Weather Resources - FAQs

We get many e-mails and phone calls from viewers with similar weather related questions. Below are the answers to some of the most common questions we receive. If you have a question that is not answered below, please e-mail us.

Why is the official temperature for Denver recorded at Denver International Airport (DIA)?

Denver’s official temperature along with all other weather information including snowfall is recorded at DIA because commercial airports are the origin of regular weather observations in the United States. This is mandated by the National Weather Service and the Federal Aviation Administration. 
The official weather observation location has actually been moved multiple times since 1871 resulting in an incongruous climate history for Denver. Weather observations were originally recorded downtown, first near the corner of Larimer & 16th Streets and then at the Post Office building at 19th & Stout Streets. In 1950 the official observation station was relocated to Stapleton Airport before being moved to DIA in 1995.
9NEWS is not involved in the process of determining the location of official weather observation stations.

Where, when, and how is snow measured for Denver?

The only official snowfall measurement for the Denver area is recorded at DIA on the southeast side of the airport. This measurement is recorded daily at midnight using an automated system. All other snowfall measurements around the metro area are considered "unofficial". Until 2008, the official snow measurement for Denver was recorded at the former Stapleton Airport site.

Where can I find historical weather data?

The climate section on the Denver National Weather Service website offers historical weather data for Denver going back five years. Click here and then click on “Preliminary Climatology Data (CF6)” to find daily information about temperature, precipitation, snowfall, wind speed, etc.

For historical weather data beyond five years ago or for locations other then Denver, visit the National Climatic Data Center website or call them at (828) 271-4800. The NCDC may charge a fee for their data.

For detailed precipitation records for hundreds of locations throughout Colorado, visit the Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) website.

You may also be able to obtain information from the Colorado Climate Center at Colorado State University in Fort Collins.

How many sunny days does Denver really get?

Many Chamber of Commerce publications from all regions of the state boast 300 days of sunshine each year in Colorado. The problem is there is no official definition of a “day of sunshine”. But let’s presume any day with less than 30% of the sky covered with clouds is “clear”, any day with 80% or more of the sky covered with clouds is “cloudy”, and any sky cover in the middle is “partly cloudy”. Using this definition, each year Denver averages 115 mostly clear days, 130 partly cloudy days, and 120 cloudy days. The claim of 300 days of sunshine each year is only accurate if every day with at least a peek of sunshine is considered a “sunny” day. There are relatively few totally clear days in Colorado and therefore the claim could be considered misleading.

What is wind chill and how is it calculated?

Heat produced by the human body radiates out of our skin and into the surrounding air. When there is no wind, this thin layer of heat partially insulates us from the full effect of the cold surrounding us. When conditions are windy, this layer of heat is swept away from the body and thus the full impact of the cold air is felt on our skin. Even though the actual air temperature is the same when conditions are windy, it "feels" colder. The wind chill temperature gives a comparison to what it would feel like at a lower temperature if there were no wind. Wind chill only applies humans and other living things; it has no effect on objects such as vehicles. Click here for more information.

Who activates the tornado siren in my town?

9NEWS does not have direct control over any tornado or severe weather sirens. They are typically activated by city or county officials, usually a police or fire department or emergency management personnel. Some officials wait for the National Weather Service to issue a tornado warning, while others wait until a tornado has been identified by spotters.

What weather related educational materials do you have advailable for teachers and students?

Our partners at the USA TODAY have developed a website with links to a wide variety of weather related material especially for teachers. Click here.

NOAA and the National Weather Service have also published a comprehensive website to help students, teachers, librarians and the general public access resouces for learning about the enviorment. Click here.

What is high pressure and what does it mean for Colorado weather?

When the atmospheric pressure is above 1013.25 millibars (the equivalent of 29.92 inches of mercury), we are considered to be under high pressure. This implies that the atmosphere is "denser" and therefore air tends to sink. Winds flow in a clockwise motion around the center of high pressure. Sinking air under an area of high pressure generally means a lack of cloud cover, precipitation, and wind. During the summer months, temperatures are usually very warm with high pressure while the opposite is true in the winter.

What is low pressure and what does it mean for Colorado weather?

