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Featured Articles

These are examples of CSU-CHILL data selected from meteorologically interesting cases. The data plots generally have had some basic level of post-processing applied (i.e., calculations of derived fields, utilization of specialized base maps, etc.)

Breaking lee waves: 9 January 2017.
Wave patterns downstream of the Rocky Mountains were observed in a series of S-band RHI scans conducted during a high wind event. These patterns suggest the breakdown of a standing lee wave flow.
Cold frontal passage at the CSU campus weather station: 7 December 2016.
CSU-CHILL radial velocity data collected in a series of RHI scans indicated that a low level wind direction change took place at the weather station located on the main CSU campus during a frontal passage. Surface data collected at this station confirm that a cold frontal passage accompanied by several inches of snow occurred during the time period when an echo band passed the campus station.
Varying thunderstorm Zdr patterns: 13 June 2016.
Low altitude Zdr signatures vary in two thunderstorms captured in the same RHI sweep.
Cold frontal passage: 23 September 2016.
A strong cold front passed the CSU-CHILL radar site during the afternoon hours of 23 September 2016. The X-band RHI scan data showed well-defined differences between the dual polarization characteristics in a light rain shower just ahead of the front vs. the dust-laden boundary layer air behind the front. The S-band RHI data documented billow structures near the upper surface of the cold airmass.
Thunderstorm outflow boundary: 1 July 2016.
A line of storms passing to the north of CSU-CHILL generated an outflow boundary. This boundary was associated with a fine line echo. The development and movement of the fine line echo was documented in animation loops prepared from low elevation angle surveillance scans.
Severe thunderstorm activity near CSU-CHILL: 29 July 2016.
Selected digital photographs and dual polarization radar data are presented from a hail-producing thunderstorm that affected the immediate vicinity of the radar during the early evening hours of Friday, 29 July 2016 (date based on local time zone).
Thunderstorm passage over a severe weather spotter site: 30 June 2016.
Low elevation angle PPI sector scans were made at one minute intervals while a thunderstorm deposited 1.2 inches of rain in 20 minutes according to a severe weather spotter.
Tornadic supercell thunderstorm on 7 May 2016: Dual polarization parameters and their evolution.
CSU-CHILL scans through a severe thunderstorm contained dual polarization signatures associated with precipitation, biological, and debris targets.
Tornadic supercell thunderstorm: 7 May 2016
A confirmed tornado affected the Empire Reservoir area (~45 km ESE of CSU-CHILL) on 7 May 2016. The horizontal wind field in the low-level mesocyclone has been synthesized from the radial velocities observed by the CSU-CHILL and NWS KFTG radars.
Zdr regimes in echoes from insects and raindrops: 1 July 2015
The echoes in a series of low elevation angle PPI scans on a summer afternoon were initially dominated by the highly positive Zdr values associated with insects. Where developing rain shafts penetrated into the insect-laden boundary layer, the more modest positive Zdr levels produced by oblate raindrops appeared.
Variations in snow crystal riming and Zdr: 26 - 27 November 2015
Based on hydrometeor-observing instrumentation installed at the Easton Airport for the MASCRAD project, periods of positive (> ~ +2 dB) Zdr observed by the CSU-CHILL X-band system were found to be associated with pristine, minimally rimed stellar ice crystals.
Zdr and phidp variations in a developing rain shaft: 10 August 2015
A sequence of low elevation PPI scans through a developing thunderstorm rain shaft indicated that enhanced positive Zdr values developed a few minutes before the phidp accumulations became significant. Drop size sorting probably reduced the concentrations of small drops during the initial high Zdr / low phidp time period.
RhoHV observations in a developing hailstorm: 16 August 2015
The dual polarization characteristics of a developing hailstorm were observed in a continuous series of 1.5 degree elevation angle PPI scans. Areas of locally reduced RhoHV values were observed in association with the high reflectivity and near 0 dB Zdr regions that are indicative of hail.
Snow band observations: 17 November 2015
A snow band associated with the deformation region of a developing surface low pressure system was observed to the southeast of the CSU CHILL radar during the predawn hours of 17 November 2015. Due to the strong horizontal wind fields, the snow reached the ground ~40 km downwind of its apparent growth region aloft.
Strong attenuation and differential attenuation at X-Band: 14 July 2015
A thunderstorm located ~20 km east of the CSU-CHILL radar produced a brief pulse of heavy rain during the afternoon hours of 14 July 2015. A sequence of 1.5 degree elevation angle PPI scans showed increased attenuation and differential attenuation effects as the rain rate increased.
Dual-polarization radar indications of ice crystal canting due to electric fields: 5 June 2015
Both the NWS KFTG and CSU-CHILL radars detected indications that enhanced electric field strength in the upper levels of a thunderstorm were re-orienting planar ice crystals towards a more vertical alignment. Data from the Northern Colorado Lightning Mapping Array (LMA) confirmed that lightning discharges occurred near these re-oriented crystal areas.
Overshooting thunderstorm top: 4 June 2015
The CSU-CHILL radar made several RHI scans through a severe thunderstorm with an overshooting cloud top. Additional views of the storm's upper level structure are provided by data from the NWS KFTG radar and the GOES East satellite.
