The Weather Wire
August 2010 Volume 17 Number 08
Avg High - 89.3
Avg Low - 59.5
Snow - 0.0"
Season Snow - 0.0"
Precipitation - 3.70"
Avg High - 88.0
Avg Low - 58.7
Avg Snow - 0.0"
Avg Precip - 2.16"
When will Thunderstorm Season Come to an End?
Actually, the summer thunderstorm season is already beginning to wind down now that we are past the first week of August but it will be another month plus a week or two before the Front Range experiences a major drop off in thunderstorm activity. There are 2 major reasons why the thunderstorm season shuts down by mid September: 1. Loss of daytime heating 2. Monsoonal moisture pushed southward.
The loss of daytime heating due to shorter and shorter days is a major reason why thunderstorms become less likely and weaker. The atmosphere above the surface still retains the heat of summer but the air near the ground is beginning to cool which results in a more stable air mass. This is due to the fact that warm air rises and if the air at the surface does not warm sufficiently it will not be able to rise thus no storm clouds are created. Even if the air does warm enough to rise it will not rise with as much force as earlier in the summer when temperatures aloft were cooler and there was a greater temperatures difference between the air aloft and at the surface. This results in the storms that do develop being weaker and less likely to produce severe weather. Moderate and heavy rainfall becomes the greatest threat from late season thunderstorms.
The monsoon moisture that typically arrives in the first week of July from the Desert Southwest has a much more difficult time remaining in place over Colorado as Pacific storm systems become stronger and more numerous pushing the monsoon moisture further and further south. The northern storm track becomes energized as temperatures at the North Pole begin to cool while the lower latitudes remain warm creating a larger temperature gradient from north to south. This temperature gradient fuels the jet stream allowing for more potent storm systems to move onto the west coast which eventually move into Colorado and literally sweep the monsoon moisture away from the state. Ahead of these disturbances moisture can be lifted northward resulting in a day or two of active weather but behind these disturbances a north to northwest flow pushes the moisture back to the south. This keeps the potential for prolonged wet weather at bay with more dry days than days with precipitation.
With the widespread precipitation of the last several months few areas of drought remain over Colorado, though some dry areas have developed in western Colorado.
The map below shows forecasted temperature deviances for July 2010. As can be seen, normal temperatures are expected the eastern 2/3s of Colorado with above average temperatures the western 1/3 of the state.
The map below shows forecasted precipitation deviances for July 2010. Normal precipitation is expected for the eastern 2/3s of Colorado with below normal precipitation the western 1/3 of the state.
Little in the way of drought remains in Colorado.
July of 2010 was very wet for most areas of the Front Range as DIA reported 3.70” of precipitation for the month and 13 days with measurable rainfall. Normal precipitation for DIA is 2.16” and with a surplus of 1.54” for July we are now 0.25” above normal for the year. This July missed out on being in the top ten wettest July’s ever recorded by only 0.01” out of 10th place. What a difference a month can make! July of 2010 was also a little warmer than average with a mean temperature of 74.4 degrees compared to 73.4 on average. There were 18 days with high temperatures of 90 degrees or more with 15 days during an average July.
August is typically the last month of true “summer” along the Front Range as temperatures towards the end of the month begin to fall off and thunderstorms become less likely. Upper level winds are typically quite light this month reducing the necessary wind shear for severe storms with slow moving moderate and heavy rainfall producing thunderstorms being most likely which are fed by monsoonal moisture being drawn northward from the Desert Southwest. The average high for August is 86.0 and the average low is 57.4 producing a monthly mean temperature of 71.7 which is cooler than July. Average precipitation for the month is 1.82” with 9 days of measurable precipitation. The record high for the month is 105 degrees which is tied for the hottest in Denver history and the record low is 40. August of 2010 will likely be around normal in both precipitation and temperature.
Sunrise/Sunset (July - Dec Denver area)
May 2010 to Sept 2010