Dense Fog Advisory issued October 5 at 10:52PM MDT expiring October 6 at 10:00AM MDT in effect for: Cheyenne, Kit Carson, Yuma
After a long stretch of dry and quiet weather, the storm track has gotten back on line across the Rockies and we are finally getting some much needed moisture.With this most recent storm, we have had a number of questions about the weight of snow. The main thing that meteorologists look at to determine how much snow will fall is the ration between inches of snow and the actual amount of liquid water. The higher the ratio, the lighter and fluffier the snow. The typical ratio is a 10:1 - meaning that 10 inches of snow is produced from 1 inch of liquid precipitation. The "champagne powder" that our ski resorts like to brag about is sometimes a 20:1 ratio - really dry and fluffy! In the Midwest and the East, the warm, wet snowstorms can bring a slushy 6:1 ratio - that is the stuff that really gives shovelers a sore back.In the big storm of March 18-20th of 2003, the official Denver total for snow (measured by the National Weather Service at a site near the old Stapleton Airport) was 31.8 inches of snow. Many other spots around the city had much more - up to nearly double that total in the foothills between 6500 and 8500 feet. The melted total for the storm was 2.80" for Denver's official total - so a little closer to an 11:1 ratio from this storm.An inch of rain on an acre of land equals 27,000 gallons of water. The storm total of 2.80 inches means that the 31.8" of snow equaled 76,500 gallons of water on an acre. Since a gallon of water weighs about 8.33 lbs, that snowfall would weigh approximately 638,000 pounds per acre. If you convert that over to tons, the total weight of the snow was about 320 tons per acre. That is for about 32 inches of snow, so for an average 10:1 or 11:1 snow/water ratio, the snow weighs about 10 tons per inch per acre. That might explain why your back hurts so much from shoveling and why all those roof collapses occurred, as well as the tree damage.When storms set up just right to dump on Denver and the Front Range, they need to be in southeastern Colorado. A low pressure area stalled over southeastern Colorado will swirl moisture into the high plains all the way from the Gulf of Mexico! This type of system acts as a funnel to bring all the moist air our way, press it up against the mountains and create a literal "snow machine".The biggest storm in Denver history, 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!The biggest storm in a 24 hour period on record for the USA was in April 1921 at a small locale in Boulder County called Silver Lake (it no longer is found on most maps). They picked up over 76 inches of snow in just 24 hours!The greatest annual snowfall on record for the USA is from the Paradise Ranger Station in the Cascades of Washington state. In 1955-56, they tallied an amazing 1000 inches of snow! Thursday's storm system packed a punch as it crossed Colorado, dumping one to feet of snow over the mountains and eastern plains. The storm has been winding down in the Denver area overnight, but heavy snow, strong winds and very cold temperatures made for blizzard conditions over the southeast quarter of the state all night long. Many roads are closed over the eastern plains and travel will remain difficult east of Denver through the morning.Morning commuters will still face challenges in Denver and along the I-25 corridor as the roads will be icy, depsite the best efforts of CDOT crews through the night. Fortunately the weather will improve dramatically during the day, with sunshine returning - although it will stay pretty chilly. High temperatures are expected to only climb into the low 30s, but the winds will be lighter.The weekend will warm a little, but we will not see those 60s and 70s of a week ago. The weather has finally turned into the winter-like pattern that we have been lacking for most of the past several months. Another storm system will be heading toward Colorado by Sunday night, with more snow on the way for Monday. It is too early to tell if the next storm will bring heavy snow to Denver, but there certainly is a chance of accumulating snow again by early Monday.The storm over the past 24 hours has dropped about 8 inches of snow on Denver - officially. This boosts our seasonal snowfall to about 25 inches. This is still well shy of our average snowfall, which should be about 50 inches by this time. We are now out of the running for this winter to be the least snowy on record for Denver. The least snowy winter on record was 20.8 inches in 1888-89. After many near misses, Denver and the Front Range is finally getting a heavy does of snow! All the forecast models have been hinting at this all week and we're finally going to see the big snow that March so often brings!The storm system moving in from the west will swing