The Weather Wire
August 2004 Volume 11 Number 8
Avg High 85.0
Avg Low 56.7
Snow - 0.0"
Season Snow - 0.0"
Precipitation - 2.33"
Avg High 82.1
Avg Low 53.0
Avg Snow - 0
Avg Precip - 1.56"
Although noticeably absent the past 5-6 years due to the drought across the west, the Colorado monsoon season has arrived. Most people associate monsoons with parts of Asia and India but we do have monsoons right here in Colorado.
The word monsoon is used to describe a reoccurring seasonal weather pattern. In Asia during the winter months cold high pressure dominates the continent and the general airflow is off the continent out over the Pacific Ocean. This is a general dry pattern the affects not only Asia but, Southeast Asia and India. During the summer months the large land areas of Asia heat up. This causes the air to be heated and then rise. Warm moist air from the Pacific Ocean and Indian Ocean now moves in to try to replace the rising warm air. As this warm moisture air moves in and rises with the topography clouds and rain are the result. This happens at about the same time every year and can cause serious flooding in many areas.
Now the mechanism that bring the Colorado monsoon is slightly different, but does occur just about every season at about the same time during the summer. Typically from mid July to almost the end of August is the monsoon season for not only Colorado but, much of the Southwest United States.
The weather pattern that sets this up is a ridge of high pressure becoming semi stationary to the east of the Rocky Mountains. The circulation around this high pressure area is clockwise in direction. The bottom of the high pressure area sit over Texas and Mexico. Winds now sweep across the Gulf of Mexico and the Gulf of California to the west. Now following the clockwise circulation this moist flow of air is now pointed northeastward across the Desert Southwest and into the southern and central Rockies. As this moist air in forced upward clouds and rain are the result. Many times during this period we see thunderstorms form to the southwest and then move out over the plains bringing much needed moisture.
During the past 6 years of drought this high pressure area set up too far to the west and actually blocked moisture from coming up from the south. It now appears that we are back to a more normal pattern and as a result we should see more rain this year from this seasonal weather pattern.
One other factor to consider with this moist flow is that typically hurricanes from off the coast of Mexico and make their way north along the Baja. Every once in a while one of these hurricane will get sucked into the monsoonal flow and all that moisture is transported into the southern and central Rockies. This can result and very heavy rains for large areas of the Desert Southwest and the Rockies.
So the next time you hear the word monsoon don’t automatically think of the tropics, we have our own monsoon right here in Colorado.
In many portions of Colorado, July 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 August 2004 time period. As can be seen, above normal temperatures are expected for all of Colorado for August.
The map below shows forecasted precipitation deviances for August 2004. Normal or near normal precipitation is expected for August 2004 all of Colorado.
As can be seen in the below map, drought conditions are expected to continue to persist across the western 1/3 of the state, though improvement is noted in the eastern 2/3s of Colorado through October..
July started off rather slowly with very little precipitation to speak about. By the 15th of the month only 0.11 inch had been collected. Then on the 16th, a near record 24 hour amount of precipitation totaled 1.36 inches missing the 24 hour record for July 16th by only 0.02 inch. It should be noted that portions of the metro area especially the east metro area picked up over 2 inches of rainfall from the same storm. The remaining 16 days of the month had 7 days of measurable rainfall. The month finished with 2.52 inches and 0.36 inch above normal. This marked the second month in a row with above normal precipitation. There were 17 days with thunderstorms at DIA 6 of which were dry storms with no precipitation recorded and 3 storms only dropped trace amounts.
There were no precipitation records set or tied during July and none of the storms at DIA were severe. Also no hail fell at DIA during the month. After having said that, it should be obvious that DIA does not represent the metro area very well as severe storms and hail did hit many part of the metro area during July.
July 2004 finished below normal in the temperature department. The last time July was below normal for temperature was July of 1995 with an average temperature 1.2 degrees below normal. July 2004 featured 18 days with below normal average temperatures with the leader being the 24th being 20 degrees below normal. The 24th set 2 records, the low temperature of 49 degrees set a new low record beating the 50 degree old record set in 1911. The high temperature on the 24th was only 58 degrees, a new low maximum easily beating the old record of 65 degrees set in 1880. Temperatures during the month ranged from a high of 99 down to a record setting 49 degrees. There were 11 90 degree or higher days compared to July 2003 which recorded 24 90 degree days. The average amount of 90 degree days is 15.
The weather pattern in August is similar to the rest of the summer months but severe weather decreases significantly and on the average, especially towards the end of the month, daily temperatures begin to decline. Skies are generally clear between midnight and noon, but during the afternoon showers and thunderstorms develop along the foothills during the early afternoon and then move eastward across the plains.
The occurrence of severe weather decreases considerably during August compared to the severe weather months of June and July. The typical air mass aloft over Denver is nearly as warm as earlier in the summer, however the air mass is usually a bit cooler near the surface. As a result the air mass as a whole is more stable and the thunderstorms less intense. Tornadoes and Large damaging hail are fairly rare, especially after the middle of August. Because of slow movement, the thunderstorms in August are more likely to produce heavy rain than large hail.
By late August, the days become noticeably shorter and an occasional cold front slips across Denver and brings a nip to the air, a reminder that summer is really winding down. However, August still brings in some hot days. In fact, the highest temperature ever recorded in Denver was recorded during the month of August. It hit 105 degrees on August 8th in 1878.
The National Weather Service 30 day outlook model indicates that temperature and precipitation for the Denver area will be at or slightly above normal for August of 2004.
Sunrise/Sunset (Denver area)