The Weather Wire
March 2004 Volume 11 Number 3
Avg High 41.9
Avg Low 19.8
Snow - 8.9"
Season Snow - 20.9"
Precipitation - 0.21"
Avg High 53.7
Avg Low 25.4
Avg Snow - 11.7"
Avg Precip - 1.28"
Pollution Such a Problem Here??
Flying into Denver you notice it right away!! From above a large hazy cloud envelopes the entire metro area. Once on the ground you can see the mountains only vaguely as haze obscures the view to the west. Although Colorado has its share of crystal clear days when the view of the mountains is awesome, during the Winter months there are more days than not where it is hard to see the foothills let alone the mountains. So why is this and why are the Winter months especially prone to high pollution days??
The major polluter for the Front Range is the car, but we also have to include smoke from fire places, sand and salt from our streets, jet exhaust form DIA, dust and industrial smoke. All these pollutants are produced every day along the Front Range and some days will be clear while other days will be murky! So why the difference??
Two major features affect whether we have a high pollution day or a nice clear day. One is the natural topography of the Front Range with the foothills and mountains to west. The topography never changes but still is a major factor in our pollution! Weather is the other factor here and especially when combine with our topography plays a major roll in either dissipating the pollution or trapping it.
Going into a bit of thermodynamics, in the ideal atmosphere as you go up from the ground the temperatures cools 5.5 degrees for every thousand feet you rise. Air that is heated at the ground will rise as long as it is warmer than the surrounding air. Once it encounters warmer air it will no longer rise. On an average day the air will rise taking the pollution with it and dispersing it in the upper atmosphere where the prevailing winds carry it off to the east. Now here is where Winter months play a key roll in trapping pollution along the Front Range. Many days during the Winter the air at the surface is colder than the air 2-3 thousand feet above. This can be due to snow cover on the ground creating a cold layer of air, or a shallow area of cold arctic air that typically pushes in from the north or even just a weak upslope northeasterly flow off the plains.
When we get colder air at the surface with warmer air above this creates what is called an inversion. As a parcel of air rises it encounters this warmer layer. It is no longer warmer than the surrounding air and as a result quits rising and in essence is trapped below this warm layer and with it the pollution with it. Until the cold layer of air is warmed enough or moves out the pollution is trapped and continues to build up under this warm layer cap. This type of situation can persist for days and result in visibilities of less than a mile.
The other factor in creating an environment conducive to pollution is the natural barrier to our west called the Foothills and mountains. Many days during the Winter months cold air drops down from Canada and winds turn to an northeasterly to easterly direction. This takes the air and the pollution and pushes it up against the foothills. This being a hard natural barrier the pollution having no where to go just builds up along the foothills and then begins to spread eastward over the city. Again during the Winter months this type of pattern can last for days resulting in high pollution days as the pollution has no where to go so just gets thicker and thicker.
In contrast during the Summer months it is rarer to have colder air at the surface and aloft so high pollution although they can occur during the Summer are more common during the Winter when we have colder at the lower elevations.
Until technology gets us past the gasoline engine, the burning of petroleum and coal for energy, pollution will continue to be with us. The weather patterns will not change nor will the foothills and mountains to our west. It is up to us to change how we drive how we use energy and what types of energy we use. Until then pollution and a very hazy view of the mountains will continue to be with us.
Although the official snowfall and precipitation amounts showed below normal precipitation across the Denver Metro area, most locations actually recorded above normal precipitation. A look at the map shows only moderate drought conditions across the Front Range, though extreme conditions still exist along the eastern border with Kansas, southeastern Colorado, and extreme west Colorado.
The map below shows forecasted temperature deviances for the February 2004 time period. As can be seen, above normal temperatures are expected for all of Colorado for February.
The map below shows forecasted precipitation deviances for February 2004. Normal or near normal precipitation is expected for February 2004 across Colorado.
As can be seen in the below map, conditions are expected to continue to slowly improve during through April across much of Colorado. Snow pack is generally at or above normal in most basins, though the South Platte drainages are below normal at this time.
For the eight month in a row precipitation was below normal in Denver with a mere 0.21 inch reported at Denver International Airport. This compares to a normal of 0.52 inch. Again we must note that DIA being well to the east of the metro area traditionally receives less moisture during upslope events. Many areas to the west and south of DIA are not only running about normal, but some areas were above normal for the month. The wettest February was in 1934 with 2.01 inches and the driest was in 1970 with a mere 0.01 inch.
Snowfall for the the month was above normal with 8.9 inches reported. This was 2.6 inches above normal. Again remember that official snowfall for Denver is recorded at the old Stapleton field, a bit closer in to the metro area. DIA received even less snowfall than this resulting in the less moisture. The seasonal total now sits at 20.9 inches. 19.6 inches below the normal of 39.6 inches. There were 7 days during the month with measurable snowfall. The maximum in 24 hours occurred between the 5th and 6th with 3.2 inches. The snowiest February was 1912 with 22.1 inches and the least snowiest February was 1970 and 1992 with only 0.3 inch.
It was a cooler than normal February with an average temperature of 30.9 degrees. This was 2.4 degrees below the normal of 33.2 degrees. However it was not enough to get into the top ten coolest. The coldest February occurred in 1899 with an average temperature of 17.6 degrees. The warmest February was in 1954 with an average temperature of 43.7 degrees. Temperatures this February ranged from a high of 67 degrees on the 18th to a low of -9 on the 12th.
The weather in Denver during March features frequent and rapid changes. Longer days allowing for more sunshine make for Summer-like weather. However, occasional arctic air masses can still plunge southward across Colorado rapidly dropping temperatures with some readings falling to near zero degree readings.
The changeable weather is due to weather elements common to both Winter and Spring. In addition to arctic fronts, Pacific storms still frequently move in from the west and warm moist air streams in from the Gulf of Mexico northwestward into Colorado. When any of these cold fronts collide over Colorado with the warmer air masses, the results can be wild and crazy for the area surrounding the Denver Metro area.
A prime example of the changeable March weather in Denver occurred on March 8th, 1992. The sky was sunny over Denver during the morning hours allowing the temperature to reach 52 degrees by midday. During the afternoon, tornadoes and thunderstorms containing hail developed across the northeast plains including the Denver metro area. A Canadian cold front zipped across the east during the late afternoon dropping temperatures sharply and creating blizzard conditions along the Front Range. the storm dumped 12.4 inches of snow at Stapleton Airport with greater amounts reported across the metro area.
Another example of the variable weather during march was just last year on March 17th a tornado was observed and filmed near Bennett with temperatures only in the 40s. Later in the day the second strongest Winter storm in Denver history was to begin. During the period March 17-21, 31.8 inches of snow was recorded at the former Stapleton International Airport. 87.5 inches of snowfall was recorded in and around the Rollinsville in the foothills west of Denver and 40-60 inch amounts were common to the west and south of Denver.
March is the snowiest month of the year. However, even the heaviest snows rarely stays on the ground very long due to the abundance of sunshine and rapidly moderating temperatures. In addition, March usually has the first Spring thunderstorm of the year and there are still a few days where strong Chinook winds are observed, but the strongest winds are generally near the foothills.
The National Weather Service 30 day outlook for this March expects temperatures to be slightly above normal with precipitation near normal.
Sunrise/Sunset (Denver area)