Mike's Weather Blog Archive: October 2010

7NEWS is proud to once again be the official media sponsor for SUPER SCIENCE SATURDAY, October 30, at NCAR's Mesa Lab in Boulder.

Super Science Saturday is an annual event hosted by the National Center for Atmospheric Research (NCAR) that is FREE and open to the public. The event combines science education with Halloween fun and is ideal for teachers, students, and families. The excitement begins at 10 AM and lasts until 4 PM.

Its purpose is to get kids interested in science so they may perform cool experiments like this father-son duo from Brooklyn who launched a weather balloon with an HD camera and GPS unit nearly 19 miles into the atmosphere and got amazing video of the dark sky of space.

This year’s theme is Science With A Blast. Throughout the day, NCAR’s “Science Wizards” will explore the principles of exciting science with live demonstrations and hands-on activities. The day also includes interactive fun with the Little Shop of Physics workshop from CSU, weather balloon launches, a cryogenics magic show, face painting, an inflatable two-lane bungee run, the Wild Okapi Marimba Band, and many other fun activities.

“Super Science Saturday is a firm favorite with kids, parents, and teachers in the Boulder-Denver area,” says Laura Allen, an education and outreach specialist from the University Corporation for Atmospheric Research (UCAR), which manages NCAR. “We hope to see lots of kids and families dressed in their Halloween costumes ready to experience the wonders of science.”

NCAR is the world's premiere research facility for weather and climate and many of the top NCAR scientists will be on hand to answer questions about our often wild and fast changing weather. Also included this year is the outdoor physics adventure featuring a climbing wall, kayak tank, and mountain bike course!

Food and drinks will be for sale in the NCAR cafeteria.

Bring along a new or gently used coat to donate to our COATS FOR COLORADO campaign!

NCAR's Mesa Laboratory is located at 1850 Table Mesa Drive in Boulder.

For more information, contact David Hosansky at 303-497-8611, or Laura Allen at 303-497-2408.

This will mark the fourteenth year of Super Science Saturday, the largest public event NCAR holds each year, attracting over 3,000 attendees.

The weather will be quite lovely over the next few days, but I am watching the possibility of our first snowfall coming early next week.

Warm and dry weather will be the rule through the weekend, but by Monday and Tuesday, a cold front will move in from the west and may bring rain Monday afternoon, mixing with or changing to snow by Tuesday morning. It should not be a big storm, but certainly a sign that we are getting into the latter half of October - a time when the weather can turn snowy in a hurry.

Here is a link to the average first snow dates for the Denver area. Denver Snow Stats

For more information on Halloween snow click here

The famous STANLEY HOTEL in Estes Park is often covered in snow by Halloween. The hotel is also in a contest to be named the Spookiest Place in the Nation. Click this link to cast your vote for the Stanley!

I have compiled a variety of information about snow and snowstorms; I hope that you will find it useful and interesting...

How big can snowflakes get?

Snowflakes are agglomerates of many snow crystals. Most snowflakes are less than one-half inch across. Under certain conditions, usually requiring near-freezing temperatures, light winds, and unstable, convective atmospheric conditions, much larger and irregular flakes close to two inches across in the longest dimension can form. No routine measure of snowflake dimensions are taken, so the exact answer is not known.

Why is snow white?

Visible sunlight is white. Most natural materials absorb some sunlight which gives them their color. Snow, however, reflects most of the sunlight. The complex structure of snow crystals results in countless tiny surfaces from which visible light is efficiently reflected. What little sunlight is absorbed by snow is absorbed uniformly over the wavelengths of visible light thus giving snow its white appearance.

What causes the blue color that sometimes appears in snow and ice?

