The Weather Wire
October 2004 Volume 11 Number 10
Avg High 77.6
Avg Low 44.7
Snow - 0.0"
Season Snow - 0.0"
Precipitation - 1.99"
Avg High 66.0
Avg Low 35.9
Avg Snow - 4.1"
Avg Precip - 0.99"
St. Helens and Weather... |
With Mt. St. Helens becoming active again after almost 20 years a little volcano weather would be rather topical. Mt. St. Helens is located in the Cascade Mountain range and is one of many volcano’s that ring the west coast of the Untied States. Right now she is one of the few active volcanoes in the continental U.S.. Mt. St. Helens has its origins going back millions of years and was formed due to continental drift. The pacific plate is diving under the U.S. continental plate. Where these two plates collide they generate tremendous amount of heat, hot enough to melt solid rock. This is where we see numerous volcanoes along this line of colliding and heating plates.
Now I’m sure just about everyone has see films or pictures of Hawaii’s volcanoes. Where hot molten rock flows out of the volcano and down its slopes in large lava flows. Mt. St. Helens is a different type of volcano and has a totally different type of eruption. The lava in St. Helens has a vast amount of gas and steam in it. As the lava breaks the surface this gas expands explosively and cools. This process cools the lava quickly back to a solid and then shatters the cooled lava into thousand of small rocks and millions of particles of volcanic ash. With this type of volcano we never see a lava flow, but explosive eruptions that throw tons of material into the atmosphere. Those are the basics of the volcano. Believe me it is much more complicated than that, but we are not volcanologists, we are weather forecasters. So how does this erupting volcano play a part in our weather??
All volcanoes emit large amounts of water and CO2 into the atmosphere. CO2 is a green house gas and has been a hot topic with the global warming set. Long before people walked on this planet, volcanoes put large amounts of CO2 into the air. It is one theory that during the age of the dinosaurs when the climate was quite tropical for much of the globe that a very active volcanic period preceding the dinosaurs and changed the climate to one of warm and tropical very much suitable to the dinosaurs. So in some ways global warming is not a new phenomenon. This is just one way volcanoes can affect the weather.
Getting back to the type of Volcano we have in Mt. St. Helens. The eruptions of the past few days have been minor with more steam being vented than ash. When St. Helens blew its top in 1980, literally thousands of tons of volcanic material was thrown into the atmosphere. Some of that volcanic dust even made it way to Denver and the Front Range. Giving us more than a few hazy days and also providing us with some spectacular sunsets. More importantly tons of that dust made its way 50-80 thousand feet into the atmosphere and circled the globe in the stratosphere. The dust particles literally spread out over the entire world. Once in the upper parts of the atmosphere the dust particles acted like millions of tiny mirrors reflecting light from the sun back into outer space. Since sunlight is our source of heat from the sun, having some of it reflected back away from us had a cooling influence over the weather for the next couple of years. The weather records here in the United States actually do show a slight cooling in the two years after the eruption.
In the grand scale of Mother Nature what we saw with Mt. St. Helens in 1980 was a small time eruption. In our geologic past were many much larger volcanic eruptions having a much larger effect on the weather for planet earth and some of those effects lasted centuries not just a couple of years.
Fortunately we no longer see major volcanic outbreaks like in our distant past that made major changes to the earths weather, but even the ones we have, like Mt. St. Helens can have an impact on our weather, however, in absence of an extreme eruption occurred in 1980, it is very unlikely that Mt. St Helens will impact the weather patterns of Colorado, or the United States.
In many portions of Colorado, September 2004 continued to see above normal precipitation, particularly across Eastern Colorado. With the moisture, the drought situation improved across much of Colorado.
The map below shows forecasted temperature deviances for the October 2004 time period. As can be seen, above normal temperatures are expected for all of Colorado for October.
The map below shows forecasted precipitation deviances for October 2004. Normal or near normal precipitation is expected for October 2004 all of Colorado.
As can be seen in the below map, drought conditions are expected to continue to improvement across much of Colorado through December2004.
4th month in a row with above normal Precipitation
Denver has notched its 4th month in a row with above normal precipitation. In fact, Denver is currently above normal through September for the year so far with 13.32 inches, which is 0.11 inch above the normal of 13.21 inches. The last time Denver recorded 4 months in a row of above normal in the rainfall category was in 1995 covering the period of April, may, June and July. The 24 hour maximum precipitation during September was 0.91 inch which occurred on September 4th, but was not a 24 hour record. There were 8 days with measurable moisture, which is 2 days above normal. The 1.99 inches of rainfall was not near enough to get into the top 10 wettest Septembers, 2.27 inches holds down the number 10 spot recorded both in 1970 and 1940. The wettest September was 4.67 inches in 1967.
Temperatures for the month of September 2004 were pretty much normal. The month finished 0.3 degrees above the normal of 62.4 degrees. There were only two 90 degree days which were exactly 90 degrees and both were the warmest days during September. The normal number of 90 degree days for September is 2. Temperatures ranged from the two 90 degree readings down to 37 degrees. There were no temperature records set or tied during the month.
No severe weather was observed at DIA during September. Eight thunderstorms were recorded and all except one were accompanied by rainfall. No hail was observed at DIA for the month.
So with the exception of above normal rainfall September 2004 was pretty much the norm.
October is normally one of the quietest weather months in Denver with an abundance of mild sunny days and clear cool nights. It has the second highest amount of sunshine with 72 percent. The month with the highest percentage is September with 74 percent and coincidently the month after October, November is one of the lowest sunshine months with only 64 percent. In most years October brings the first taste of winter with the average date of the first freeze on the 7th and the average first snow on the 15th.
There is a great temperature extreme difference for October. The record high October Temperature is 90 degrees set October 1st 1892, while the coldest October temperature is 2 degrees below zero set on October 29th 1917. On October 2nd 1969 the Denver temperature was 85 degrees. On October 3rd and 4th 15 inches of snow fell across the metro area. In 1991 a record high or 89 degrees was set on the 16th followed by lows of 7 degrees on the 30th and 10 degrees on the 31st.
One of Denver’s most famous snowstorms was the “Bronco Blizzard” which occurred on October 15th 1984. This storm was witnessed by a nationwide television audience on Monday night football. By the time the game ended the entire field was covered by 3-4 inches of snow. By the time the storm ended over a foot of snow had fallen over most of the metro area. October 1997 turned out to be a snow record setter. The blizzard of October 24th-25th produced 19.1 inches of snow in a 24 hour period setting a new October record. Before the storm ended 21.9 inches of snow had fallen at old Stapleton Airport during the 2 day period. The month finished with 22.1 inches making it the 3rd snowiest October in Denver history.
Sunrise/Sunset (Denver area)