into the four corners and slide through southern Colorado and into the Oklahoma panhandle today and tonight. This track sets up for a good, strong and moist upslope flow that will create perfect conditions for a heavy, wet snow across northern Colorado, including the front range urban corridor.Right now, the models are showing a snow range of about 12-15 inches in Denver with higher amounts in the southern and western suburbs. Areas in the mountains and foothills will see upwards of 2 feet through Friday morning. A BLIZZARD WARNING is in effect until 6 AM on Friday. Many schools and businesses have already closed up in anticipation of very poor traveling conditions across the eastern half of the state. With the weather deteriorating today, stay home if possible.This storm will be a heavy hitter, but will only stick around for a day, moving quickly east of the region on Friday and giving us a break before another fast-moving system swings into the region on Monday bringing another chance of storms. We missed another big storm early this week as an intense low pressure system developed just a bit too far to the northeast of Denver and dumped heavy snow on Wyoming and the Dakotas. Typical of this winter, there have been big storms moving across the nation, they just have not tracked in a way that brought snow to the Front Range. Our luck should change with the next storm, might actually get a storm that could dump heavy snow in Denver Thursday and Friday.Most of this winter has been very dry and windy across eastern Colorado. This is typical of a La Nina winter for our part of the state. The terms La Nina and El Nino are frequently mentioned in weather reports, so here is a little more information about them.La Nina is a change in the flow of Pacific Ocean waters. During times of La Nina, translating to "the girl child," winds increase causing the warm surface waters along the West Coast of South and Central American to be transported eastward. The removal of these warm waters allow for the cooler water underneath to surface, thus resulting in a drop in sea surface temperatures along the coastline. Consequently, warmer waters "pile" up along the Eastern Coast of Australia. This is the opposite of the what is observed with an El Nino event, which is the reverse of La Nina. The terms are used because the phenomena often show up late in the year, or around Christmas time. The region, being heavily Catholic, linked the weather phenomena to the Christmas season.This large scale circulation of ocean waters and variation of sea surface temperatures can significantly alter the weather right here in the United States, particularly the Southwest. If a La Nina event were to occur during the winter season, the lack of warm waters result in less evaporation of water vapor into the air. This inhibits the production of precipitation producing clouds that would move through the continental US. Therefore, cooler sea surface temperatures means less evaporation which means less snowfall in the Rockies. La Nina episodes have also been linked to warmer winter temperatures in the Southwest. Does this sound familiar? This winter we have seen temperatures way above average, and moisture levels way below average. We even broke the 137 year old record set in 1872 on March 2nd as we climbed to 76 degrees! And yes, sea surface temperatures and wind data have indicated that the Pacific Ocean is indeed in the midst of a La Nina episode.While new long-range forecasts indicate weakening La Nina conditions, the dry spell is still hanging on. Klaus Wolter of the University of Colorado Climate Diagnostics Center and NOAA's Physical Science Division says La Nina conditions may be weakening in the coming months, but a return to 'normal' precipitation may be a bit further off. Wolter's forecasts take into consideration the global weather patterns apparently caused by ENSO, (El Nino Southern Oscillation).Wolter says La Nina typically lasts for longer than one year, as evidenced by it's "encore performance" in early 2009. While this has been good for our mountain snowpack, the plains remain bone-dry. However, Wolter says even La Nina Aprils allow for wet spells, and a few spring storms are always possible. The current long-range prediction is that La Nina will continue, but weaken. As for whether we can expect a move to 'neutral' or even El Nino conditions, the jury is still out. Wolter says that, overall, the meteorological winter season of January - March will likely end up on the dry side. With Spring fast approaching, the big weather concern will go from snow (or lack thereof) to severe weather. Colorado's biggest severe weather threat is large hail, and storms here in Colorado can produce hail as small as a pea to as large as a softball. Currently, a storm is called severe when it produces hail measured at penny-sized or 0.75".Starting