DENVER -- Wednesday December 3, 2008

The fast paced weather pattern that has kept Colorado on a meteorological roller coaster will bring a dose of cold and snow today. After an unseasonaly warm Tuesday with highs near 70 degrees, a strong cold front has blown through the state, bringing a 35-40 degree drop in temperatures and another round of light snow. The snow will gently fall off and on through Thursday in the metro area and may total up to 2-4 inches before it ends. Northern extremes of the state could see double that total, while the mountains around Steamboat may end up with nearly a foot of snow.

The brunt of this storm system will affect the northern half of Colorado, while the south and southwest parts of the state will miss the majority of the cold and snow. If you are planning to travel during the next 24 hours, the worst driving conditions should be on I-80 in Wyoming, I-76 into Nebraska and I-25 north of Denver. Interstate 70 will have icy and snow covered areas from west of Evergreen to about Gypsum. Highway 40 will be snowpacked and slick over Berthoud and Rabbit Ears.

The storm will exit the state early Friday, with clearing skies and milder weather for the weekend. The next cold front will arrive Monday, with a chance for more snow in the mountains. Right now, it does not look as though it will be a major storm.

Monday December 1, 2008

If you're a sky watcher, you'll love the scene in the southwestern sky! The planets of Jupiter and Venus are visible along side the crescent moon. The best viewing will be about an hour after sunset and looking southwest. Try to get away form the city lights and you'll have a much better view of scenic nighttime sky.

Meanwhile, areas of Colorado are recovering from the surprise snowstorm that rolled through over the weekend! Predictions for the weekend were generally much lighter than what we actually saw. What happened was something called "convective symmetric instability", or CSI. What happens is a summertime-like instability profile sets up creating a thunderstorm-like environment. When this happens during the winter, we typically see bands of very heavy snow form in areas as isolated as those in a summertime thunderstorm pattern. When combined with the weak upslope that was suppose to lead to the lighter accumulations we called for, this CSI element adds two or three times that amount. Unfortunately such events are not seen in the models, and in this case, there was not any real instability forecasted, thus we had no real advanced warning on such an event. That lead to the lighter than reality predictions we saw, and thus fooled most of us in the weather-forecasting arena from the National Weather Service all the way over to us here in the 24/7 Weather Center. While its no excuse, I hope this helps explain a bit about what happened over the weekend!

Tuesday November 25, 2008

If you're hunting for great gift ideas for the weather nut in your family, here are a couple of great suggestions.

The Colorado Weather Almanac, all the info you need on Colorado's weather! Contains tons of color photos and tons of great facts on the weather unique to Colorado!

The 2009 Weather Calender, I am featured in the 2009 calender along with amazing photographs from the world's top weather photographers!

Both items are available through our website and make great gifts for the weather nut in your family!

Thanksgiving has a change in the weather in store with cooler temperatures and maybe some light snow in the mountains a few flurries at lower elevations. Definitely not a major storm. Mild conditions return early in the weekend ahead of the next storm expected in on Sunday. Again, just a change in temperatures with light snow possible. Still nothing big on the horizon as temperatures will return to the 50s for next week with the quiet weather pattern hanging around.

Sunday November 23, 2008

If you're going to be traveling over the Thanksgiving Holiday, find out what kind of weather to expect on your way with the 24/7 Weather Interns! We will be manning the phones on Monday and Tuesday from 4:00 - 7:00 p.m. Give us a call and we'll give you the expected weather along your route of travel, or for your flight destination. On Monday you can speak with the weather interns from the University of Northern Colorado, and on Tuesday our interns from Metro State College will be on the phone banks. We are expecting some interesting weather across parts of the nation over the holiday weekend, so be prepared by calling our special number: 303.832.2557.

Bring Your Family To NOAA on Tuesday November 25th

If you're looking for something fun and educational to do with your kids this week, bring them up to NOAA's David Skaggs Research Center in Boulder on Tuesday. This year marks the 10th anniversary of the center, and Tuesday's event will feature demonstrations and exhibits covering NOAA's quest to understand our environment.

NOAA, (National Oceanic And Atmospheric Administration), studies our environment, from the surface of the sun to the bottom of the world in Antarctica, and from remote corners of the planet where air samples are taken to their lab in Boulder where samples are analyzed. The climates of the past are captured in tree rings and ice cores, and the climates of the future are predicted by computer models.

