I harped and harped on it Thursday and Friday. “You’ll either be in it, or out of it, there really isn’t a dividing line”. I was talking about the cold air and the resultant clouds and light precipitation that caused quite a few headaches on the roads for those trying to get around on Saturday in particular. On Sunday as I went into the grocery store at noon, Woodland Park was at 54 degrees with a lot of sunshine and most of the metro areas were in the teens and lower 20s.

We’re still dealing with this today and being that I’m now in the office I can show you some graphics to illustrate this concept of the shallow and dense cold airmasses. Check out the NWN shots from around 230.

 Eads at 230 was still holding on to 39 degrees and still had quite a bit of low cloud cover. Below you see that Canon City had cleared out and made it to 50 degrees, but at the same time the Pueblo airport was only at 44.

Briargate, one of the higher areas in the Colorado Springs metro was running about 6 to 8 degrees warmer than many neighborhoods near downtown. As you look toward Pikes Peak in that shot, the haze at the base of Pikes Peak (sorta looks like a Bob Ross painting!) represents where the deeper cold air was. A reminder that it is lower downtown along Monument and Fountain Creeks than it is in the Briargate neighborhood. This is important because the cold airmass that moved in Friday night is very dense (more air molecules in a given area) than the relatively warmer air over the mountains. Because of gravity, this air acts “heavy” and is most noticable over the lowest areas. Check out the visible satellite imagery from a little after 230. It shows the low clouds associated with the deepest part of this cold airmass hanging out along the Arkansas River Valley (the lowest area in southern Colorado).

The image above right very nicely illustrates how I describe this cold air. As it sloshes up against the foothills, it is a lot like ocean waves crashing on the seashore. It moves up the beach, then back out, then back up and your feet are either wet or not, there really isn’t much of a dividing line. In this metaphor, the water is the cold air and the beach is our local terrain. Many times over the winter months we’ll find that areas in the foothills and over the mountains will end up warmer than some of us at lower elevations. When this happens, you know that a cold and dense airmass from Canada has moved in for a few days!

By the way, many times in these scenarios we know we can not “nail” the temperature forecast, we simply try to make the point. It is next to impossible to pinpoint where the border of the cold airmass will be at any given time and it will move up into the foothills and back down through the course of the day. Many times the difference between being in the cold air and out of it can be 20 degrees or more with a dividing line of less than 1/4mile. In these situations we just hope to send you out the door with an idea of what is happening overhead…

July of 2008 was the driest since we’ve kept weather records in Colorado Springs and in the top 10 driest Julys on record in Pueblo. Most of our region was way behind on moisture. As July closed and August began, the southeastern corner of the state was in a significant state of drought according to the US Drought Monitor.

While this year isn’t going to go in the record books as being in the top 3 wettest for the Springs, we are above average by about an inch. However, it is the second wettest on record in Pueblo and most of the area has been pretty wet since mid-Spring and especially the last couple of weeks. Today’s Drought Monitor shows quite a different picture than a year ago! What a difference a year makes! 

Are you wondering how that pothole appeared on your street?  This time of year, when rain or snow seeps through cracks in a roadway, moisture reaches the soil below.  That water freezes as temperatures drop (even with the warm days we’ve had, we still get below freezing at night), causing the ground to expand, which pushes the pavement up.  When temperatures rise again during the day, the ground contracts, leaving a gap between the pavement and the soil as the water melts.  Potholes form when vehicles drive over the area where the gap exists – the pavement cracks and drops into the hollow area below.

Viewer Tip: In most areas, you can report potholes to your city streets department or CDOT on major highways for repair.  If you’ve hit a pothole in your vehicle and notice steering problems, low tire pressure, or visible bulges or blisters on your tires, it is a good idea to have a professional check your vehicle for damage and make any necessary repairs.

A temperature inversion is a reversal of the usual pattern in which temperature decreases with increasing altitude. During a temperature inversion the lowest temperatures are closest to the ground; warmer temperatures at found at higher altitudes. An inversion set up quickly early in the evening and you can see it displayed clearly here at 10 pm.

The station with the lowest elevation we have on this map above is at the station, adjacent to Fountain Creek. The stations east and north of here are higher and its pretty obvious to see the temperatures were warmer at this time as you increased in elevation. Even at 1am on a bigger scale, Denver, Colorado Springs and Trinidad (higher elevations) are warmer than Pueblo and areas along the Arkansas River, Limon where the weather station is along a creek and the San Luis Valley. Note the 28 at Monarch Pass (above 10,000ft)…you’d think it would be colder then Pueblo, right? Inversions are common this time of year, especially when the wind is light and the atmosphere is dry. Inversions are the reason Pueblo is usually colder than Colorado Springs at during the winter months.

