Sunday, May 24, 2009

5/24 rainfall totals, gustnadoes and landspouts

Lots of things going on in southern Colorado on Sunday, from heavy enough rain for flash flooding (again) on the west side of Colorado to tornadoes and gustnadoes closer to Denver.

Let's look at the rainfall totals first...

.49" - Colorado Springs Airport
.15" - Pueblo Airport
1.54" - 3 miles southwest of Colorado Springs
1.43" - Near 8th and Moreno, Colorado Springs
1.00" - and dime-sized hail. Yoder
.64" - Northern Downtown Colorado Springs
.59" - East-central Colorado Springs
.28" - Fowler
.24" - La Junta
.12" - and 1/4" hail. Cripple Creek
.12" - Woodland Park

Now, on to gustnadoes and landspouts. At least one gustnado was reported near Parker Sunday afternoon.

These are rotating circulations that don't develop from "supercell" thunderstorms (as the big ones do), but appear along the gust front. (That's the blast of wind caused by falling precipitation that spreads out along the ground in advance of the storm).

They're often associated with lines and clusters of thunderstorms.

Most are weak, but some may reach speeds of over 100 mph.

Landspouts develop by a different process...

They develop when rotating columns of air at the surface are picked up by the updraft of a developing thunderstorm. They can form before precipitation in a developing thunderstorm is even detected on Radar.

Damage can be significant, as these circulations can reach F2 on the Fujita scale (the scale that measures a tornado's intensity...and F2 winds can be as strong as 157 mph).

I found a great link, if you'd like more information. Try http://www.srh.noaa.gov/topics/attach/html/ssd96-8.htm

Saturday, May 23, 2009

Rainfall totals from Saturday, 5/23/2009

Thunderstorms deluged parts of southern Colorado, including the Colorado Springs Metro area with heavy rain and small hail on Saturday afternoon. Here are a few daily totals I didn't have time or space to show you on the air...

.53" - Colorado Springs Airport
.40" - Pueblo Airport
1.5" - Yoder (and lots of small hail)
.75" - East-Central Colorado Springs
.59" - Woodland Park (and lots of small hail)
.54" - Monarch
.46" - Fountain
.41" - Widefield
.39" - Cripple Creek
.25" - Northern Downtown Colorado Springs (Palmer High School)
.12" - Salida
.10" - Monument

Friday, May 22, 2009

Storm stats from 5/22/09

Thunderstorms with heavy rain blasted west-central El Paso county on Friday. Flash flood warnings were in effect until 5:30 PM, as 1"-3" of rain fell from southwestern Colorado Springs to the Broadmoor area.

The area near 7 Falls was particularly hard-hit with flash flooding, mudslides and water running 2 1/2 feet deep over nearby roads.

Here are some (less impressive) rainfall totals from elsewhere around the region.
Colorado Springs - .35" - .45" around town.
Pueblo - Trace
Cripple Creek - .6"
USAFA - .27"
Monument - .22"

Thursday, May 21, 2009

The monsoon

Over the next few days, with all of the showers and thunderstorms we'll see across Colorado, you'll hear the term "monsoon" used a lot.

It does NOT, however, mean "buckets of rainfall". It comes from the Arabic word "mausim", which means season...so the monsoon is a seasonal wind.

In the summer, it blows from an ocean onto a continental landmass (such as the famous one that blows across south Asia). The air is coming from an ocean. It's warm and filled with water. Then it's forced to rise up the highest mountains on earth, the Himalayas, and produces huge amounts of rainfall. (Cherrapunji, India recorded almost 905 inches of rain one year during the summer portion of the monsoon).

The part of the story you don't usually hear is the winter version of the monsoon. Returning to south Asia, the winter flow is from Siberia towards the ocean. This is cold, dry air, and doesn't produce "buckets of rainfall".

In North America, we have "The Southwest Monsoon", as moist air flows from the ocean, across the southwestern deserts, eventually finding its way to Colorado. (Like the summer monsoon in Asia).

It usually begins in June, but it's a little early this year.

Wednesday, May 20, 2009

Heating/Cooling Degree Days

One of your recent questions for the blog was "what are heating degree days and cooling degree days, and what use are they to me?"

