U.S. CitiesCity-Data Forum Index
Go Back   City-Data Forum > U.S. Forums > Colorado
 [Register]
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
View detailed profile (Advanced) or search
site with Google Custom Search

Search Forums  (Advanced)
Reply Start New Thread
 
Old 05-22-2012, 10:17 AM
 
8,317 posts, read 25,091,437 times
Reputation: 9065

Advertisements

Since this subject has come up numerous times in other posts and because the thunderstorm season (hopefully) is nearly upon us, I thought I would post a thread about Colorado’s thunderstorm climatology. Data presented here has been gathered from my many years of personal observation and extensive research of published technical papers on the subject. I actually plan to incorporate this into a book I’m working on about southern Colorado and northern New Mexico geography and climate. Maybe someday I’ll have time to finish it!

I will talk about three major aspects of Colorado thunderstorms: Precipitation, lightning, and distribution/frequency/severity. These observations are based on normals and averages over many years. Because of Colorado’s interior location and geography, there is considerable variation from year-to-year—so what is expected and “normal” may not be what actually occurs in any given year.

Thunderstorms require three major ingredients to form: moisture, atmospheric instability, and convection. Absent of one or more of these components, thunderstorm development will be impaired. During the summer months in Colorado, atmospheric instability and convection occur almost daily, thanks to daytime heating and the atmospheric instability triggered by Colorado’s mountainous geography. In Colorado, typically, the most limiting factor to thunderstorm development is the lack of atmospheric moisture in Colorado’s arid to semi-arid climate. Fortunately, the westward expansion of the Bermuda High during the spring and summer months brings regular “pulses” of moisture from the Gulf of Mexico and/or the Gulf of California into Colorado. Thus, when that moisture and the other factors of convection and atmospheric instability are present together in a location, thunderstorm development is likely.

Let’s talk about thunderstorm distribution, frequency, and severity first. All are affected by location, altitude, and local geography. June, July and August are the primary thunderstorm months in Colorado, with a “shoulder season” of May and September—those two “shoulder” months typically seeing thunderstorm activity usually limited to lower elevation areas. The distribution of thunderstorm activity varies considerably across Colorado. If one draws a rough line from approximately Douglas Pass northwest of Grand Junction southeastward through Palmer Lake on the summit of the Palmer Divide, thence southeastward to Kansas border, one would find that the most thunderstorm-prone months are in June to mid-July north of the line and mid-July to the end of August south of the line. The least thunderstorm-prone areas of Colorado are the lower western valleys, the San Luis Valley, and a “slot” north of Denver to around Greeley. (The Denver-Greeley location may see fewer thunderstorm events, but—unlike the western valleys and San Luis Valley—it can and does get very severe thunderstorms and hail periodically.) The most thunderstorm-prone areas of Colorado are along and immediately east of the Front Range from Palmer Lake southward to Colorado Springs, immediately east of the Wet Mountain range around Rye and San Isabel, and eastward of the Sangre de Cristo Range and south of the Spanish Peaks extending down the Purgatoire River valley to Trinidad and Raton Mesa. This latter thunderstorm “hot spot” extends southward into New Mexico eastward of the Sangre de Cristo Range to south of Las Vegas, New Mexico. In terms of thunderstorms days, the New Mexico portion of this thunderstorm area is the most thunderstorm-prone location in the United States outside of Florida. (The most thunderstorm-prone location in the US outside of Florida in terms of total hours of thunderstorm activity per year is located in eastern Kansas and western Missouri—encompassing the cities of Topeka and Kansas City.) All of these areas, all of which are essentially in the southern half of Colorado, typically see 50-60 thunderstorm days per year—almost all occurring from mid-June through August. Higher mountain areas of Colorado see around 40-60 thunderstorm days per year, with the highest frequency occurring in the San Juan mountains of southwest Colorado and the least in the northwest portion of Colorado mountains.

Typical thunderstorm activity west of the Front Range in Colorado is of relatively short duration and typically produces relatively low precipitation per storm—usually 0.25” of rain or less. As one moves east on Colorado’s Eastern Plains, thunderstorm severity and precipitation per storm increase. Any area east of the Front Range can see tornado development, but tornadic events are relatively rare in Colorado. Even more rare are severe tornados, but they can and do occur occasionally from the Front Range eastward. Severe hail (golfball size or larger) occurs nearly every summer in Colorado—“Hail Alley” extends eastward from the Front Range into southeastern Wyoming, western Nebraska, western Kansas, the Oklahoma Panhandle and the Texas Panhandle. Cheyenne, Wyoming—just north of the Colorado border—is considered the “Hail Capital” of the United States.