Microburst winds and melting hail at the Easton Airport field site: 9 July 2015
High time resolution low elevation angle PPI scans were made as a thunderstorm developed over the ground instrumentation site that was established at the Easton Valley View Airport for the MASCRAD project. Time lapse loops of the radial velocity data show the development of a microburst as the thunderstorm matured. Hydrometeor images recorded by the 2D video disdrometer at Easton indicated that the storm generated melting graupel / small hailstones at the surface.
Thunderstorm cell initiations: 11 June 2015
A propagating fine line echo triggered the development of several thunderstorms that produced locally heavy rain in the vicinity of Loveland, Colorado during the afternoon of 11 June 2015. Animated image loops generated from low elevation angle PPI scans show the development of the these thunderstorms.
Onset of dual polarization hail indications: 30 April 2015
The low levels of an isolated thunderstorm were observed through a continuous series of single-elevation angle (1.5 deg) PPI scans. Hail development in the echo core, as evidenced by a reduction in differential reflectivity and an increase in linear depolarization ratio, was documented in a series of image loops.
Evolution of boundary layer echoes: 27 March 2015
Northwesterly surface winds increased at the CSU-CHILL radar site in association with the passage of a linear echo feature in the boundary layer clear air echo pattern. A series of continuous RHI scans done along the axis of this linear echo feature captured the evolution of a number of cumulus cloud related Bragg echo features.
High time resolution observations of a heavy rain area: 3 August 2013
The CSU-CHILL radar conducted a series of continuous 1.7 degree elevation angle 360 surveilance scans of an area of thunderstorms that were producing heavy rain fall just east of the radar site on 3 August 2013. Animations of the approximately one minute time interval reflectivity and radial images show the rapid evolution of the echo features.
Snapshot dual-Doppler and LMA observations of a convective line: 27 June 2014
The starting times of volume scans conducted by the CSU-CHILL and NWS KFTG radars fell into synchronization at 2212 UTC on 27 June 2014 while a line of thunderstorms was located to the east of the radars. Three dimensional wind fields obtained from a dual-Doppler synthesis have been combined with Lightning Mapping Array (LMA) VHF radiation source locations for this volume scan.
X-band radar observations in widespread snow: 31 January 2014
The low level radial velocity pattern indicated an increase in the upslope flow component during a 3 hour time interval in the lifetime of an overnight snow storm.
Initial Multiple Angle Snow Camera-Radar experiment (MASCRAD) project operations: 15 November 2014
Example data collected by the MASC camera system and the CSU-CHILL radar during a period of moderate snow on 15 November 2014 is presented.
Dual-Doppler analysis of low-level winds in a thunderstorm complex: 27 August 2014
The horizontal wind field at 2.4 km MSL in an analysis area containing a thunderstorm complex was synthesized from data collected by the CSU-CHILL and NWS KFTG radars. A fine line echo was present along the boundary between the thunderstorm outflow and the ambient boundary layer winds.
Cold frontal passage at the CSU-CHILL radar site: 1 October 2014
Surface winds abruptly changed direction and increased in speed as a cold front passed the radar site during the afternoon hours of 1 October 2014. The reflectivity and radial velocity patterns observed in a series of low elevation angle surveillance scans underwent significant evolution during the frontal passage.
Passage of a high Kdp area over a tipping bucket rain gauge: 25 August 2014
A small area of S-band one-way specific differential propagtion phase values of ~5 deg / km crossed a tipping bucket rain gauge operated by the Denver Urban Drainage and Flood Control District on 25 August 2014. Time histories of the CSU-CHILL reflectivity and Kdp data at the gauge location have been compared to the bucket tip times recorded by the gauge.
Surface divergence and heavy rainfall beneath a thunderstorm: 19 June 2014
An intense thunderstorm passed just south of the CSU-CHILL radar during the early UTC hours of 19 June 2014. A dual-Doppler horizontal wind synthesis confirmed that low-level divergence was associated the the storm's visually opaque heavy rain shaft.
Dual polarization hail signatures observed by the CSU-CHILL and the NWS KCYS radars: 23 June 2014
A location where severe weather spotters were reporting 1.5 inch diameter hail was scanned by both the CSU-CHILL and NWS KCYS radars during the afternoon of 23 June 2014. Various dual polarization indications of hail were observed in the RHI scan data collected by CSU-CHILL and in the conventional PPI scan data collected by KCYS.
Boundary layer outflow wind patterns on several different size scales: 11 June 2014
During the mid-day hours of 11 June 2014, outflows from convective showers in the vicinity of the CSU-CHILL radar produced radial velocity patterns in the boundary layer that ranged from a gust front with a length of ~50 km to a microburst on a scale of ~5 km. While this activity was in progress, the CSU-CHILL radar collected 0.75 degree elevation angle PPI scans that updated every ~1.25 minutes. Time lapse loops of the resultant sequences of reflectivity and radial velocity images have been prepared.
Mesocyclone observed in the FRONT network by the NCAR S-POL and CSU-CHILL radars: 21 May 2014
