The WSR-88D (Weather Surveillance Radar 1988 Design Doppler) was installed in extreme northeast Pueblo county (about 18 miles northeast of the WFO Pueblo office) in December 1994, and commissioned for official use the second week of August 1995. This location is probably the best for tracking both thunderstorms and snow events over our 21 county warning and forecast area.
While the Doppler radar obviously cannot see through the mountains, it can see storms well into the high country west of Colorado Springs, and can see the mid and high level structure of storms over the San Luis Valley and surrounding mountains. Therefore, where most of our severe weather occurs, in southeast Colorado east of the mountains, the Doppler radar has an unobstructed view of thunderstorms and lesser weather.
Reflectivity and velocity data is collected by the radar and transmitted via a high speed communications line to WFO Pueblo, where the data is processed and displayed. A trademark of the Doppler radar is its high power output, and therefore, its sensitivity. It can actually depict clouds, atmospheric aerosols (tiny particles in the air), and bugs in the air on the output screen. As a consequence, the radar shows cool air outflow boundaries from showers and thunderstorms, which can be tracked, and can initiate further thunderstorm development elsewhere in our area. Cold fronts can also be monitored on the radar as they plow through the area throughout the year. The Doppler's ability to detect wind speed and wind direction in storms, and throughout the general area, allows the staff to see anything from the beginnings of a tornado circulation in a thunderstorm, to the area wide upslope and downslope events that so profoundly influence our weather in southern Colorado.
The WSR-88D excels in detecting severe weather events that threaten life and property, such as large hail, damaging winds, tornadoes, and locally heavy, flooding rain. More importantly, this severe weather is seen by the Doppler radar more definitively than with the old conventional radar. By this we mean, the severe weather is often detected minutes quicker than with the old radar, and seen in a more specific area. Therefore, the warnings can be issued for a more specific area, lessening the false alarm rate for short-lived events such as hail, damaging winds, tornadoes, and flash floods, and you have more time to take cover.
For general information on how Doppler Radar works, see http://www.crh.noaa.gov/radar/radinfo/radinfo.html
From the northeast corner of Pueblo County, around 5,300 feet MSL, the Doppler radar sends out high-powered bursts of energy that travels near the speed of light throughout Colorado. When the energy hits a target in the atmosphere, it is reflected back to the radar. Through sophisticated computer technology, that information is displayed on a monitor that can be easily seen by the radar operator.
The mountains west of the Doppler radar are formidable barriers for the radar energy. In fact, the energy is blocked by the mountains at the lowest elevation scan angles of the radar. The Wet Mountains (the closest in the above photo), about 50 miles west of the radar, tower to around 12,500 feet MSL, or 7,000 feet above the radar. The far, snowcapped peaks are the Sangre de Cristo Mountains. They are 80 miles away from the radar, and range up to over 14,300 feet MSL, or 9,000 feet above radar level.
(Click image for larger view)
Between these two mountain ranges lies the Wet Mountain Valley. The radar can see the tops of rain and snow showers along and just below the peaks of the Sangre de Cristo Mountains.
Because of these two mountain ranges, precipitation in south central Colorado, in and around the San Luis Valley, can only be seen 9 to 10 thousand feet above ground level and higher. Important radar information is lost below these levels.
There is an abrupt rise in the terrain west of Colorado Springs, the Rampart Range. The highest terrain in this mountain range is the famous Pikes Peak, 14,115 feet MSL (seen on our homepage behind WFO Pueblo's building). Pikes Peak blocks the view of low level weather northwest of its summit in Teller county, because the radar is southeast of the grand mountain.
The Doppler radar has a couple of different products which help meteorologists to more easily assess whether a thunderstorm contains large hail. The Vertically Integrated Liquid (VIL) product has provided radar operators a quick way to determine the presence of large hail within a thunderstorm. Below is a VIL product.
The yellow, orange, and red colors usually indicate much rainfall and large hail. A severe thunderstorm warning can be issued by WFO Pueblo for that severe hail immediately, even BEFORE receiving reports from citizens in that area.
Another way the radar operator can look at a storm is with the cross-section product. This lets him/her look a slice of the storm from lower to higher heights. The image below shows a cross-section.
A severe storm will often have an extreme updraft, around 100 mph, which corkscrews up into the upper parts of the storm. This updraft can punch the majority of the raindrops and hail out of the updraft area, and throw them to areas all around the updraft core. In the image above, you can see this narrow core of lesser reflectivity, which shows the position of the extreme updraft. This narrow core of lesser reflectivity, surrounded by higher reflectivity (heavy rain and hail), is called a Bounded Weak Echo Region (BWER). It points to the extreme, twisting updraft with a very high probability of severe hail, damaging winds, and even a tornado in that area of the storm.
The Doppler radar helps the radar operator immensely in determining whether a thunderstorm contains damaging winds or even a tornado. On June 22, 1995 a thunderstorm developed near Palmer Lake in far northwest El Paso county. The storm split in half, one part moving north across the Palmer Divide, the other moving east southeast toward Black Forest and Falcon. The southern storm did not have high winds or severe hail for several minutes, but the Pueblo Doppler radar did show a suspicious shape in the reflectivity product shown below.
The storm had an extension, dipping southward on its western side, called a pendant. The radar was sounding alarms for rotation in the western part of the storm. The product below is the wind detection part of the radar.
It shows strong airflow toward the radar (green). On either side of the inbound (green) airflow, is strong airflow away from the radar (reds). Where the radar detects strong counterclockwise rotation, it prints out a yellow "donut", a mesocyclone. The clockwise rotation was weaker. The brief, narrow, but destructive tornado occurred at the yellow "donut" (mesocyclone) position seen in the above product.
When the Doppler radar detects a very narrow and intense circulation with a thunderstorm, a Tornado Vortex Signature (TVS) is displayed on the radar screen, as seen below as a red, upside down triangle.
Its appearance sometimes means a tornado circulation has already made it to the ground, or will shortly.
The Doppler radar has an algorithm (computer program) that attempts to estimate the amount of rain that has fallen across the area. This running total of rainfall allows WFO Pueblo to quickly assess the potential for flooding. We can often tell the difference between nuisance flooding and life-threatening flooding from the radar estimates. Often when radar rainfall estimates reach just over one inch an hour, the Pueblo office will issue an Urban/Small Stream Flood Advisory. This is nuisance or inconvenience flooding. When radar estimates reach three or four or more inches, it's usually wise to issue a Flash Flood Warning. Such was the case on a June night in northeast El Paso county. The image below shows the Storm Total Precipitation (STP) product late in the evening that night.
A nearly stationary strong thunderstorm dumped over five inches of rain in a two hour period. There was extensive flooding of the Black Squirrel Creek basin in eastern El Paso county. The above scenario is repeated nearly a dozen times a year in our County Warning Area.