Generally, snow and ice present us with a uniformly white face. This is because most all of the visible light striking the snow or ice surface is reflected back without any particular preference for a single color within the visible spectrum. The situation is different for that portion of the light which is not reflected but penetrates or is transmitted into the snow. As this light travels into the snow or ice, the ice grains scatter a large amount of light. If the light is to travel over any distance it must survive many such scattering events, that is, it must keep scattering and not be absorbed. The observer sees the light coming back from the near surface layers (mm to cm) after it has been scattered or bounced off other snow grains only a few times and it still appears white. However, the absorption is preferential. More red light is absorbed compared to blue. Not much more, but enough that over a considerable distance, say a meter or more, photons emerging from the snow layer tend to be made up of more blue light and red light. Typical examples are poking a hole in the snow and looking down into the hole to see blue light or the blue color associated with the depths of crevasses in glaciers. In each case the blue light is the product of a relatively long travel path through the snow or ice. So the spectral selection is related to absorption, and not reflection as is sometimes thought. In simplest of terms, think of the ice or snow layer as a filter. If it is only a centimeter thick, all the light makes it through, but if it is a meter thick, mostly blue light makes it through.

Is it ever too cold to snow?

No, it can snow even at incredibly cold temperatures as long as there is some source of moisture and some way to lift or cool the air. It is true, however, that most heavy snowfalls occur with relatively warm air temperatures near the ground - typically 15F or warmer since air can hold more water vapor at warmer temperatures.

More About Blue Snow and Ice...

It is a common misconception that the blue color exhibited by glaciers, old sea ice, or even holes poked into a snow bank is due to the same phenomenon that makes the sky blue-light scattering. But nature has more than one recipe for producing the color blue. In frozen water and in the sky the processes are almost the reverse of each other.

A blue sky results when light bounces off molecules and small dust particles in the atmosphere. Because blue light scatters more than red does, the sky looks blue except in the direction of the sun (particularly when the sun is near the horizon and the blue light is scattered out of the sunlight, leaving the red color of sunrises and sunsets).

When light passes through ice, however, the red light is absorbed while the blue is transmitted. Were the operating process scattering as in the atmosphere, then the transmitted light would be red, not blue. However, because of the large size of snow grains and ice crystals, all wavelengths of visible light are scattered equally. Scattering therefore does not play an appreciable role in determining the color of the transmitted light.

It takes an appreciable thickness of pure ice to absorb enough red light so that only the blue is transmitted. You can see the effect in snow at fairly shallow depths because the light is bounced around repeatedly between ice grains, losing a little red at each bounce. You can even see a gradation of color within a hole poked in clean, deep snow. Near the opening, the transmitted light will be yellowish. As the depth increases, the color will pass through yellowish-green, greenish-blue and finally vivid blue. If the hole is deep enough, the color and light disappear completely when all the light is absorbed.

The color of ice can be used to estimate its strength and even how long it has been frozen. Arctic Ocean ice is white during its first year because it is full of bubbles. Light will travel only a short distance before it is scattered by the bubbles and reflected back out. As a result, little absorption occurs, and the light leaves with the same color it had when it went in.

During the summer, the ice surface melts and new overlying ice layers compress the remaining air bubbles. Now, any light that enters travels a longer distance within the ice before it emerges. This gives red end of the spectrum space enough to be absorbed, and the light returned at the surface is blue.

Arctic explorers and mountain climbers know that old, blue ice with fewer bubbles is safer and stronger than white ice. An added bonus for explorers is knowing that floating camps built on blue ice will last longer.

The storm during the week of March 17th, 2003 was one of the biggest in Denver history, but still came up short of setting the all-time record for the city for a single storm. That title is still held by an amazing storm back in December, 1913. That system was similar to this past storm (a slow moving low over southeastern Colorado, but it stalled for an extra 24 hours and as such, dumped even more snow on Denver and the Front Range. Denver tallied 46 inches from that storm system, while Georgetown had about 80 inches of snow!

Here is some information about winter weather and the storms that can affect Colorado. I hope that you find it interesting!

Of all the seasons of the year, winter is the one that most people around the country would identify with Colorado. Our high elevation means that it is winter for most of the year on our mountain peaks, with the snow-free time lasting only a few weeks.