In the mountains, foothills, and deserts of Colorado, flash flooding can be a serious matter. While most Colorado thunderstorms are not big precipitation producers by Midwest or Eastern standards, even a thunderstorm producing only 1” of rain in a concentrated area may produce a serious flash-flood, thanks to Colorado’s steep topography and thin soils. If a severe storm with an ample moisture supply “parks” in single location and delivers copious amounts of rain, an epic flash flood can occur. An example of this was the 1976 Big Thompson Canyon flood west of Loveland that was one of the deadliest floods in US history.

Which brings us to thunderstorm development, timing, and movement in Colorado. When all three ingredients for thunderstorm development are available (moisture, atmospheric instability, and convection), thunderstorm development usually initiates when morning heating begins to destabilize the atmosphere. Then, local topography further may destabilize the atmosphere—and can both cause and enhance convection. This can easily be observed in the mountains. If ANY clouds are present by, say, around 8 AM (all times noted here are Mountain Daylight Time) on a summer morning in the Colorado mountains, that indicates that some moisture is available in the atmosphere and thunderstorms may be likely to form by early afternoon. Usually, by 10 AM, morning heating by the sun is sufficient to initiate convection and the morning’s small cumulus clouds will begin to grow. How large and how fast depends on how much convection there is and how much moisture is available. By around Noon to 1 PM, the cumulus clouds will have developed into the cumulonimbus clouds—the “thunderhead”—and rain will start to fall. Typically, the storms will move eastward on the prevailing westerly winds. Some days they may rapidly dissipate as the air cools and they exhaust their available moisture. On some days, however, they may plow into additional moisture as they move downward and eastward. When this happens, they may become much larger thunderstorms that move over lower elevations and they may become severe. In truly long-lived events, the outflow from these storms may continue to destabilize the atmosphere for hundreds of miles to the east, triggering storms as far east as the Mississippi Valley. This is one reason that peak thunderstorm activity in places like eastern Nebraska and Kansas typically occur from early evening well into the night, while thunderstorm activity in Colorado generally occurs much earlier in the day. The most common time for thunderstorm activity in Colorado is from around 1 PM to early evening, though variations can and do occur.

Ironically, it is the timing of thunderstorms in Colorado that makes Colorado have one of the highest rates of lightning fatalities in the United States. In terms of lightning strikes per storm event and lightning density per square mile, Colorado lags far behind most Midwestern states, many southern states and Florida. What makes Colorado storms so dangerous insofar as lightning is concerned is that most thunderstorms occur during the day when the most people are outside. Colorado’s topography is also such that it is very easy for people to be caught on “high spots” very prone to lightning strikes. Colorado storms also can develop very quickly, often with little warning to those unfamiliar with Colorado weather (i.e., tourists). The old mountaineer’s rule to “be off the mountain by Noon” is a very good one to follow.

The role of Colorado thunderstorms to the state’s ecology is important and generally beneficial. Much of Colorado’s summer rainfall is from thunderstorms. While summer rain is not a major source of water for streamflows, it is very important to keep soil moisture up and to keep plants green. Without it, Colorado’s mountain areas would be brown for most of the summer—and much more prone to forest fires. Colorado’s dryland crops on the Eastern Plains also rely on precipitation from thunderstorms for much of their summer water needs. The chemical reaction of lightning in the atmosphere also releases large amounts of nitrogen—an important plant nutrient—which then is carried to the ground by the rain. Even lightning’s propensity to start forest fires is a natural part of forest regeneration. Finally, there is just the joy one can have watching one of Nature’s great spectacles. A mountain thunderstorm can be a majestic event to enjoy—safely, of course.

A great source of Colorado thunderstorm information can be found at the Pueblo National Weather Service website:

NWS Pueblo, CO

Especially interesting is the "Severe Weather Climatology" page ( Severe Weather Climatology (Tornado, Hail > 1.00, Wind > 50 knts) for Southeast and South Central Colorado ) and the "Colorado Lightning Resource Page" ( NWS Pueblo Lightning Page ).

This technical paper is also a great resource: http://www.crh.noaa.gov/Image/pub/lt...climo_5sep.pdf

Many thanks to Steve Hodanish and the Pueblo NWS for making this information available on-line.

Last edited by jazzlover; 05-22-2012 at 10:35 AM..
Reply With Quote Quick reply to this message

 
Old 05-22-2012, 10:29 AM
 
Location: Western Colorado
10,518 posts, read 11,623,635 times
Reputation: 24167
Fascinating post jazz, thank you.

When I lived in Ridgway, it was funny how one could tell the time by seeing the thunderheads build over the San Juans.
Reply With Quote Quick reply to this message
 
Old 05-22-2012, 12:26 PM
 
1,375 posts, read 2,618,882 times
Reputation: 1663
Nice post!

Why are Colo thunderstorms prone to hail development?
Reply With Quote Quick reply to this message
 
Old 05-22-2012, 12:51 PM
 
8,317 posts, read 25,091,437 times
Reputation: 9065
Quote:
Originally Posted by BarryK123 View Post
Nice post!