Prof. Sandra Yuter (North Carolina State University) is conducting the NSF-sponsored ROSE (Radar Observations of Storms for Education) project using the FRONT (Front Range Observational Network Testbed) facilities during the 20 May - 20 June 2014 period. On 21 May, the CSU-CHILL and NCAR S-Pol radars were conducting time-synchronized volume scans for the ROSE project while a supercell thunderstorm developed near the Denver International Airport. Plots of the low altitude dual Doppler horizontal wind field and selected S-Pol dual polarization fields have been prepared.
Dual polarization signatures of melting hydrometeors: 23 August 2013
A CSU-CHILL RHI scan intercepted areas of both convective and stratiform precipitation during the early UTC hours of 23 August 2013. In the stratiform region where fairly homogeneous, light precipitation was occurring, the effects of hydrometeor melting produced a bright band. The melting process was more protracted for the larger diameter hydrometeors in the convective precipitation, causing the polarimetric melting signatures to occur closer to the ground.
Dual-Doppler mesocyclone observations: 20 July 2013
A low altitude mesocyclone developed near Aurora, CO, a location where horizontal winds could be synthesized from the radial velocity measurements made by the CSU-CHILL X-band radar and the operational NWS KFTG radar. The narrow (0.3 deg) beam width developed by the CHILL X-band system permitted high resolution observations to be made at ranges of 80 - 90 km.
Dual polarization hail signature development at low elevation angles: 27 July 2013
PPI scans at an elevation angle of 0.5 degrees were conducted as reflectivity rapidly intensified beneath a thunderstorm. Decreases in differential reflectivity (Zdr) and co-polar HV correlation coefficient (rhoHV) indicated that hailstones composed an increasing fraction of the intensifying precipitation core.
High Kdp values observed by the CSU-CHILL and KFTG radars: 21 July 2013
The lower levels of a thunderstorm that was producing intense rainfall were jointly observed by the CSU-CHILL and NWS KFTG dual polarization radars on 21 July 2013. One-way specific propagation differential phase (Kdp) magnitudes of ~8 deg / km were documented by both radars.
Thunderstorm passage over a tipping bucket rain gauge: 4 September 2013
Rain rates of ~60mm per hour were recorded by a Denver flood control district rain gauge during a thunderstorm passage on 4 September 2013. The CSU-CHILL radar made low elevation angle PPI sweeps at roughly one minute time intervals as the echo core passed the gauge. Time histories of the S-band reflectivity and specific propagation differential phase data at the gauge's azimuth / range location have been prepared.
Cell intensification following a boundary passage: 30 August 2013
Brief intensification was observed when fine line echoes in the boundary layer interacted with a small, pre-existing thunderstorm. Animations of the X-band dual-polarization data show evidence of higher concentrations of oblate rain drops during the intensification period.
S and X-band rhoHV observations in hail: 3 August 2013
Dual frequency data was collected during a hailstorm that affected the Greeley area on 3 August 2013. Indications of X-band rhoHV reductions due to Mie scattering effects appear to be present at a location of confirmed hail damage.
Initial plots from flooding rainfall in Aurora, Colorado: 13 September 2013
Preliminary plots of the CSU-CHILL dual-polarization data collected during a small time segment of a widespread flooding event have been developed.
An RHI scan sequence through thunderstorm outflow: 27 July 2013
The approach and passage of a thunderstorm gust front at the CSU-CHILL radar site was observed through a series of RHI scans that repeated at ~1 minute time intervals. Time lapse loops of the 3 GHZ (S-band) reflectivity and radial velocity data have been prepared.
Attenuation observed at 9 GHz (X-band): 15 July 2013
The X-band attenuation due to a thunderstorm's heavy rainfall core prevented the detection of more distant echoes. The evolution of the attenuation "shadow" is shown using selected time lapse loops.
Dual-Doppler observations of a Bounded Weak Echo Region (BWER): 17 June 2013
Synchronized dual Doppler scanning was done by the CSU-CHILL and Pawnee radars during a 20hr project on thunderstorm electrification. A storm observed on 17 June 2013 contained a Bounded Weak Echo Region (BWER) in association with the main updraft.
Time variations in bright band height: 12 April 2013
RHI sweeps were repeated at time intervals of ~47 seconds as an area of weakening rain showers approached the CSU-CHILL radar on 12 April 2013. (The radar was operating in X-Band only configuration). Fluctuations in the height of the Zdr bright band were noted as various localized reflectivity maxima descended through the melting level.
Selected dual-Doppler observations of a snow band: 15 April 2013
A well-defined snow band extended across the greater Denver area during the morning hours of 15 April 2013; portions of this band were located within the eastern lobe of the dual-Doppler domain defined by the CSU-CHILL and NWS KFTG radars. Example plots of the synthesized wind fields along with X-band polarimetric data from CSU-CHILL have been prepared.
High time resolution RHI's through a snow band: 4 March 2013
RHI scans repeated at ~1 minute intervals were done as a snow band approached the CSU-CHILL radar site. Small scale convective elements were observed in the upper portions of the echo system.
Dual frequency observations of a dry cold front: 15 August 2012
The fine line echo associated with a dry cold frontal passage at the CSU-CHILL radar site was observed at radar frequencies of both 3 and 10 GHz (S and X-Bands). The narrower X-Band beam provided a better resolution of small scale structures along the frontal echo.