on April 1, the National Weather Service will change this criteria from 0.75" to 1.00". This change will also take effect in Wisconsin and Minnesota starting April 1 and will be gradually adopted by Weather Service Offices across the country into the summer.The change was due in part to research that indicated that hail smaller than 1-inch typically did little if any damage and did not constitute warning as it was not threatening to life and property. Research shows that stones of at least 1-inch are needed to cause damage to property. The winter of 2008-09 could go down in the Denver record books as one of the driest since records began in 1876. With a dry and stable air flow in place over the state, it doesn't look like we will have any significant precipitation on the plains in the coming week. For Monday and Tuesday, a downslope flow will keep us dry and mild, with high temperatures topping out near 70 in Denver. A weak and dry cold front will move through northeast Colorado on Wednesday, dropping our temperatures to seasonal levels in the 60s for the rest of the week. The mountains may receive a bit more snow from this system, but don't expect any major precipitation on the plains.With March being our snowiest month, climatologically, the big question is: When is that big snowstorm going to hit? The answer lies in the upper-level wind patterns. While the persistent west-to-east flow stays in place, precipitation on the eastern plains will be limited. Areas east of a large mountain range experience a "rain shadow" effect. Air flowing up a mountain slope will cool and the moisture in it will condense due to colder temperatures and lower pressure. By the time the air crosses the mountain range, most of the moisture has been precipitated out. As the air begins moving downslope on the eastern side, it warms due to compression, (higher pressure near the surface). What little moisture remains won't condense due to the warmer temperature of the air. Warmer air can hold much more moisture than cold air.Hopefully we will see a change in the upper-air patterns sometime soon. Eastern Colorado needs a very wet spring to soak the soil before things dry out and get hot this summer. The most recent system mostly benefitted the mountains, where 8 to 16 inches of snow fell. On the plains, a fast moving band of moderate snow came early Tuesday and dropped a few inches of snow, especially north of Denver. The timing of the snowfall snarled the morning commute, but most of the flakes finished by daybreak and sunny skies melted away the icy conditions on the roads by mid-morning. The moisture managed to put a minor dent in the dryness, not enough to break our drought conditions.The snowflakes in our typically snowy month have been few, at least across the plains. Denver has seen only 18 inches of snow since September, and State Climatologist Nolan Doesken says the plains are under 'moderate drought' conditions. To top it off, this winter season may go down as Colorado's driest since 1872 when meteorological records began in Denver. So, when will our snowiest month start behaving like it? Our long-range forecast models are still showing an unfavorable weather pattern for eastern Colorado's moisture concerns. Our mountains have fared well this winter season, but the plains remain dry.The problem this winter has been that the storms have been moving too quickly, and too far to our north to bring us the kind of cold air and moisture needed for a large snowstorm.Air flows in a counter-clockwise direction around low pressure systems. When storms move north of Denver, we are under a westerly flow, which is not ideal for snow on the east side of a mountain range. However, when a low moves south of us, we get winds from the east. This 'upslope' flow allows moisture in the air to condense and precipitate as it rises to a higher elevation. Sometimes strong low pressure systems can tap into moisture from the Gulf of Mexico. When this happens, copious amounts of snow can fall on Denver.Moisture and atmospheric dynamics must work together, and when they do, eastern Colorado can quickly recover from drought conditions. If you remember back to 2003, our March snowstorm pushed our soil moisture to 104% of normal in just two days.At this time in the second week of March, there are still no big snows on the horizon, and the storm tracks are not yet favorable. Our weather patter for the next week is above average temperatures and sunny skies. So for now it appears as though March will continue to act like the lamb it came in as. We will have to wait a bit longer to see if March will make good on moisture. A couple of cold fronts will be the driving forces in our weather over the next few days. The first front pushed into the state last night, bringing a few inches of snow to the northern and central mountains. Another cold