The Weather Wire
April 2005 Volume 13 Number 04
Avg High 52.9
Avg Low 25.9
Snow - 4.6"
Season Snow - 26.5"
Precipitation - 0.59"
Avg High 60.9
Avg Low 34.2
Avg Snow - 9.1"
Avg Precip - 1.93"
Spring time in Colorado usually means plenty of wet weather including heavy wet snows. Storms that develop during the months of March and April provide their own special challenges to weather forecasters.
As we progress through these two months the sun becomes progressively higher in the sky and average daily temperatures warm from the 30s to the 50s and 60s. Therefore one of the problems we have to deal with is the warmer temperatures in the ground and paved areas. This is a critical consideration for those who have the job of removing the snow. It is especially difficult for the weather forecaster as not only does he have to sift through the various models to forecast the right amount of snow for the storm, but for this time of year he has to take into account soil and pavement temperatures. He may be right in forecasting 4-6 inches of snow with 4-6 inches did falling, but be wrong in that none accumulated on paved areas and only 2 inches stuck to grassy areas.
Another factor that becomes a major player this time of year is elevation. During the mid winter months just about all areas are cold enough for snow and the higher elevations can get heavier snows depending on wind direction. Upslope flow favors the foothills to the west and the Palmer Divide to the south. For the spring months it becomes a matter of where the rain/snow line is. For example, the snows that hit eastern Colorado the first week in April was very elevation dependant. The rain/snow line was about 5800 feet, as a result the higher elevations in Douglas County received 4-6 inches of heavy wet snow, while the Denver metro area all below 5800 feet saw only rain and showers and no snow at all.
Another challenge for the weather forecaster this time of year is convective snows. With the warmer temperatures we see in the months of March and April comes the increasing likelihood of convective snows. If you think of the afternoon summer thunderstorm caused by heating you won’t be far off with convective snows. During the months of March and April with the warmer surface temperatures, as we get storms in from the west they bring colder air with them at the upper levels. Push this over a warmer layer of air at the surface and we create a very unstable air mass that is capable of producing snows with embedded areas of convective snows. These areas of convection can produce snowfall rates of 2-3 inches per hour over a short period of time. Much like forecasting summer thunderstorms we would be right in saying there will be thunderstorms today, but some areas will see the heavier rains and some lighter amounts and other none at all. We face the same difficulty with convective snows. Forecasting a storm to produce 2-4 inches of snow might be right for most areas, but for those spots hit by convective snows might see 3-6” or even more from the embedded heavier showers. Know exactly where those heavier embedded showers will hit is almost impossible to forecast ahead of time and the best that can be done is to track those areas when they appear on radar. This now become more of a nowcast type of forecast, much like we see in the summer months.
So spring here in the Rockies has more than its share of challenges for the weather forecaster.
Online Forecasts Available Again
Skyview Weather is happy to announce that online forecasts and snow reports are again available on our sister www.anythingweather.com website. Forecasts and snow reports are password protected, but an email to Tim@Skyview-WX.com requesting your forecast and/or snow reports be available online will result in an account being setup for you. As always, forecasts and snow reports are for client use only, but with the online access, forecasts and snow reports are just a click away from any computer with an internet connection!
Drought conditions continue to improve across most of Colorado, with normal to slightly above average precipitation during March 2005. Improvement continued through much of Colorado.
The map below shows forecasted temperature deviances for the April 2005 time period. As can be seen, normal to above temperatures are expected for much of Colorado for April.
The map below shows forecasted precipitation deviances for April 2005. Normal or near normal precipitation is expected for much of Colorado for April 2005.
As can be seen in the below map, most of the state has come out of the widespread drought conditions of a year ago, improvement will continue in Northwest and Northwest Colorado through June 2005.
March 2005 finished with below normal precipitation with a total of just 0.59 inches. This was 0.69 inch below the normal of 1.28 inches. This makes March the 6th month in a row with below normal moisture. Again we must remind you that in the areas were we get our water, in the high country, the snow pack is above normal. There were plenty of storms that moved through the state however and there were 10 days with measurable precipitation of which 3 days recorded greater than 0.10 inch. What is supposed to be Denver’s snowiest month with an average of 11.7 inches, March 2005 came in with only 4.6 inches at the old Stapleton site. Other areas around the metro area faired better; Highlands Ranch 13.5”, Boulder 10.1”, Golden 11.5”, Castle Rock 19.4” and Roxborough Park 18.3”.
Temperatures during the month finished near normal with an average reading of 39.4 degrees. This was 0.2 degree below the normal of 39.6 degrees. Temperatures during the month ranged from a high of 74 degrees down to a low of 14 degrees. No temperatures records were either tied or set for March of 2005.
Is a transitional month for most of the country and this is especially true for Denver. Almost any type of weather can occur and usually does. Tornadoes, thunderstorms, hail, snow and dust storm are all possible during the month. In addition, there are plenty of pleasant sunny days with temperatures ranging from the 60s to low 80s. On April 30th in 1992 the mercury climbed to the highest April temperature ever, 90 degrees.
In April, Denver is assaulted from all sides by varying types of air masses which accounts for the wide swings in the types of weather. Arctic air still occasionally invades the area and often teams up with an eastward moving Pacific storm producing snow in Denver. At other times, warm moist air from the Gulf of Mexico moves into the area and thunderstorms occur, sometimes occurring just before the snow. In addition, warm dry air from the Desert Southwest can bring warm temperatures and low humidity's to eastern Colorado.
The temperature range for April is from 90 degrees down to 2 degrees below zero. April is the third snowiest month of the year with an average of 8.9 inches and is the windiest month of the year with an average speed of 10 mph. For the month you can expect 2 thunderstorms to occur.
April 2001 was highlighted by a strong winter storm that produced blizzard like conditions that moved across the metro area on the 10th and 11th. The storm dumped 10.0 inches on former Stapleton. The storm produced plenty of heavy wet snow with southeast Aurora reporting 18 inches and 5 foot drifts, Parker reported 16 inches with 3 foot drifts, Westminster 9 inches and Littleton 8 inches. Even though a great deal of snow fell, by the 12th nearly all of the white stuff had melted away.
Sunrise/Sunset (Denver area)