It's a good question, as you probably see this information in the weather section of your local paper every day.

First, how they're calculated.

Heating Degree Days are determined by subtracting the mean temperature for the day (high+low/2) from 65 degrees. The result is the number of heating degree days. Public utilities and HVAC professionals can use these numbers, compiled over the long-term to determine how much energy will be needed to keep homes and businesses warm through the cold season. (One example is that New York City averages about 5000 heating degree days per season, while Barrow, Alaska averages over 20,000).

Cooling Degree Days follow a similar form, but are used to estimate the amount of energy it takes to cool homes during the warm season. To calculate them, you subtract 65 degrees from the daily mean temperature (formula above).

A cumulative total is kept for each year, allowing the pro's and the energy conscious to estimate the amount of energy required to heat and cool buildings and homes each year.

Colorado Springs averages 6415 heating degree days each year. For Pueblo, the figure is 5413, so in a "normal" year, it's less expensive to heat a home in Pueblo, than in Colorado Springs.

For the warm season, the roles are reversed:
Colorado Springs averages 419 cooling degree days each year, while Pueblo averages 973, which means that in a typical year (if you're lucky enough to have a swamp cooler or air conditioner), you'll spend less energy dollars in Colorado Springs and more in Pueblo.

You can find your local average heating and cooling degree days at degreedays.net, and you'll also find some great references to articles that will tell you more.

Most of us won't use these figures, but they're VERY helpful to professionals involved in the energy, heating and cooling trades.

Keep those questions coming.
M

Tuesday, May 19, 2009

The Pikes Peak Weather Observers

Here in southern Colorado, we have a rich history of observing and recording the weather. In fact General William Palmer once said that no-one would ever accurately forecast the weather here accurately.

To overcome the General's pronouncement, we first needed to make extensive weather observations to give us the background to project weather conditions into the future, and the process began in the 1800s, with the Army's Telegraphers, stationed on Pikes Peak in the 1800s.

They were a brave, tough and creative bunch...and they needed to be.

On top of Pikes Peak, the climate is similar to what you would encounter in the Arctic.

The difference in temperature between the Springs and the top of the mountain is usually greater than between Colorado Springs and Reykjavik, Iceland,

and the US Army stationed telegraphers on the peak from 1873 to 1889, and these men were the astronauts of their time, living at what they thought of as the top of the atmosphere.

They reported wind speeds of over 100 mph at times, hailstones as big as pumpkins and thunder loud enough to deafen them for weeks at a time, though they may have exaggerated just a bit.

They certainly exaggerated some of the other reports they telegraphed to the rest of the world.

On December 6, 1873, Sergeant Robert Seyboth telegraphed a message that made headlines world wide..He said that as he was passing lake Moraine, he saw a huge sea serpent at least 100 feet long.

As he fled down the trail, he encountered several Utes who told him the monster was particularly fond of their tribe, having eaten 7 since March.

Sergeant Seyboth was creative, but he was an Amateur compared to Sergeant John O’Keefe, who reported Pikes Peak erupting (which is a pretty good trick, since it isn’t a volcano), and during the Summer of 1876, he telegraphed that on a particularly windy day, he and his wife had gone outside to pile more rocks on the roof of the signal station to keep it from blowing away. While they were outside, they said, the Pikes Peak Pack Rats ate their infant daughter. He followed it up with a sad photo of the grave and wooden headstone.

The report horrified a nation, until after a little checking it was discovered that there was no wife, no daughter, and that the Sergeant’s cat (which had died of natural causes) was buried beneath the pile of stones.

The US Army signal corps observers on Pikes Peak may have had a creative streak, but they also braved some of the harshest conditions on the planet and helped us to better understand this regions fascinating weather.

A trip to your local library will get you more information, and at least one volume cataloging the stories of Sgt. O'Keefe.

Thursday, May 7, 2009

Derecho - A damaging wind

Today's question comes to us from Micki, who wants to know "what were those damaging winds that blasted across Alabama earlier in the week. They called them a name I hadn't heard before".

Thanks Micki, those damaging winds were called a "Derecho", a widespread and long lived windstorm that is associated with a band of rapidly moving showers or thunderstorms.