Some of the other activities on Tuesday will include a weather balloon launch at 1:00 p.m. Showings of NOAA's spectacular "Science On A Sphere", hourly briefings at the Space Weather Prediction Center, plus talks throughout the day on weather awareness and safety, Colorado's changing weather and a sneak preview of our upcoming winter weather.

This is a great opportunity to tour one of the premiere meteorology and climate research facilities in the nation.

When: Tuesday, Nov. 25, from 9:30 a.m. to 3:00 p.m.

Where: 325 Broadway, Boulder (west side, south of Baseline, turn at Rayleigh Avenue)

How: Visitors to NOAA, must stop at the visitor center just west of the main Department of Commerce entrance. Adults must show a current photo ID.

Contact: Carol Knight, 303-497-6401, or visit NOAA Boulder online.

Thursday November 20, 2008

After several days of 60s, 70s and nearly 80s, Mother Nature has turned a cold shoulder to eastern Colorado. A strong cold front slid into the state last night, pulling an icy mix of fog, flurries and freezing drizzle down from the northern plains. Under a slate gray sky, the weather will remain "stratus quo" through the afternoon, with chilly temperatures in the low to mid 30s and periods of very light drizzle or flurries. Road conditions were slick in places early today, and the foothills below 8,000 feet will likely stay that way this afternoon.

The cold air is dense and does not flow uphill very easily. The depth of this pool of cold air is only a few thousand feet thick, so higher elevations to the west will stay above the cold, cloudy conditions. Most of the mountain areas will be partly cloudy and much milder through the day. In general, the cold air will stay below elevations of 8,000 feet, with much milder weather above and to the west. Check out our LIVE cams on the weather navigation bar to see the difference from the plains to the mountains.

The cold air mass will ease off to the east starting tomorrow, with skies clearing and the temperatures moderating over the weekend. Saturday will be the pick day of the weekend, with highs returning to the upper 50s. We will not see a return to the 60s and 70s anytime soon, but the weather should be nice for Sunday and the early part of next week.

By the way, if you are planning to travel for Thanksgiving, let 7News be your "meteorological guide". Monday and Tuesday we will again host our HOLIDAY TRAVEL LINE from 4 pm to 7 pm each day. Meteorologists from Metro State College and the University of Northern Colorado will be taking your calls and providing FREE travel weather outlooks for anywhere you are planning to go. The number for the service will be posted on 7News, starting Monday at 4 pm.

Tuesday November 18, 2008

If you thought that the weather was unusually warm today, well, you're right.

Shortly before 3:00 p.m. the temperature at Denver International Airport reached 78 degrees.

The previous record is 74 degrees, which was recorded in 1995.

Keep in mind, the average high on this date is 50 degrees.

The average low is 22, and it feels like we are living on borrowed time with this warm weather.

The minimum temperature between midnight and noon was 47 degrees.

Assuming the temperature doesn't cool below 47 degrees before midnight, then today's low will set a record for a record high minimum.

Sunday November 16, 2008

It has been a dry autumn in Colorado, to say the least. Denver officially remains nearly five inches below normal on precipitation as of today. Since January 1, we've received 9.81 inches of liquid precipitation. Measuring precipitation, especially snowfall, can be very tricky. We will discuss that in more detail later in this blog. Keep in mind that official readings for Denver are taken by the National Weather Service at Denver International Airport. The varying terrain and elevation have a profound effect on precipitation totals in our area. Here is an example of how variable precipitation readings can be across the Front Range.

On Friday morning, Denver officially received 1/10 of an inch of snow, which amounted to 1/100 of an inch of liquid precipitation. According to the CoCoRaHS volunteer observation network, some areas just south of Denver received up to 3.6 inches of snow, with liquid totals of 0.17 inches. So, while Denver's official precipitation deficit can seem a bit alarming, some unofficial stations reported healthier snow totals. With Friday's storm in particular, the higher terrain south of Denver caused an area of enhanced snowfall, giving those places higher totals.

Gathering accurate snowfall measurements can be difficult, mainly due to the wind that sometimes accompanies snow events in Colorado. Volunteer observers in the CoCoRaHS Network are asked to walk around their yards with standardized measuring sticks and take readings in a number of places. Then, the totals are averaged. The tricky part comes in when attempting to get an accurate reading on the liquid equivalent of the snow that has fallen. Snow falls into the observer's rain gauge. However, the wind can affect the amount of snow that is caught by the gauge. That is why we take something called a "snow core measurement". That involves turning the rain gauge upside down, depressing it into the snow all the way to the ground, sliding a clip board or piece of cardboard under the gauge to capture the snow, then melting it down. This gives a more accurate reading of the liquid equivalent of the snow that is on the ground. It takes a bit longer, but snow cores can be very revealing.