When the atmospheric pressure is below 1013.25 millibars (the equivalent of 29.92 inches of mercury), an area is considered to be under low pressure. This implies that the atmosphere is "less dense" and therefore air tends to rise. Winds flow in a counter-clockwise motion around the center of low pressure. Since the air is rising under an area of low pressure, it cools and condenses generally causing clouds and possibly precipitation.

What does “radiational cooling” mean?

When skies are clear and winds are light or calm, the heat accumulated during the day rapidly rises, or radiates upwards. This results in a quick drop in temperatures shortly after sunset.

What is the difference between “partly cloudy” and “partly sunny”?

They essentially mean the same thing.  “Partly cloudy” can be used during the day or night, while “partly sunny” obviously is only used during daylight hours. They are both supposed to represent sky conditions where between 32% and 69% of the sky is predominately covered by clouds. This is more of a generalization for the time period in question, and does not mean that skies couldn’t be nearly clear or totally cloudy for brief periods.

What is the difference between “isolated” and “scattered” precipitation?

Forecasts on 9NEWS will often include both of these terms. Scattered is a more common occurrence than isolated. In other words, you are more likely to see rain or snow when there is a chance of "scattered showers" than when there is a chance of "isolated showers".

What is a “Chinook” wind and why does it bring warmer temperatures to Denver?

A “Chinook” or “downsloping” wind refers to a westerly wind that descends the leeward side of a mountain range. As Chinook winds force an air mass down the east slope of the Front Range Mountains, the air mass encounters stronger atmospheric pressure causing it to warm. This generally results in gusty winds causing warm, dry conditions for the Denver area. Chinook winds where named after the Chinook Indians who lived along the eastern slopes of the Cascade Mountain Range in present day Oregon and Washington where these dry downsloping winds also occur. Chinook winds occur all along the Front Range of the Rocky Mountains from Alberta, Canada to Albuquerque, New Mexico.

What do you mean by “upslope” and why does it bring precipitation to Denver?

9NEWS Meteorologists will often use the term “upslope” during weathercasts as an easy way to refer to “orographic lift”. This lifting occurs when air is forced from a low elevation to a higher elevation as it moves over rising terrain. This occurs frequently in Colorado when an easterly wind is present over the Eastern Plains. As the air moves west it encounters the mountains and is forced upward. As the air gains altitude, it expands and cools. Cold air can’t hold moisture as well as warm air and therefore moisture contained within the air is forced out through a process called “condensation” which changes invisible water vapor into a liquid. As the air condenses, it creates clouds and often precipitation. The process can bring significant snow to Denver in the winter and heavy rain in the summer.

Where can I find information about pursuing a career in Meteorology?

We recommend you use the Career Guide published by the American Meteorological Society. A list of colleges and universities that offer courses in meteorology, atmospheric science and weather forecasting can be also found here.

What does it take for a winter storm to be declared a "blizzard"?

The definition of a blizzard varies from one region to another based on the severity of the weather season in that region. In Colorado, the National Weather Service has established a criterion for determining if a winter storm is severe enough to be considered a blizzard. For  lower elevations including Denver, a storm must produce the following conditions; sustained  winds of at least 35 mph, considerable falling and drifting snow, visibility of less than ¼ mile, a and storm duration of at least 3 hours. The same criteria in used for the foothills and mountain expect winds much reach at least 50 mph in the high country for a storm to be labeled a blizzard.

What are El Niño and La Niña and how do they affect Colorado?

El Niño and La Niña are part of a climate pattern called ENSO (El Niño Southern Oscillation) that occurs across the tropical Pacific Ocean on average every five years. El Niño is characterized by above average temperatures in the Pacific while La Niña refers to below average temperatures. In Colorado, El Nino years tend be wetter than average. The summer monsoon is strengthened bringing more afternoon thunderstorms and in the winter, El Nino tends to bring above average snowfall to the southwest and central mountains but Denver and the Front Range can see below average snowfall. The effects of La Nina can vary widely across Colorado but typically drier conditions are observed during La Niña years.

Where can I download the 9NEWS desktop weather icon?

The software required to run the desktop weather application is no longer available.