Why are Colo thunderstorms prone to hail development?
The combination of Colorado's high altitude, which means that colder air is closer to the ground (falling hail does not melt down as much as lower elevation areas where it falls through a thicker layer of hotter air), and because of the strong convection currents found in severe Colorado thunderstorms, that cause the hail to rise and fall repeatedly within the thunderstorm (gathering more water to freeze on the hailstone with each trip up through the cloud) before finally achieving sufficient mass to overcome the storm's strong updraft and fall to the ground.
Reply With Quote Quick reply to this message
 
Old 05-22-2012, 01:28 PM
R2F
 
26 posts, read 70,444 times
Reputation: 28
Very interesting read. I used to love watching the storms roll in off the mountains. I never really encountered the hail issue though, so that might be an interesting surprise for me when I get there.
Reply With Quote Quick reply to this message
 
Old 05-22-2012, 02:02 PM
 
41 posts, read 222,867 times
Reputation: 33
Interesting, I grew up out on the northeastern plains of Colorado, so I'm familiar with severe weather during these times. I've always wondered why places along I-70 (Limon, Burlington, etc), tend to get hammered more with severe weather, and this explains it.
Reply With Quote Quick reply to this message
 
Old 05-22-2012, 03:19 PM
 
8,317 posts, read 25,091,437 times
Reputation: 9065
Quote:
Originally Posted by bco24 View Post
Interesting, I grew up out on the northeastern plains of Colorado, so I'm familiar with severe weather during these times. I've always wondered why places along I-70 (Limon, Burlington, etc), tend to get hammered more with severe weather, and this explains it.
If one looks at the topography, the area south of Limon is actually fairly high altitude for the Eastern Plains. A lot of storms rolling off of the very thunderstorm-prone Palmer Divide follow that high area as they move east. By the time those storms get to low elevation places like Burlington to the east, they are strong storms that frequently are plowing into relatively moist air streaming north from the Gulf of Mexico. That can set the stage for some wild weather.
Reply With Quote Quick reply to this message
 
Old 05-22-2012, 03:50 PM
 
Location: Pueblo - Colorado's Second City
12,099 posts, read 20,344,698 times
Reputation: 4125
I love thunderstorms. The lighting and rain even hail is pretty to look at. Pueblo had our first major thunderstorm with hail the other night. I posted pictures in the Pueblo weather thread. It was a fun storm with little damage the kind of storm I really like to see. I hope we get a lot of them this summer.
Reply With Quote Quick reply to this message
 
Old 05-22-2012, 04:03 PM
 
8,317 posts, read 25,091,437 times
Reputation: 9065
Quote:
Originally Posted by Josseppie View Post
I love thunderstorms. The lighting and rain even hail is pretty to look at. Pueblo had our first major thunderstorm with hail the other night. I posted pictures in the Pueblo weather thread. It was a fun storm with little damage the kind of storm I really like to see. I hope we get a lot of them this summer.
Well, Pueblo actually has one of the lower average frequencies of thunderstorm days on the Front Range, while Colorado Springs to the north is the champ.

Here is the tally for cities along the Front Range:

Colorado Springs 51-59 thunderstorm days per year, depending on the weather station cited. Palmer Lake, at the top of the Palmer Divide, by some unofficial counts, gets 65-70 thunderstorm days on average.

Denver 40.

Pueblo 40

Fort Collins 40-45 (this figure is unofficial, as many non-NWS weather stations do not track thunderstorm days, and Fort Collins, despite being home to the State Climatologist's office, is not an official NWS weather site).

Cheyenne, Wyoming (just 12 miles north of the Colorado border) 52 thunderstorm days.
Reply With Quote Quick reply to this message
 
Old 05-22-2012, 04:22 PM
 
Location: Pueblo - Colorado's Second City
12,099 posts, read 20,344,698 times
Reputation: 4125
^

40 thunderstorm days is a lot for a city that is really just a step above a dessert and I can always count on a few of them to be severe like the one a few nights ago but not like the ones they get in the plains that is just scarey. Overall I think Colorado has the best climate in the nation and the world and that is one reason why I love it here so much.
Reply With Quote Quick reply to this message
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.

Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.


Reply
Please update this thread with any new information or opinions. This open thread is still read by thousands of people, so we encourage all additional points of view.

Quick Reply
Message:


Options
X
Data:
Loading data...
Based on 2000-2016 data
Loading data...

123
Hide US histogram


Over $104,000 in prizes was already given out to active posters on our forum and additional giveaways are planned!

Go Back   City-Data Forum > U.S. Forums > Colorado
Follow City-Data.com founder on our Forum or

All times are GMT -6.

© 2005-2018, Advameg, Inc.

City-Data.com - Archive 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35 - Top