All things considered, it really has been a dry fall so far across much of our state. But as we explained, the readings can be highly variable. Persistent high pressure ridges have been in place this year, preventing storms from dropping large amounts of snow on us. The snows we have received have been due to passing cold fronts, which traditionally move through very quickly and therefore have light snow totals associated with them. When Denver receives a "big" snow, it is usually due to a low pressure system passing to our south that causes "upslope" winds. When the air moves toward the mountains, it rises with the terrain. When air rises, it cools, causing the water vapor it carries to condense into precipitation. If it is cold enough, the precipitation falls as snow. Upslope events can last several days and drop copious quantities of snow. If you lived in Denver in March 2003, you know what we are talking about!

This is a time of year when weather patterns change across the United States. The Polar Front moves farther south with the approach of winter. Lower sun angles and shorter days mean less incoming solar energy, and thus, cooler temperatures. Precipitation patterns largely depend on the position of high and low pressure. For most of this fall, Colorado has been dominated by high pressure. We can expect to remain below average on precipitation until we see more low pressure systems coming our way.

We salute the volunteers of CoCoRaHS who trudge out every morning to record the latest snowfall. Just about anyone can become a CoCoRaHS volunteer. Please visit http://www.cocorahs.org for further information.

BONUS COVERAGE: Winter Weather Preview

With the approach of winter, we thought a preview of what we might expect would be in order. Klaus Wolter of NOAA's Earth System Research Laboratory says the late-fall season (Now - December) looks somewhat dry for Arizona, New Mexico and Colorado. This would be consistent with La Nina type atmospheric circulation anomalies. Wolter says the late-winter season (January - March 2009) looks more promising for moisture in the north-central Colorado mountains, but dry conditions may prevail over the northeast Colorado plains, again similar to typical La Nina conditions on the plains. Wolter indicates in his forecast that the overall ENSO (El Nino-Souther Oscillation) pattern remains unsettled. That means that we could see a return to La Nina conditions, or a transition to El Nino as we head into 2009.

People commonly refer to the El Nino-Southern Oscillation as simply 'El Nino'. El Nino is a global coupled ocean-atmosphere phenomenon. The Pacific ocean signatures, El Niño and La Niña are important temperature fluctuations in surface waters of the tropical Eastern Pacific Ocean. The name El Niño, from the Spanish for "the little boy", refers to the Christ child, because the phenomenon is usually noticed around Christmas time in the Pacific Ocean off the west coast of South America. La Niña, similarly, means "the little girl". El Nino conditions often means big snowstorms for Colorado, while La Nina often brings mild and dry winters.

According to Wolter, the latest La Nina event just about disappeared last summer, but it's kept an atmospheric 'footprint' in terms of precipitation patterns. Most of the forecast models are indicating near-neutral conditions for the upcoming winter. However, Wolter says a return to La Nina is still possible because moderate to strong La Nina events like the most recent one, often make an encore performance.

If you'd like to visit Klaus Wolter's web page, please enter this address in your browser:

http://www.cdc.noaa.gov/people/klaus.wolter/SWcasts/index.html

November 11, 2008

Bands of heavy snow dumped 4-8 inches of snow on the northeast corner of Colorado on Monday, with the most falling over northern Yuma county. The storm that brought that snow missed Denver for the most part, with only a few flurries in the metro area. The storm system will swirl into Kansas today and head away from the region. IN the mountains, a strong northwest flow aloft will keep snowshowers in the forecast through the day, with 3-6 inches of snow possible on northwest facing slopes.

Officially, we've only received a 'trace' of snow in Denver, but some accumulation has been measured in the foothills and along the Palmer Divide. A 'trace' of snow is anything from one flake up to 1/10 of an inch.

Our first snow is late this year. The average date for the first snow in Denver is October 19th.

The earliest measureable snowfall was September 3, 1961 and the latest November 21, 1934. Over the last few years our first snows have been as follows - 10/22/2007... 10/18/2006 ... 10/10/2005 ... 11/01/2004 ... 11/5/2003 ... 10/25/2002 ... 10/05/2001 ... 09/23/2000. While it will not be a big snow, it may indeed be our first this season.

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