The winter season often begins well ahead of the calendar, as the first snows in Denver often come as early as mid-September. Newscasts from around the nation show us digging out of the deep drifts well before Halloween. Yet the big secret that we keep is that we are not left snowbound for months by these big storms. Instead, the rest of the country stops paying attention to us while the snow quickly melts, and we are out playing golf again by the end of the week!

Colorado serves as a breeding ground for some of the most powerful storm systems that bomb the rest of the central and eastern United States with heavy snow. Low pressure storm systems frequently develop just to the east or to the "lee" of the Rockies. Strong winds aloft at the jet stream level (about 25,000 to 30,000 feet) squeeze over the mountain peaks and then out over the plains. As the air moves out away from the mountains, the pressure falls, creating a low pressure area. If conditions are right, this low will begin to swirl moisture into the region from the Gulf of Mexico. This moisture spins into clouds, rain and snow, and before long, a storm is born. These storm systems first dump heavy snow over eastern Colorado and then churn toward the northeast. Heavy, wet snow, sleet, freezing rain and even thunderstorms mark the path of these storms as they roll on toward the Great Lakes. The soggy systems that spin out of eastern Colorado can give a false impression to the rest of the nation. Those eastern storms often dump heavy snow on Denver, Colorado Springs, Limon or other cities on the plains, but leave the mountains with a much smaller accumulation. Television weather reports in other cities show the snow in Denver and the folks in those cities think, "Wow, if Denver got a foot of snow, the mountains must have really been hammered!" In fact, eastern storms tend to be blocked off by the mountains of the Front Range, and the ski areas may have only scattered clouds while Denver gets the big snow. This was the case back in October 1984, when the Broncos played the Packers in a blizzard at Mile High Stadium. The national television audience saw all that snow in Denver and inundated the ski resorts with calls for reservations. Being good businesspeople, ski resort personnel didn't mention the fact that at the time, skies were clear in Vail and Aspen!

An old saying about Colorado weather is very helpful when trying to figure out if a storm system will bring heavy snow. Remember - Pacific front, mountains bear the brunt; southeast low, Denver gets the snow. As I mentioned earlier, storm systems on the eastern plains spin their heavy snow over the Front Range and adjacent plains, but may miss the mountains. In contrast, a moist storm front from the Pacific Coast may dump very heavy snow on the mountains, but have very little moisture remaining by the time the storm slips down into Denver. Those Pacific fronts have a rough time staying intact as they first hit the Cascades and Sierra Nevada Mountains, then have to cross the Wasatch Range in Utah and finally struggle over the Continental Divide. When the once mighty storm finally tops the last of three or four mountain ranges, moisture is so depleted that Denver doesn't even get a flake of snow! Sometimes these storms regenerate into a major system again once they get farther to the east of Colorado. The leftover circulation of the storm will start to tap into the rich supply of moisture available from the Gulf of Mexico and the storm will once again become a powerful precipitation producer! Our neighbors in Oklahoma, Kansas, Nebraska and points farther east get a messy winter storm - but Denver and adjacent cities in the I-25 corridor have just some clouds and gusty north winds on the backside of the storm. These storms are frustrating to forecast as they usually feature headline making weather from the West Coast, with huge waves, heavy rain, wind and mountain snow. The storm takes a couple of days to get here, so there is plenty of build up and anticipation. First our mountains get heavy snow, but then the storm seems to jump right over Denver, before bringing nasty winter weather to extreme eastern Colorado and most of the Midwest. Such a storm scenario makes it seem like Denver has a big clear plastic dome over us!

The recent weathercasts were filled with the term "blizzard", which is a derivative of the German word for lightning. Early European settlers on the high plains were astounded by the lightning-fast changes in the weather, especially when a powerful cold front roared through.

