DENVER -- If you are like me, you were probably a bit surprised when you looked outside Sunday morning. Where did all this snow come from?!?

The meteorologists of 7NEWS talked about unsettled weather for the past week -- but the intensity was somewhat unexpected -- so why? What changed?

To put it in a nutshell, Storm No. 1 was a little slower to move away -- supplying us with more moisture than we anticipated -- allowing for the heavier snow totals.

Meanwhile, Storm No. 2 arrived about 12 hours ahead of schedule during the overnight hours on Saturday.

In meteorology, a small shift in the projected timing of two features, such as 6 to 12 hours, can really change a forecast.

Visual Explanation Of Current Weather

Click here for a map to follow along with the description below. The map shows the upper-level wind pattern over the United States at 6 a.m. Sunday morning.

Colorado is sitting between two areas of low pressure and they are working together to put the squeeze on the state.

First locate Storm No. 1, or the area of low pressure over extreme northeast Kansas -- which is evident by the circle near Kansas City, near the center of the map.

Notice how large the circulation is around the low pressure -- you can see this by following the black lines of constant pressure (isobars) and the green moisture plume that flows around it. It stretches from Texas and Louisiana to Chicago and Minneapolis, then back into northeast Colorado.

The pattern, or circulation, shows the wind field around this low pressure. The circulation around a low pressure is counter-clockwise in the northern hemisphere.

Now notice Storm No. 2 -- the area of low pressure sitting to the west of Colorado, noted by the large, open circle over Utah. It almost looks like a horseshoe sitting on it's side.

This low pressure is diving south out of Canada -- or "digging" as we like to say in meteorology -- and putting Colorado in a favorable area for lifting the atmosphere. In other words, the air over Colorado is rising up.

So the low pressure to the east of Colorado was pumping in moisture while the one to our west was lifting the air. These two processes are working together to squeeze out that moisture in the form of snow.

Where does the wind come from?

The final piece to the puzzle is a very strong jet stream -- or winds in the upper atmosphere passing over Colorado. At the jet stream level -- located 20,000 to 30,000 feet above the ground -- wind speeds are 120 to 150 mph.

This wind energy mixes down to the surface, and when combined with snow -- results in heavy blowing and drifting.

Blizzard conditions have been reported across much of northeast Colorado, including along Interstate 70 near Limon, where wind gusts were as strong as a tropical storm late Sunday morning.

Will this last into Monday?

This will not be a prolonged storm system. As the low pressure to the east of Colorado continues moving away, it will take much of the moisture supply with it.

Snow will decrease in intensity as we head into the evening hours on Sunday. Some light snow showers or flurries may linger into early Monday morning, especially south and east of Denver.

Even with the snow ending, the Monday morning drive will still be slow and slick in spots, especially on side streets.

You can count on 7NEWS for the latest weather and traffic starting at 5 a.m. Monday.