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WSR-88D Doppler Radar
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.
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For general information on how Doppler Radar works, see
http://www.crh.noaa.gov/radar/radinfo/radinfo.html
![Radar and Mountains](/peth04/20041101110913im_/http://www.crh.noaa.gov/pub/images/rdr_mtn.jpg) |
Radar and the Mountains
From the northeast corner of Pueblo County, around 5,300 feet MSL, the
Doppler radar sends out high-powered bursts of energy that travel 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.
In the photo below, another range of mountains to the southwest
of the radar, the Spanish Peaks, blocks the energy of the lowest radar
scans as it heads out into far south central Colorado.
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Radar and Hail
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.
.![Cross Section Reflectivity](/peth04/20041101110913im_/http://www.crh.noaa.gov/pub/images/rhi_2.jpg)
A severe storm will often have an extreme updraft, around 100 mph,
that 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.
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Radar and Damaging Winds and Tornadoes
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.
![Reflectivity Hook Echo](/peth04/20041101110913im_/http://www.crh.noaa.gov/pub/images/falcn_r2.jpg)
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.
![Mesocyclone Image](/peth04/20041101110913im_/http://www.crh.noaa.gov/pub/images/falcn_v2.jpg)
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.
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Radar and Flooding
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.
![Storm Total Precipitation Image](/peth04/20041101110913im_/http://www.crh.noaa.gov/pub/images/stp_2.jpg)
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.
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Last Modified:
Monday, 15-Dec-2003 22:11:37 GMT
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