The true definition of a blizzard has more to do with wind and visibility than with snow - a storm earns blizzard status when winds of thirty-five miles per hour or higher are accompanied by falling or blowing snow that drops visibility to a quarter mile or less. The sky above can be clear, but blowing snow at ground level can produce blizzard conditions. A severe blizzard is bad - winds over fifty miles per hour with visibility near zero due to blowing or falling snow. Certainly our pioneer ancestors saw some very scary winter storms, but even today strong winter storms can bring peril to travelers. The wide-open eastern plains of Colorado offer no resistance to the wind and can allow howling storms to swirl snow into drifts five to ten feet high during the worst blizzards.

The passage of a strong Canadian cold front is a major weather story on the eastern plains, but often not for the mountains. The wall of granite to the west of Denver serves as a pretty good barrier for the cold, dense air. Quite literally, the cold air is just too heavy to climb up and over the mountains. Many times a surge of Arctic air will blanket the eastern plains of the state and put us in the deep freeze, while in the mountains, temperatures stay much milder as the cold front stalls in the foothills west of Denver.

At 7News, we are always glad when you choose to watch the quality shows on ABC! I must stray just a bit from that recommendation to remind you that Storm Chasers will be returning to the Discovery Channel this Wednesday evening.

One of the featured tornado chasers is our very own Tony Laubach! Tony is the weather producer here at 7News, at least during the "off season" for severe thunderstorms and tornadoes. This past spring and summer, Tony was chasing with the TWISTEX research team, headed by veteran storm chaser Tim Samaras. Tim and Tony are both local scientists and have been on the trail of severe storms for many years.

Tim developed a special tornado probe called the HITPR - an acronym for Hardened In Situ Tornado Pressure Recorder. Tim has deployed these probes in the path of tornadoes for the last several years and has even equipped these probes with cameras to get a look inside of a tornado!

You can learn more about Tim Samaras and his tornado probes in my book THE COLORADO WEATHER ALMANAC.

Tim and Tony have been chasing storms recently to not only deploy the HITPR probes, but also to take amazing images of lightning with ultra high speed cameras.

To read more about Tony, check out his TornadoesKick website.

Follow along with Tim Samaras on his ThunderChase website.

Here is a link to the Discovery Channel promo for

Storm Chasers.

So, here is the plan, be sure to set the DVR for Storm Chasers, watch your favorite shows on ABC and by sure to stay tuned for 7News!

September ended as it began, warm and dry. In fact, September 2010 will go down in the record books as the fifth warmest and driest since 1870. Temperatures averaged nearly 4.5 degrees above normal and only .06" of rain was recorded.

The long range forecast for the upcoming fall looks like our present trend may linger, with fairly mild and dry weather expected.

The southwestern U.S. is expected to have a warm fall. This will be especially true from southern California through Arizona, New Mexico and west Texas. Later in the fall and early winter, storminess should sweep in from the Pacific and bring more precipitation from Washington across Idaho and Utah. Colorado will be on the southern edge of this storm track, but hopefully close enough to get some of the moisture from these southern storms.

In Colorado, our autumn weather outlook calls for temperatures to be warmer than normal, with a few cold surges, but nothing that last too long. We will be on the fringe of the storms that come into the northwestern U.S. and will catch some of the light to moderate rain or snow associated with the passage of these systems.

Precipitation will not be heavy as fall is typically one of the quieter times of year (for the most part). The upper level flow pattern should be primarily from the northwest to the southeast, bringing snows back to our northern mountains, while the southern and central areas may not see much in time to give our ski season a really good start. At lower elevations, we will get a few fast moving storms as the season grows deeper. We may have a little less snowfall than in the past year, as the northern storms drop most of their moisture over the mountains and are fairly spent by the time they reach the eastern plains.

For a graphic depiction of the long range outlook for the nation, check out these links to the Climate Prediction Center -

El Nino & La Nina

Denver National Weather Service

Colorado Climate Center

Climate Prediction Center

Autumn is an enigma in Colorado. One of the most pleasant and certainly most beautiful times of year, it's also a time when the weather can't seem to make up its mind. Summer is over and winter hasn't begun, but we still see a little of both. Thunderstorms still occur in September, but so does snow. October offers some of the most pleasant weather of the entire year, but you'd better have the snow blower ready to go just in case! By November, it can feel like January if subzero air settles in after a big, early snow. Autumn, of all the seasons, seems to have the biggest identity crisis.