I received the following email from viewer Brent Rohde:

Hello, my name is Brent Rohde. I am spending my first summer in Colorado Springs as a resident. I have a question about an apparent weather trend and feel confident that, in addressing it to you, I will receive a knowledgeable and intelligent response.

It seems that most summer days start bright and sunny until midday when looming gray clouds from the west march inexorably east over the mountains to shroud the city from sunlight until early evening, sometimes even spilling rain. WHY? What conditions cause this rather unwelcome trend? Is it heat-and-altitude created? I sure would like to know.

Sincere thanks in advance for taking the time to reply when you can,

Brent Rohde

Brent,

You are an astute observationalist, something that is a good trait to have as a meteorologist! People that have lived along the Colorado Front Range for more than a summer are two are well aware of our diurnal cloud pattern that you question about. Actually, you are on the right track to the answer in your email.

The daily clouds that develop around late morning to mid-day over the mountians are driven by a process called convection (in this case its actually called moist convection). As the earth’s surface heats unevenly (air over a parking lot will end up hotter than an adjacent grass field), the warmest pockets of air begin to accelerate upward as they end up less dense than the surrounding (relatively cooler) warm air. If this parcel ascends enough, water vapor will begin to condense as the temperature of the air (which is cooling at a rate of 5.5 degrees Fahrenheit per 1000ft) approaches and reaches the dewpoint. When this condensation occurs, a cloud is born. The condensation of water vapor into liquid releases heat, further warming this air pocket and often allows this process to continue and feed on itself, eventually producing precipitation.

So why does this convection seem to occur, or at least begin, over the mountains in Colorado?The anwer is the temperature lapse rate…or the rate at which the temperature cools in the vertical. The higher the lapse rate (the faster the air cools as you ascend) the more unstable the atmosphere is and the easier it is for the process of convection to begin/occur. Due to the elevation in the mountains the usually warm surface temperatures are closer to the cooler air at 25,000-30,0000 than the just slightly warmer surface temperatures on the plains. The image above shows the temperature lapse rates between about 12,000 and 25,000ft. The areas shaded in orange are values greater than 8.5°C/Km. Note that most of the mountain areas are at or above this value while the southeastern plains of Colorado are not. A plot of lapse rates looks like this almost every afternoon (the fact that the plains of northeast Colorado is shaded in orange is due to a passing wave in the atmosphere with some cooler than usual air aloft…normally this area has about the same values as the plains of southeast Colorado) and shows very nicely where the clouds (and usually thunderstorms) first develop each day.

Once this process begins the large scale west to east flow aloft across the northern hemisphere will push the clouds/storms eastward over Colorado Springs as the afternoon wears on. As you have already noticed in your short time here…this process occurs almost every day. Sometimes I wonder what would happen if I made the same forecast once in early May (High of 75-85 with a 20% chance of storms) and left for the summer? Yeah, probably not, but a guy can always dream!

Thanks for the email!

I got an email tonight from Lawrence, who lives 20 miles east of Falcon. He said, “We just totaled the rain gauge readings from April 1 until today. 2.61 inches. This is .3 less than the great drought of a few years ago (2002).”

That got me to do some digging. Interestingly enough, the local Weather Service in Pueblo had done some checking of their own the other day. Below are some of their findings (the rank is in terms of driest January 1-July23 since records have been kept at each individual station - the periods of data differ for different locales)

You can see that for the official observation at the Colorado Springs Airport, its the driest first 204 days of the year on record! In 2002, which now ranks 3rd, we had 4.23″. Pueblo Reservoir ranks 2nd driest ever and its pretty obvious from the other numbers that we need some rain! While we have had some thunderstorms over the last few weeks, they don’t help everyone out. They’ll hit one neighborhood hard (two weeks ago parts of Black Forest had 2-3″ on a Friday night), while Lawrence has had that amount as a total since April 1st.

Checking with the USDA’s Drought Severity Index confirms…we’re in a drought. The southeastern corner of the state has extreme to exceptional drought conditions. We’re tracking the remnants of “Dolly” as it may bring storms Monday…I’ll blog on the current long term prognostications by the Climate Prediction Center through the end of the year early next week.  Have an enjoyable and relaxing weekend!

