikes we see along the Front Range. This low freezing level is also conducive to producing hail, which we see quite a bit of in eastern Colorado.
Cloud to ground lightning can kill or injure people by direct or indirect means. The lightning current can branch off to a person from a tree, fence, pole or other tall object. In addition, lighting strikes may conduct their current through the ground to a person after the lightning strikes a nearby tree, antenna or other tall object. The current also may travel through power or telephone lines, or plumbing pipes to a person who is in contact with an electric appliance, telephone or plumbing fixture. Now lets think about the golfer who is carrying a metal rod and wearing spikes shoes, not the best combination when there is lightning around!
During the past 30 years, lightning killed an average of 73 people per year in the United States based on documented cases. This is more than the average of 68 deaths per year caused by tornadoes and the average of 16 deaths per year caused by hurricanes. However, because lightning usually claims only one or two victims at a time, and because lightning does not cause the mass destruction left in the wake of tornadoes or hurricanes, lightning generally receives much less attention than the more destructive weather-related killers. While documented lightning injuries in the United States average about 300 per year, undocumented injuries caused by lightning are likely much higher.
One of the factors here in Colorado that causes a false sense of security and causes many people to stay out too long is our naturally dry air. Many times thunderstorms develop, the rain falls from the clouds, but evaporates before it gets to the ground. Lighting is still produced in these ‘dry’ thunderstorms, but with no rain to chase people indoors the tendency to stay outside until it is too late. In addition lighting has been know to strike as far as 10 miles from the approaching storm. So just because it is not raining yet, does not mean you are safe from lightning!! You should always stay alert to changing weather conditions while you are outside and have a good idea where you will go if lighting becomes a threat.
The most important statement for everyone to understand, memorize and act on is: NO PLACE OUTSIDE IS SAFE FROM LIGHTING NEAR THUNDERSTORMS!!
Little in the way of meaningful drought across Colorado as of early May though some dry areas do persist across Eastern Colorado.
The map below shows forecasted temperature deviances for May 2008. As can be seen, much of northern and central Colorado is expected to have below normal temperatures for May 2008.
The map below shows forecasted precipitation deviances for May 2008. Normal precipitation is anticipated across most of Colorado, with extreme northeastern Colorado forecast to have slightly above average precipitation.
Little change in conditions is anticipated over the next 3 months, with most of the state not expected to see drought conditions. Extreme southeastern Colorado is anticipated to experience drought conditions persisting and possibly intensifying.
April of 2008 was one of the driest in Denver history with only 0.32" of precipitation becoming the 5th driest April on record. For the year Denver is now nearly 3.5" of precipitation below normal and this will be very difficult to make up. For snowfall only a meager 2.9" was reported at the Stapleton site which is 6.2" below the normal value of 9.1". Looks like the Stapleton site will end up around 18" below normal in snowfall while many other areas west and south of town are at or slightly above normal. Despite the lack of precipitation the skies were unusually cloudy with only 55% of possible sunshine which is well below the average of 67%. Temperatures were slightly above average for highs with 61.6 degrees as compared to 60.9 degrees on a normal year. Lows on the other hand were below normal with 30.6 degrees compared to 34.2 on average. The monthly mean was below average by 1.5 degrees which is keeping the streak going for at or below normal temperatures going all the way back to December. The dry month and periods of strong winds resulted in an unusually high amount of fire weather watches and warnings. Three firefighters have already lost their lives this year and is the most in the state since the Storm King Fire in western Colorado all the way back in 1994 when 14 firefighters were lost.
May can be an unpredictable month along the Front Range of Colorado which can feature late season snowfall and hard freezes as well as warm and sunny days or rain showers and afternoon thunderstorms. The last freeze is "normally" around May 5th but can be as late as June 8th. Believe it or not, May is also the wettest month here in Denver with 2.32" of precipitation on average and we will need all of it and then some to begin to catch up in our deficit so far this year. It can happen as May is the wettest month in Denver history with 8.57" back in 1876, however with the current weather pattern the chances are next to zero. Thunderstorms become more numerous in May with 6 thunderstorm days on average. Last May of 2007 was very active with 17 thunderstorm days. Typically 11 days of the month will feature measurable precipitation which about one out of every three days. So far 0.7" of snow has been recorded on the 1st of this month and average is only about 1.5". High and low temperatures climb significantly in May with temperatures in the 70s during the day and low to mid 40s overnight.
Sunrise/Sunset (Jan - June Denver area)
October 2007 to April 2008