Selected dual polarization observations in a supercell thunderstorm: 8 June 2012
A weakening supercell thunderstorm approached the CSU-CHILL radar site on the evening of 7 June 2012 (local date) during DC3 project operations. RHI scans were taken through the weak echo region (WER) and the adjacent hail shaft.
Dual wavelength hail detection: 26 September 2012
Systematic differences between the reflectivities observed at wavelengths of 11 and 3 cm were used to identify an area of hail on 26 September 2012. Supporting plots of the 11 cm wavelength differential reflectivity (Zdr) and hail differential reflectivity (Hdr) have been generated.
A comparison of dual polarization KFTG and CSU-CHILL Kdp fields: 26 September 2012
The Denver / Front Range WSR-88D radar was upgraded to dual polarization configuration in early September, 2012. During the afternoon hours of 26 September 2012, thunderstorms producing intense rain rates and sub-severe diameter hail moved through the Platteville, Colorado area. Plots of the Kdp fields observed in the Platteville storm by the KFTG and CSU-CHILL radars have been prepared.
Cold frontal passage: 3 October 2012
A strong, essentially dry cold front passed the CSU-CHILL radar site near 2200 UTC on 3 October 2012. The progression of the fine line echo and wind shift associated with front is shown in a time lapse of low elevation angle PPI scans.
Varying outflow boundary motion: 11 September 2012
Shower activity locally modified the motion of a pre-existing outflow boundary. The evolution of the boundary's motion is shown with a time lapse sequence of low elevation angle PPI images.
X-Band attenuation example: 30 July 2012
Regions of both stratiform and convective rain were observed during dual frequency test operations on 30 July 2012. Complete attenuation of the X-band / 3 cm wavelength signal occurred in an area of thunderstorm precipitation.
Initial dual frequency observations of rain: 17 July 2012
The CSU-CHILL dual frequency feedhorn was reinstalled on 5 July 2012. Preliminary plots of convective rain observed simultaneously at wavelengths of 11 and 3 cm have been prepared.
Anvil level dual Doppler horizontal winds: 15 June 2012
Winds synthesized from a dual Doppler volume scan done by the CSU-CHILL and Pawnee radars during the DC3 project are presented.
Thunderstorm outflow and rainfall near the surface over Ft. Collins: 1 August 2011
Radial velocity patterns and a rainfall time history plot are presented.
Time lapse imagery of sky conditions near the Hewlett fire on 16 May 2012
Digital camera images at one minute time intervals between 2020 and 2149 UTC taken from the CSU-CHILL radar site.
Bounded weak echo region (BWER) example: 9 June 2011
A marginally severe thunderstorm was observed with both PPI and RHI scans during the early UTC hours of 9 June 2011. Plots of the storm's three-dimensional structure have been generated.
Damaging hailstorm at Cheyenne, WY: 12 July 2011
A series of low elevation angle dual-polarization PPI scans were recorded by the CSU-CHILL radar as a severe hailstorm struck Cheyenne, WY. Time lapse loops of several radar data fields have been prepared.
X-Band Kdp observations in a snowstorm: 3 February 2012
Selected plots from dual frequency test operations conducted during a widespread snowstorm have been collected.
Initial CSU-CHILL X-band operations: January 2012
Example plots from test operations conducted with the dual frequency feed horn are presented.
Thundersnow: 14 November 2009
An echo line developed in association with a convergence zone generated by a westerly wind surge. This echo line produced observations of both snow and lightning at Denver International Airport. Locally reduced rhoHV and enhanced Ldr values were observed near the surface in the convective echo cores.
Cold air surge at the surface: 2 November 2011
A series of RHI scans were taken after a cold frontal passage. The increasing northerly surface winds following this frontal passage can be seen in a sequence of radial velocity images.
Differential attenuation patterns: 19 August 2011
Thunderstorm precipitation produced an axis of heavy rain that became radially-aligned with the CSU-CHILL radar. Differential attenuation along beam paths through this heavy rain caused a negative Zdr bias.
Fine line passage at Denver International Airport: 30 August 2011
The passage of a fine line echo coincided with the timing of a wind direction shift reported in the surface weather observations.
Time lapse observations of outflow phenomena: 11 August 2011
The low-level outflow patterns generated by rainshowers and weak thunderstorms are shown by animations of CHILL PPI plots and digital camera images.
Damaging hailstorm at Denver International Airport: 13 July 2011
Hail damage was inflicted on multiple aircraft at Denver International Airport during the evening hours of 13 July 2011. Selected CSU-CHILL dual-polarization data images from this storm have been generated.
Polarimetric radar identification of frozen hydrometeors in thunderstorm precipitation: 6 August 2010
The radar characteristics of individual range gates are used to place thunderstorm precipitation into one of three categories: (1) primarily rain; (2) mixed rain and hail; and (3) primarily hail. The areal coverage of these categories varies with time during a series of low elevation angle PPI sweeps through a thunderstorm.
Evolution of radial velocity and rain rate fields in low elevation PPI sweeps of a thunderstorm: 30 July 2010
A series of 1.5 degree elevation angle PPI scans document intensifying outflow and increasing rain rates as a storm reaches the CSU-CHILL radar site.
An RHI scan through a severe thunderstorm: 21 June 2010
A single RHI sweep through a severe thunderstorm reveals several signatures in the radial velocity and dual-polarization data fields.