As the days grow shorter, we see the end of the thunderstorm season. The lack of intense daytime heating doesn't allow for the strong convective lifting that helps to brew up afternoon storms. Additionally, the mid and upper levels of the atmosphere are comparatively warm after the long summer, so the air is relatively stable. Although the official end of summer is not until the third week of September, the psychological end of summer is Labor Day weekend. We begin to think less about thunderstorms and more about the first snow of the season.

Usually those early snows first occur in the high country. One morning a thin veil of fresh snow will suddenly show up on the high peaks and usually disappear by midday. Once in a while, an early snow will visit the Front Range cities. The earliest snowstorm on record for Denver was September 3, 1961, when four inches fell over the western suburbs of the city. Just a few years ago, on September 21, 1995, Denver was bombed by a record snowfall of nearly ten inches. This soggy, slushy preview of the upcoming season was very unwelcome - it damaged thousands of trees and power lines. The wet, heavy snow settled on trees still covered with leaves, and the overloaded branches crashed down on nearby wires. But even a major storm such as this does not last long in September. Within a day or so, the snow had disappeared under the steady gaze of the warm, early-fall sun. Golfers and gardeners were quickly back on the job under a brilliant blue sky.

By mid to late September, the jet stream winds are beginning to flex their muscles once again. The jet stream usually gets pretty quiet in late summer as the strongest winds aloft are found in central Canada in late July through August. In September, the increasing chill over the northern latitudes helps to force the jet stream farther south once more. As the winds aloft increase over the Rockies, the potential for stronger storm systems and major fluctuations in temperature increases as well. Cold fronts start to roil down from the north with more vigor, and the result can often be a gorgeous summer-like day with a few inches of snow coming right on its heels.

The average date for the first frost in Denver is October 7, with the first measurable snow on October 19. Most years stay snow-free in Denver through September, but October is a different story. In October the first significant low pressure storm systems of the season begin to form over Colorado. These storms bring easterly upslope winds along the Front Range and often the first opportunity for shovels and snow tires.

Autumn is not just a waiting period for the inevitable onslaught of winter. Every Coloradan looks forward to the delightful stretch of warm, sunny days known as "Indian Summer" - perhaps the nicest weather of the entire year. Brilliant blue skies, highs in the perfectly comfortable seventy-degree range, light breezes - in other words, ideal! Indian Summer is loosely defined as the warm, dry, quiet period of weather that follows the first killing frost. This weather pattern usually occurs during late September or the first two weeks of October, and is especially delightful because it coincides with the peak of the aspen leaves. There really is no meteorological significance to Indian Summer - it doesn't portend anything about the upcoming winter or reflect on the summer just past. Indian Summer is simply a time to try to slow down and savor the good fortune of living in Colorado!

It looks like we should see our peak color pretty much on schudule this year. The best color over the northern mountains should be from September 20th to the 30th. The central mountains will be about five days behind, with the southern mountain areas rounding out the last days of the month and the first ten days of October.

Perhaps the most appealing part of autumn is the gold found in the mountains each year. Not the gold sought by prospectors over a century ago, but rather the gilded glory of Colorado's famous aspen trees. The decrease in sunlight switches off the mechanism in the leaves that creates chlorophyll - the green color in the leaf. As the green fades, the gold color dominates until dying leaf flutters to the ground. The best years for aspen viewing are those with well-timed rains and no major fall storms. A too dry summer will send the leaves falling quickly, while a wet summer tends to make them darken to brown or black. The most brilliant display of aspen occurs when we have a mild late summer and periodic gentle rain, combined with a dry September that includes few big windstorms or early snows.