Derecho is a Spanish word which can be defined as "direct" or "straight ahead", and these powerful straight-line winds can do considerable damage, and the area of damage can extends for hundreds of miles.

To see the impact they had on Alabama earlier in the week, try the following link. http://www.nbc13.com/vtm/news/local/article/alabama_storm_damage_caused_by_derecho/71027/

Derechos are associated with bands of thunderstorms (which may include some supercells thunderstorms), which show up as a curved shape (or "bow echo") on radar screens. To see 2 bow echoes on radar, point your browser to this link:
http://www.ask.com/bar?q=bow+echo&page=1&qsrc=0&ab=2&u=http%3A%2F%2Fwww.theweatherprediction.com%2Fhabyhints2%2F386%2F

So, how strong can they be? To start with, winds in a derecho have to meet the National Weather Service's requirement for severe thunderstorm winds (58 mph or stronger) at most points along the path of the storm.

Gusts stronger than 100 mph have been reported.

Derechos in the United States are most common in the late spring and summer (May through August) and typically in two general areas. One reaches through the "corn belt" from the upper Mississippi Valley into the Ohio Valley. The other one stretches from the mid Mississippi Valley into the southern Plains. During the cool season (September through April) derechos can still occur from eastern Texas into the southeastern states.

Besides the United States, derechos have been reported in eastern Germany, Bangladesh and portions of India. (and, by the way, they can occur at the same time as tornadoes).

That's only the beginning of a very interesting topic, and for more information, take a look at this information from the Storm Prediction Center in Norman Oklahoma. http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm

Hopefully, you'll only get to study them from a distance

Wednesday, May 6, 2009

Partly cloudy partly sunny?

As you see the terms partly cloudy or partly sunny, have you ever wondered just what they mean? (Even some meteorologists do).


Here's a look at a few terms that you might find helpful.
Cloudy is when the sky is completely covered by clouds, with no view of blue sky.
Clear is when there are NO clouds in the sky.

Those were the easy ones, now it gets a little more interesting.

Mostly cloudy in a forecast means that most of the day will be cloud-covered. When used to describe current conditions, it means more than half of the sky is covered by clouds.
Partly cloudy When used in a forecast, it means that less than 1/2 of the day will be cloudy. For current conditions, it means that less than 1/2 of the sky is covered by clouds.
Partly sunny If you read this in a forecast, it means that more than half the day will be cloudy. If it's used to describe current conditions, it means that more than 1/2 of the sky will be covered by clouds.
Mostly sunny Not as simple as it sounds, but easily understandable. If you see this term in a forecast, it means that most of the day will be sunny. Used for current conditions, it means that most of the sky is clear.
There are some even more technical definitions (defining how many 8ths of the sky are covered by clouds) used by the National Weather Service, but for everyday use, the ones I listed above should be good to go.
Looking forward to seeing more of your questions!

Tuesday, May 5, 2009

Thunderstorm Safety

Since we'll be seeing more (particularly afternoon and evening) thunderstorms this month, here's a quick review of some of the terms and safety rules you need to keep in mind.

For every 5 seconds you can count between the lightning and the thunder, the lightning strike was 1 mile away.

The 30/30 rule advises that if you can count less than 30 seconds between the lightning strike and the rumble of thunder. Get to shelter and stay there until 30 minutes have gone by since the last thunder.

A SEVERE thunderstorm has one or all of the following characteristics...
1) Hail 1" in diameter or larger
2) Winds 58 mph or stronger
3) A tornado

A SEVERE THUNDERSTORM/TORNADO WATCH means that severe storms are possible in and close to the watch area. The elements are in place, and if they come together, severe weather could develop, so keep your eyes open. (These are issued by the Storm Prediction Center in Norman, Oklahoma).

A SEVERE THUNDERSTORM/TORNADO WARNING means that severe weather is imminent or already occurring. It's time to get to shelter...RIGHT NOW.

When severe weather strikes, you'll get the life-saving information you need from FirstAlert Doppler. It's really the only radar in southern Colorado that shows where the storms are right now, not 5 or 10 minutes ago, like the other radars you see on the air. (and wouldn't you really rather know where the storm IS, instead of where it WAS?).