The Weather Wire
May 2007 Volume 15 Number 05
Avg High 59.9
Avg Low 33.6
Snow - 0.9"
Season Snow - 72.6"
Precipitation - 2.65"
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 change, or perhaps improvement, in overall drought conditions across Colorado occurred in April.
The map below shows forecasted temperature deviances for May 2007. As can be seen, .normal temperatures are expected for Colorado for May 2007.
The map below shows forecasted precipitation deviances for May 2007. Normal precipitation is expected for Colorado for May 2007.
As can be seen in the below map, drought improvement is forecast for portions of far Northeast Colorado through July. Some drought persistence will continue far Western Colorado.
Between April 23 and 24, 2.10 inches of rainfall was recorded at DIA. This is a 24 hour precipitation record surpassing the old record of 1.29 inches set back in 1891. The month finished with a total of 2.65 inches which was 0.72 inch above normal. So, now 3 of the past 5 months have been above normal in the moisture category. April is Denver’s 3rd snowiest month. However at the old Stapleton’s recording site only 0.9 inch was recorded. Again most areas along the Front Range had much more snow than that! We continue well above normal for the season with a total of 72.6 inches, 10.9 inches above the normal of 61.7. Many areas of the western and southern suburbs are well above 100 inches for the season.
Temperatures during April 2007 ranged from a high of 83 degrees down to a low of 22 degrees. The average temperature for the month was 46.8 degrees which was 0.8 degrees below normal. The coldest April occurred in 1920 with an average temperature of 38.8 degrees.
The weather in Denver is quite changeable throughout the year. However, the month of May seems to feature the most changes from year to year, day to day or even hour to hour. Denver’s May weather can include almost any type of weather.
Late season frosts can nip plant growth because the average date of the last freeze is May 5th, but the latest date of a Denver freeze is June 2. On the other hand, afternoon temperatures in the 80s are common and the mercury occasionally climbs into the 90s.
May normally marks the beginning of the severe weather season. Violent thunderstorms with large hail and tornadoes are possible. These severe storms occur when moisture from the Gulf of Mexico moves into Colorado and collides with cold fronts still moving in from Canada or from the Pacific Northwest.
May is also the wettest month of the year and on average, precipitation normally occurs once every three days. May is tied with November as having the lowest percentage of possible sunshine.
Snowfall in Denver during May is rare but does occur as we saw last May. Denver’s high elevation intensifies late season cold air masses and on the average snow occurs in about two out of every five years.
Sunrise/Sunset (Denver area)
October 2006 to April 2007