More Featured Articles

Technical Notes

These articles deal with engineering topics of interest to users of CSU-CHILL data.

Using Time-series data from CSU-CHILL (TN-009)
Short article describing the time-series data extraction tool
X-band Solid State Transmitter Monitor User's Guide (TN-008)
User's Guide to the solid-state X-band transmitter monitor developed at CSU-CHILL.
Clock Generator User's Guide (TN-007)
User's Guide to the programmable clock-generator design developed at CSU-CHILL.
Frequency Synthesizer User's Guide (TN-006)
User's Guide to the programmable Frequency Synthesizer design developed at CSU-CHILL.
Radar Echoes from Wind Turbines (TN-004)
Wind Turbines have become increasingly common in recent years. Their Doppler spectral characteristics are presented, along with an animation showing the repetitive patterns present in the turbine spectra. An audio presentation of the same data is also available, clearly showing the temporal variation of the echo. A brief discussion on the effects of wind turbine proliferation on radar meteorology is also presented.
Coherent Leakage (TN-003)
This is a short discussion on coherent leakage, discussing the various causes of coherent leakage in weather radar receivers. Some troubleshooting tips are also provided.

More Technical Notes

Recent Observations

More Recent Observations articles

Ongoing Data Analysis

More Ongoing Data Analysis articles


The CSU-CHILL Casebook contains summaries of CHILL operations, categorized by keywords, project names and by date of operation.

Casebook Archives