The Weather Wire
April 2009 Volume 17 Number 04
Avg High - 56.6
Avg Low - 27.0
Snow - 13.8"
Season Snow - 30.7"
Precipitation - 0.83"
Avg High - 60.9
Avg Low - 34.2
Avg Snow - 9.1"
Avg Precip - 1.93"
New Severe Thunderstorm Warning Definition
Becoming effective this summer is a new definition of a Severe Thunderstorm. Below is the previous definition:
Severe Thunderstorm: A thunderstorm which produces tornadoes, hail 0.75" or more in diameter, or winds of 58mph or more (50kts).
The NEW Severe Thunderstorm definition:
Severe Thunderstorm: A thunderstorm which produces tornadoes, hail 1.0" or more in diameter, or winds of 58mph or more (50kts).
Obviously the only change is the size of the hail so how will this impact us here in Colorado? Well, most of our thunderstorms here in Colorado become "severe" by definition strictly by the size of hail alone as we receive more hail here along the Front Range than any other populated area in America. The second most common reason for severe thunderstorm warning is winds and third, tornadoes. Since hail is the most common reason for NWS issuing Severe Thunderstorm Warnings here in Colorado there will likely be less warnings issued on a daily basis. This is good in the sense that in theory there will be less watches and warnings issued and the ones that do get issued will be taken more seriously. We will see how this goes as old habits are hard to break and in the past some warnings have been issued on borderline storms even with the 0.75" criteria. With less watches and warnings there should be less confusion on exactly where the most severe weather is occurring.
Some of the downfalls of this definition change is that there can be damage done with storms below severe criteria. Minor hail damage can occur with hail less than 1.0" in diameter and is typically minor damage, but damage none the less. Combine winds of less than 50mph with hail less than 1.0" in diameter and wind blown hail can cause even greater damage, although typically to one side of the object. Overall I believe this warning change will help eliminate the borderline issued warnings in the past and allow the strongest storms with the greatest threat to life and property to be brought to the forefront.
Areas of drought have spread across much of eastern Colorado as well as northwest Colorado as a result of our precipitation deficit year to date.
The map below shows forecasted temperature deviances for April 2009. As can be seen, it is expected that all of Colorado to have above normal temperatures for the month of April 2009.
The map below shows forecasted precipitation deviances for April 2009. Normal precipitation is anticipated for all of Colorado March 2009.
Some improvement in drought conditions is expected along the Front Range of Colorado during the April to June time period.
March of 2009 was a continuation of the warm and dry weather from February until the last week of the month. The average high was 56.6 degrees and the average low was 27 degrees, both were above normal resulting in a monthly mean of 41.8 degrees which is 2.2 degrees above normal. Up until the blizzard on the 26th there was only 0.12" of precipitation for the entire month. Thankfully the last week of March brought much needed snow and precipitation. Snowfall for the month ended up at 13.8" which is above normal, but the water content was low resulting in a monthly deficit of nearly half an inch. The month was rather windy with an average speed of 11.6mph and two days with gusts of 50mph or more reported at DIA. Don't let the above normal snowfall for the month of March fool you as we are continuing to fall further into drought along the Front Range.
April is normally our transition month coming out of winter into Spring with a wide variety of weather ranging from downright hot to freezing cold with thunderstorms or even a blizzard. The average highs are now in the 60s and the average low for the month is just above freezing. April is the 3rd snowiest month of the year, averaging 9.1", but snow typically does not stay on the ground for long. As far as total precipitation goes, 1.93" is normal, but even with the active weather so far this month up to the 9th there is only 0.06" so far at DIA. Storms are moving through, but the position of these storm systems are favoring surrounding areas and not the Front Range in particular. This trend will likely continue resulting in April of 2009 ending up below normal in both precipitation and snowfall. Temperatures however may actually be below normal due to the active storm track bringing increased cloud cover and cooler air.
Sunrise/Sunset (Jul - December Denver area)
October 2008 to April 2009