front will move our way early next week, with more mountain snow and rain or snow for Denver and the eastern plains Monday afternoon and Tuesday.Friday will be dry in Denver, with no issues travelers, but the northern and central mountains will experience periods of snow throught the day. By Saturday, clouds will thicken and light snow will fall over the northeast quarter of the state. Totals in the metro area should be in the 1-2 inch range, with the snow mainly melting on the roads, and only accumulating on grassy areas. By Sunday the temperatures will bounce back into the 50s, before the next cold front brings colder weather again Monday and Tuesday.The colder weather will make it feel more like March, but we still need to get some good soggy storms over the eastern plains. The extended forecast for the second half of March does not bode well for the parched plains of eastern Colorado. According to the Climate Prediction Center in Washington DC, the eastern third of our state is forecast to be drier and warmer than average. The third month of the year is often a stormy one, averaging nearly a foot of snow in Denver. We are currently sitting with less than 17 inches of snow for season, about a third of where we should be at this point. Although the mountains have a good snowpack, we really need a good soggy storm on the plains. With the extended outlook calling for mild and dry weather in March (keep in mind, one big storm is all it takes), we may need to pin our hopes on April and May.In addition to the latest long-range forecast from the Climate Prediction Center, there is another prediction that may hold some hope for eastern Colorado's moisture deficit. Klaus Wolter; a Boulder scientist who prepares the experimental forecasts, says that La Nina conditions continue to linger, which usually does not bode well for precipitation across the eastern plains.However, Wolter's analysis indicates a possible weakening of La Nina conditions over the next two months. If his forecasts for late-spring (April - June) verify, it could mean a return to near-normal conditions. This may translate to increased, or wetter-than-average precipitation for the eastern Colorado plains.Wolter's predictons have been quite accurate, zeroing-in on the El Nino/La Nina phenomenon, and it's impacts on the southwestern United States. The El Nino Southern Oscillation (ENSO) is a phenomenon that has the potential to affect weather conditions worldwide. The phenomenon is a disruption in the ocean-atmosphere system in the tropical Pacific. El Nino conditions are studied by many scientific groups, including the Cooperative Institute for Research in Environmental Sciences at the University of Colorado, Boulder (CIRES). While eastern Colorado usually experiences drier-than-average conditions during a La Nina episodes, moisture often increases when ENSO returns to "neutral" status. One major benefit to La Nina conditions is above-average snowfall for the Colorado mountains. Thanks to this season's La Nina conditions, snowpack in the high country is 112% of the long-term average.ENSO swings between El Nino and La Nina conditions every few years, due to changing direction and intensity of the trade winds. The result is warmer, or colder, than normal sea water in the east Pacific. Rainfall patterns shift toward warmer water, and global weather patterns also change with El Nino.Here's a link to the Climate Prediction Center, where you can obtain the latest maps, showing long-range temperature and precipitation forecasts: http://www.cpc.ncep.noaa.gov/ Tonight is the night to take the family to the Denver Museum of Nature & Science! Their new exhibit "Nature Unleashed" is all about severe weather and other natural phenomena and is a show that you will not want to miss! Tell the folks at the museum that you heard about it from 7News!A new exhibit called "Nature Unleashed" has opened at the DMNS and will continue through May 3. Visitors will be able to get a thrilling, but safe "hands on" experience with earthquakes, volcanoes, hurricanes and tornadoes! Exciting demonstrations will enable visitors to learn about these disasters and how researchers are studying them to help save lives!This evening - March 5, Colorado Storm Chaser Tim Samaras will be giving a lecture on his work with tornadoes and showing off amazing videos of his tornado chases. Tim is the real-life version of the characters in the movie "Twister" and has been within just a few hundred yards of devastating tornadoes. Tim has designed special bullet proof probes that he deploys in front of tornadoes and has actually videotaped the inside of a tornado. This lecture begins at 7:00pm in the IMAX theater. If you cannot make the lecture, the exhibit will allow you to stand in a room with a 360 degree view from inside a tornado! Feel the power, hear the roar, and be in the tornado!