The Weather Wire
April 2010 Volume 17 Number 04
Avg High - 53.5
Avg Low - 28.5
Snow - 12.8"
Season Snow - 58.8"
Precipitation - 0.80"
Avg High - 60.9
Avg Low - 34.2
Avg Snow - 9.1"
Avg Precip - 1.93"
Why So Windy?
If you thought it has been windy recently, it has been! The spring months are often the windiest time of year for many locations in Colorado. The reason is simple, the change of seasons and the warming of the earth’s surface. Winters grip still hangs on to the north while spring is in full swing to our south. These warm and cold air masses duel it out over Colorado and result in large swings in temperature with very warm and dry days and periods of rainy/snowy weather with the first threat of severe storms. These air masses are moved by the wind and the winds are strongest in areas with the tightest temperature gradient, or where cold and warm temperatures are separated by little distance such as a front. This collision of warmer and colder air occurs often in the spring and results in numerous days during the months of March, April and early May being considered breezy or windy. April is actually Denver’s windiest month of the year on average. Below is a table that shows the average wind speed per month in Denver:
Notice how the windiest months are in the spring and the calmest months are in the fall. The reason for the weaker winds in the fall is because the surface is now cooling resulting in a more stable atmosphere. The rapid warming of the surface as compared to the slower warming atmosphere creates atmospheric instability. This instability is caused by warmer air near the surface being warmer than the air around it which then begins to lift the parcel of air upwards. If the warmer air rises with enough force, moisture and spin severe weather can develop which is why most of our tornadoes, large hail and strongest squall lines occur in the spring with more diurnal trends as we move into mid-summer.
I don’t want anyone to forget about the strong windstorms that can occur adjacent to the foothills during the months of November through January as these famous wind storms have produced wind gusts in excess of 100mph. This type of strong wind scenario is driven more by topography, stability and upper level winds and are confined to a smaller geographic region often not affecting areas east of I-25. The springtime winds affect a much larger area and can last for a much longer period of time but their peak gusts are typically confined to the 45-60mph range and are most likely from the south or southwest and occasionally from the west.
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 April 2010. As can be seen, normal temperatures are expected for much of the state, though the southwestern areas of the state are expected to have above normal temperatures.
The map below shows forecasted precipitation deviances for April 2010. Virtually all of Colorado is expected to have above normal precipitation for the month..
Little in the way of drought remains in Colorado.
March of 2010 did not disappoint in the snowfall department as there was some impressive monthly totals in the Denver area with 12.8" reported at DIA, but most areas of the city received between 15-30" of new snow for the month. Precipitation was below normal at DIA, but this area does not represent the city very well and there were much higher precipitation totals most areas. I cannot remember when we tied or broke a high temperature record this winter as it has been very cold for the most part but there was a record high of 82 on the 30th. Temperatures in general were very close to normal with a monthly mean of 41.0 degrees which is 1.4 degrees warmer than the average of 39.6. As far as Denver goes we don't need another snowflake to make this year above normal in the snowfall department so any additional snow will just add to the snow surplus. Most of the snow in March came in two storms one on the 19-20th and another on the 23-24th.
April is typically the month where our last meaningful snows occur with 3 storms on average during the month. Not surprising, but snow can fall heavily during this month and it is the 3rd snowiest month of the calendar year on average with 9.1". High temperatures begin to warm up dramatically with average highs right around 60 degrees. Average lows also warm significantly with 34.2 degrees, but the average last freeze/frost is not usually until the second or third week in May. If it has felt windy lately it is because it has been and April is typically the windiest month of the year. Almost any form of precipitation can occur during the month with rain, sleet, snow, hail, etc and there can even be some severe weather towards the end of the month. Thunderstorms usually make an appearance this month but only a couple of days on average. The weather pattern looks to be drying out for the short term and that will likely result in normal or slightly below normal snowfall for the month and average to above average temperatures.
Sunrise/Sunset (Jan - June Denver area)
Sept 2009 to Apr 2010