Sunday, 13 June 1999

Sunday, 13 June 1999 Julian Day 164 Meteorological Summary A cold front moved in over night, cooling the air at low levels. Warming aloft occurred and stabilized the air in mid-levels, suppressing convective activity for the day. Operations Summary Sunday was a down day. Also, the Convair was down with an oil cooler leak. We did have some good discussions about how to make the operations a little more efficient and where further data gathering efforts should be concentrated. In general, it was felt that more high altitude data were needed, but only the Sabreliner could provide that. Also, it would be useful to get better measurements of the vertical structure of the storm, so that 5 kft. altitude separations may be attempted, if ATC agrees. Also if one of the aircraft could measure cloud base that would be useful for later analyses. More dual Doppler coverage at the expense of surveillance scans is probably in order. The pilots were also going to try to give ATC a little more warning about when and where they would be going up, to help alleviate some of the ATC problems we ve been having. 83

Data Type Source Aircraft T-28 Convair Sabreliner Ground CHILL Radars Pawnee NEXRAD Denver, CO NIDS data Cheyenne, WY (gif images) Grand Junction, CO Goodland, KS Upper Air Mobile CLASS Denver, CO Grand Junction, CO North Platte, NE Riverton, WY Dodge City, KS Profiler Platteville, CO Granada, CO CSU CHILL, CO Haviland, KS Hillsboro, KS Neodesha, KS McCook, NE Neligh, NE Fairbury, NE Merrinon, NE Medicine Bow, WY Goes 8 Denver (jpeg image) National METAR PIREPS Airmets Colorado Wyoming Nebraska Kansas U.S.A. U.S.A. Convective U.S.A. Sigmets Local Colorado Storm Wyoming Reports Nebraska Kansas Severe Rpts U.S.A. 13 June 1999 - Hourly Collection of Data Time (UTC) 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 84

13 June surface analysis not available 13 June 500 mb analysis not available 85 13 June 500 mb analysis not available

Denver, CO 13 June 1999 1200 UTC CHILL Radar 13 June 1999 1815 UTC 86

Monday, 14 June 1999 Julian Day 165 Meteorological Summary Monday turned out to be a very good day for multi-cell convection. Radar echo was observed over the mountains early in the day, and later a line propagated through the plains just north of CHILL, which became the target storms. Operations Summary The Convair was still down with an oil cooler problem, so only the T28 and the Sabreliner were available for this day. It was decided not to fly in formation today, but to treat each aircraft as separate flights. Sometimes the aircraft were flying within the same cell, and other times the aircraft were flying on different cells. The penetrations runs by the Sabreliner were designated Flight 9, by the T28 Flight 10. Both aircraft were off the ground by about 2030 UTC. Initial targets were two developing areas along a line each containing what appeared to be two cells. Cloud base at this time was about 15 kft. Flight 9 (Sabreliner) run 1 was through a developing system about 120 km north of CHILL at 27 kft., 205335-205613 UTC. At about the same time Flight 10 (T28) Run 1 was executed at 20 kft. from south to north through a developing line centered about 20 km north of CHILL, and encountered severe turbulence. The T28 then turned around flying north to south through the same storm at 21 kft.; 2100-2109. The Sabreliner was executing Run 2 from the north to the south through this system at 29 kft. from 2102-2104. Turbulence reported as light chop with some rain. This system was evolving rapidly, and both aircraft lined up for Runs 3 and 4 as north-south passes on either the west or east sides of the line. The Sabreliner was at 29 kft. for Run 3, at 33 kft. for Run 4, and the T28 at 21 kft. for both runs. Times of penetration were Flight 9 (Sabreliner) Run 3: 2113-2121, and Run 4: 2129-2133; Flight 10 (T28) Run 3: 2112-2119, and Run 4: 2120-2127. Both aircraft reported light to moderate turbulence during these runs. Because a new storm was developing to the east of this line, the T28 was vectored to do a west to east penetration of this new cell. Flight 10 (T28) Run 5 was executed 2136-2142; and reported a good bump at the updraft boundary. The Sabreliner meanwhile did another pass through the evolving line (which by this time contained three distinct cells) through the center line of the storm at a heading of about 130 deg and at an altitude of 30 kft. Light to moderate turbulence reported on this Flight 9 Run 5 between 2139-?. Flight 10 (T28) Run 6 was executed by turning the T28 around to do a westbound penetration between 2146-2158; with no turbulence experienced. That was the last run for the T28. The Sabreliner made 3 more runs through the new line to the east. Run 6 was northbound through this line which now contained 2-3 cells at 28 kft. from 2151-2157. For this run, the aircraft was guided through regions of the storm that showed little echo, but good CHILL-derived Doppler radial shears and elevated spectrum widths. The aircraft indeed experienced severe turbulence (pilot reported 300 ft. altitude excursion and 20-30 kt. airspeed excursion). Run 7 was a turn 87

around now southbound at about 150 deg heading through the same storm at 27 kft. at 2203-2209, before diverting out to the east. Only light turbulence and rain reported. Run 8 was initiated by turning around again northbound on the east side of the storm, still at 27 kft. from 2210-2214. Again the aircraft encountered moderate-severe turbulence while within green echo (rain, a little ice reported) in an area where the CHILL-derived spectrum widths were large. This was the last run of the day. Unfortunately the Sabreliner took a lightning hit on one of these runs, but the damage was minor. The position of these storms allowed most of the runs to be performed under dual Doppler coverage. Two radiosondes were launched, one at CHILL at 1800 UTC and the other to the south of CHILL at 2323. CHILL reflectivity at 4.04 degrees elevation. The scan time is 213230 UTC on 14 june 1999 and corresponds to Run 4 of Flight 9. The positions of the T-28 and the Sabreliner are shown as before. 88