They’re going to be common over the next 6 weeks or so and will be responsible for quite a few thunderstorms so I thought I’d talk about them tonight as I caught a really good example on Tuesday and most of our storms tonight were produced by one.

Outflow boundaries are the leading edge of rain cooled air that is moving away from the parent thunderstorm. This air is usually denser than the air it is moving into and thus acts like a mini cold front, lifting the air its moving toward. This lifting can occasionally produce a thunderstorm that will develop, grow and strengthen while the boundary continues to lift the air and then usually collapses as the boundary (and lift) moves away. For the most part they produce brief thunderstorms that would not otherwise have existed.

These outflow boundaries can typically be detected on radar as “thin lines” of low reflectivity. This results from the convergence of air along the boundary, lifting things like dust particles and bugs. In this example I’ve annotated the outflow boundary in a yellow dashed line, with the rain cooled air from the Front Range meeting up with warmer air moving in from the southeast. The weak thunderstorms south of La Junta were quickly developing as this outflow approached, they reached peak intensity around 6:00pm and were gone by 6:30 as the outflow continued to the southeast.

If more than one outflow boundary is present, the collision of these features typically results in thunderstorm production, usually at a pretty rapid rate that can occasionally result in severe weather. Outflow boundaries running into existing thunderstorms can sometimes strengthen them, but occasionally can cut-off the warm and moist inflow air, thus suffocating the storm of its fuel source. Marty and I were storm chasing once just east of Last Chance, CO and were watching a storm that was in the process of producing a tornado. All of a sudden the base of the storm elongated and started moving toward us as outflow from storms to the north blasted into and through the storm, effectively killing it…Mobile radar wasn’t readily available at the time, but when we got home (after a long drive!) we were able to see an outflow boundary move away from a storm on the Colorado/Wyoming line move southeast over about a 90 minute period and run into our storm…Bummer!

It’s going to be a very quiet day on the weather front so I thought I would take the opportunity to showcase the STORMTRACKER 13 Neighborhood Weather Network as the sun was rising today, just some pretty shots to share on a beautiful summer morning…

We love having this tool and will be expanding it over the next several weeks as we look to continue bringing you the best local coverage available in southern Colorado…

The moisture associated with the summer “monsson” is absent from most of the west, but not too far away from us.  Check out the water vapor imagery below:

Where you see the black coloring on the map the atmosphere overhead is very, very dry.  Notice the extremely dry air over Colorado this morning which is why we are not expecting much, if any shower activity even over the mountains, this looks to remain true for most of tomorrow too.  If you’re hoping for rain all is not lost, the white shaded areas show where the moisture associated with the summer “monsoon” is currently located, and there’s quite a bit of it just to our south.  Indications are that this moisture will slowly drift northward bringing a return to daily thunderstorms and slightly cooler weather starting this weekend and continuing well into next week.  Of course we will be tracking that potential over the next several days, and we’ll let you know how good our chances for rain will be as the moisture starts heading our way.  Have a great day and stay cool!

Marty V

Welcome to July, typically the hottest month of the year in Colorado. More specifically, the 12th through the 24th is climatologically the peak of summer temperature-wise in Colorado Springs as the average high temperature tops out at 85 degrees. In Pueblo, the stretch is a little longer and the average high reaches 92 from the 9th through the 27th.

Our threat for tornadoes drops quite a bit this month as the atmosphere tends to become stagnant, but its this stagnation that eventually allows the monsoon to get going as moisture from thunderstorms over the mountain ranges of central Mexico gets recycled each afternoon and gradually moves northward into the desert southwest and Colorado. This usally happens toward the tail-end of the month or into August. Its during this time that flash flooding becomes a major concern as slow moving thunderstorms capable of dropping copious amounts of rainfall in a short period of time become possible over our region. Exercise caution when recreating in canyons, river beds and other low-lying areas (like dry washes) as they can become violent rivers in an instant.

Speaking of moisture, now is a good time to look at how we’re doing so far this year. You can probably guess that its not very good with the recent rash of wildfires we’ve had (a pretty good sign that we’re dry) both in the mountains and on the high plains. The 2.92″ of rain we’ve officially collected at the Colorado Springs Airport is well below the average rainfall of 8.04″ by more than 5″. In Pueblo, we’re 1.75″ short of the average rainfall through June of 5.63″ as we’ve measured just under 4″.