November 3, 2009

Oct. 2009 ended as the second coldest month on record for the city of Denver, with an average temperature of 42.9 degrees. It was the fifth snowiest Oct. since records began with a total of 17.2 inches measured at Denver International Airport.

There were five record low temperatures either set or tied last month and one new record high was tied.

No thunderstorms were observed during the month and eight days had dense fog. We typically see one day during Oct. with dense fog.

Dense fog is defined as reducing the visibility to a quarter-mile or less.

The peak Oct. wind was 54 mph from the southwest on the fifth day.

October 26, 2009

Does it always snow in Denver on or around Halloween?

The answer is no, but it sure seems like it does -- and this year is no exception.

The Mile High City has less than a 20 percent chance of seeing a snowfall on Halloween, according to weather statistics since 1954.

In fact, there have only been 10 years during that time where snow fell on October 31.

However, that percentage jumps to 43 percent if we consider snow that was already on the ground or that fell after midnight.

And if we include the years with a cold, wet rain that mixed with snow over the higher elevations, or years with snow the week of Halloween, we well exceed 50 percent -- which might be why it seems like Denver almost always sees snow on Halloween.

The last time snow fell on Halloween day along the Front Range was in 2004. Rain started during rush-hour that year and quickly changed to snow by 8 pm. Some locations in the foothills saw over a foot accumulate.

The year with the biggest snowfall on Halloween was 1972 with 8 inches measured in Denver. The high that day was only 30 degrees.

October 13, 2009

Can you believe the high of 26 degrees and the low of 17 degrees this past Saturday? It seems too early for those type of temperatures.

The chilly weekend made me wonder if Denver could experience single-digit low temperatures this early in the season.

To find the answer, I dove into Denver's climate records and looked at all the record low temperatures for the city.

I found out we can experience single-digit temperatures in October, and the earliest occurrence happens to be on this date back in 1969.

In fact, it was the strongest early season winter-blast to hit the Denver area in recorded history, and the records still stand today.

On October 12, 1969, the temperature fell to 10 degrees behind an arctic cold front, establishing a record low for the date. The next night, October 13, 1969, the mercury fell to 3 degrees above zero, also setting a new record.

To this date, that is the earliest single digit low temperature on record for the city of Denver.

The chill remained into the day on October 14 with the morning starting out at 4 degrees and the high climbing to 36 degrees -- both new records for the date.

The Front Range was blanketed by snow during the cold blast. It was a true winter wonderland.

The cold and wet weather was not limited to the northern Rockies. In fact, much of the lower 48 states were under the influence of a winter-like pattern.

The cause was the jet stream. It had carved a large trough of low pressure over much of the lower 48 states.

On the backside of the trough, there was a large ridge of high pressure that pushed record heat all the way to Alaska. While Denver experienced a high of just 24 degrees on October 13, 1969 -- Fairbanks, Alaska set a record high of 65 degrees, which still stands today.

The unsettled weather pattern of October 1969 allowed the month to end as the wettest, coldest and snowiest October on record for Denver. Those records still stand today.

Click here for more October data for Denver.

Because October 1969 was so unusual for such a large part of the nation, there was a paper written about the cause and effects of the weather pattern. The paper is complete with maps and charts.

Click here to view the paper.

October 3, 2009

It's been wet across Denver and the Front Range this year, with over 15 inches of moisture measured at Denver International Airport since Jan. 1.

That is almost 3 inches ahead of where we should be on this date.

Because it has been so wet, last week's taste of fall weather has many wondering how much snow will fall this year.

Official long-range forecasts by the Climate Prediction Center show October-December have equal chances to be either drier or wetter-than-normal.

But Denver's past weather may hold a different answer, depending on how you look at it.

Since 1949, there have been 20 years that were much like 2009, with Denver exceeding 15 inches of precipitation between January and September.

Of those years, 50 percent experienced wetter-than-normal conditions between October and December. That's good news if you're hoping for snow.

But since 1995, there have been seven years like 2009, and of those, 86 percent were drier-than-normal between October and December.

Don't be let down by the statistic above if you're a fan of the snow. The study of climatology looks at weather records usually spanning 30 years or longer.

So according to climatology, the forecast for a snowy autumn is like that of the Climate Prediction Center -- equal chances.

Denver Normals

Normal precipitation for Denver between October and December is 2.60 inches. Most of that falls in the form of snow with 23.5 inches on average.

Denver's average date for the first freeze is around Oct. 7, and first snow is around Oct. 15.

Plan Ahead

Residents along the Front Range of Colorado know that anything is possible when it comes to weather.

So don't break out the shovels just yet, but it might be a good idea to get prepared for winter as the calendar turns to October.