Usually the first signs of aspen gold begin in mid to late August over the higher forests of central and northern Colorado. By the second and third week of September, many aspen groves are well worth a day's drive. Usually the peak time to view aspen is around the last weekend of September. After that, early snows will knock down the leaves and others drop away by themselves. Aspen color does not vary nearly as much as the rich reds and purple leaves of the Midwest and East, but there is something about gold leaves against a backdrop of rich evergreen and deep blue sky that makes our fall mountains special indeed!

Nothing says "autumn" in Colorado quite like the sight of a mountainside covered in the stunning leafy gold of aspen trees. Colorado's famous high country aspen reliably turn gold from the second week of September through the first week of October. Populus tremuloides - or the quaking aspen - can be found in all eleven of Colorado's national forests and their autumn fireworks are worth the drive.

Aspen naturally propagate in areas where hardier trees have been damaged or destroyed. This was the case in Colorado, where the slender trees grew in after logging stripped trees from mountain areas. Characterized by their elaborate root systems, aspen reproduce by sending up suckers from the roots to create "clone" stands of trees. These clones, connected underground at the root, are genetically identical to the mother tree. The identical nature of a clone stand is most obvious in springs, when each tree in the stand leafs at the same time, and in fall, when each tree turns the same shade of gold.

Historically, native tribes used the aspen bark to make medicinal teas to alleviate fever. The inner bark was sometimes eaten raw in the spring, and the outer bark occasionally produces a powder that was used as a sunscreen. Aspen is a favorite of Colorado wildlife too. Beaver use aspen for food and building; elk, moose, and deer eat the twigs and foliage. Other names for quaking aspen are golden aspen, mountain aspen, popple, poplar and trembling poplar.

Despite Coloradans' affinity for aspen, these delicate trees are not highly recommended for residential landscaping, especially at lower elevations of the state. Aspen as susceptible to many diseases, their convoluted root systems often grow into sewage drainage systems, and they generally last no longer than about 10 years out of their native habitat.

Here is a good website, with info on the fall color...

www.parks.state.co.us.

Here are some great places to view the aspen gold!

1) Steamboat Springs, Elk River country north on County Road 129. Also check the view on Rabbit Ears Pass and Buffalo Pass east.

2) Colorado 14 through the Poudre Canyon west of Fort Collins

3) Trail Ridge Road (US 34) through Rocky Mountain National Park

4) Flat Tops country between Buford and Newcastle

5) Tennessee Pass, US 24, from Leadville to Vail

6) Boreas Pass between Como and Breckenridge, a 23 mile road cresting at 11,481 feet.

7) Guanella Pass between Georgetown and Grant

8) Grand Mesa, Colorado 65 east of Grand Junction and north of Delta.

9) Maroon Bells near Aspen, a classic Colorado view!

10) Independence Pass, Colorado 82 between Twins Lakes and Aspen.

11) Colorado 135 between Crested Butte and Gunnison. Also try Kebler Pass west of Crested Butte on Gunnison County Road 12!

12) Cottonwood Pass, Colorado 306 between Buena Vista and Taylor Park

13) Monarch Pass, US 50 from Salida to Gunnison.

14) Cochetopa Pass between Saguache and Gunnison.

15) Gold Camp Road - Colorado 67 between Divide and Cripple Creek.

16) Lizard Head Pass, Colorado 145 between Dolores and Telluride.

17) Slumgullion Pass, Colorado 149 between Lake City, Creede and South Fork.

18) US 160, Navajo Trail, between Pagosa Springs and Cortez.

19) Platoro Reservoir, south of Del Norte and west of Conejos.

20) Cucharas Pass, Colorado 12, from Trinidad to Walsenburg.

21) CO 103 from Evergreen Parkway west to Echo Lake.

22) McClure Pass - This is a spectacular 8,755 foot pass south of Carbondale along Colorado 133 and the Crystal River.

Information about our aspen leaves will help you plan your trip. It truly is a wonderful way to spend a day - when the aspens are in their full glory!