Data Type Source Aircraft T-28 Convair Sabreliner Ground CHILL Radars Pawnee NEXRAD NIDS data (gif images) Upper Air Profiler Denver, CO Cheyenne, WY Grand Junction, CO Goodland, KS Mobile CLASS Denver, CO Grand Junction, CO North Platte, NE Riverton, WY Dodge City, KS Platteville, CO Granada, CO Greeley, CO Haviland, KS Hillsboro, KS Neodesha, KS McCook, NE Neligh, NE Fairbury, NE Merrinon, NE Medicine Bow, WY Goes 8 Denver (jpeg image) National METAR PIREPS Airmets Colorado Wyoming Nebraska Kansas U.S.A. U.S.A. Convective U.S.A. Sigmets Local Colorado Storm Wyoming Reports Nebraska Kansas Severe Rpts U.S.A. 14 June 1999 - Hourly Collection of Data Time (UTC) 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 89

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Denver, CO 14 June 1999 1200 UTC CHILL Radar 14 June 1999 1826 UTC 91

Tuesday, 15 June 1999 Julian Day 166 Meteorological Summary Cool, moist, upslope conditions in northeastern Colorado led to stable air and no opportunities for convection in the area. Operations Summary Down day. No CLASS balloons launched. 92

Data Type Source Aircraft T-28 Convair Sabreliner Ground CHILL Radars Pawnee NEXRAD Denver, CO NIDS data Cheyenne, WY (gif images) Grand Junction, CO Goodland, KS Upper Air Mobile CLASS Denver, CO Grand Junction, CO North Platte, NE Riverton, WY Dodge City, KS Profiler Platteville, CO Granada, CO CSU CHILL, CO Haviland, KS Hillsboro, KS Neodesha, KS McCook, NE Neligh, NE Fairbury, NE Merrinon, NE Medicine Bow, WY Goes 8 Denver (jpeg image) National METAR PIREPS Airmets Colorado Wyoming Nebraska Kansas U.S.A. U.S.A. Convective U.S.A. Sigmets Local Colorado Storm Wyoming Reports Nebraska Kansas Severe Rpts U.S.A. 15 June 1999 - Hourly Collection of Data Time (UTC) 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 93

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Denver, CO 15 June 1999 1200 UTC No CLASS soundings taken on 15 June 95

Wednesday, 16 June 1999 Julian Day 167 Meteorological Summary Upslope conditions continue. Outlook: Tomorrow looks a little better. Operations Summary A down day was called. A sounding was launched near Cheyenne, WY at about 1900 UTC. The sounding confirmed the stability. 96

Data Type Source Aircraft T-28 Convair Sabreliner Ground CHILL Radars Pawnee NEXRAD Denver, CO NIDS data Cheyenne, WY (gif images) Grand Junction, CO Goodland, KS Upper Air Mobile CLASS Denver, CO Grand Junction, CO North Platte, NE Riverton, WY Dodge City, KS Profiler Platteville, CO Granada, CO CSU CHILL, CO Haviland, KS Hillsboro, KS Neodesha, KS McCook, NE Neligh, NE Fairbury, NE Merrinon, NE Medicine Bow, WY Goes 8 Denver (jpeg image) National METAR PIREPS Airmets Colorado Wyoming Nebraska Kansas U.S.A. U.S.A. Convective U.S.A. Sigmets Local Colorado Storm Wyoming Reports Nebraska Kansas Severe Rpts U.S.A. 16 June 1999 - Hourly Collection of Data Time (UTC) 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 97

98

Denver, CO 16 June 1999 1200 UTC Cheyenne, WY 16 June 1999 1851 UTC 99

Thursday, 17 June 1999 Julian Day 168 Meteorological Summary This day was another multicell convection day, but with very low winds aloft. Operations Summary The aircraft were up at about 2220 UTC with storm targets to the west of CHILL. Cloud tops were at about 43 kft with echoes near 60 dbz. Cloud base was at about 10 kft., the freezing level was at about 13.5 kft. A total of 9 runs were made The Sabreliner flew alone at higher altitudes while the T28-Convair flew in formation at lower altitudes. The T28-Convair runs were designated Flight 11 and the Sabreliner runs Flight 12. Flight 11 (T28-Convair) runs. Run 1 was a west to east penetration of an older storm, with the Convair at 21 kft and the T28 at 22 kft. Start and end times of Run 1 were 225600-230300 UTC respectively. Healthy updrafts were encountered, and light to moderate turbulence reported. Run 2 was a reverse course, i.e. roughly east to west, back through the same storm. Start and end times were 230806-232200. Heavy rain and moderate turbulence were encountered. Run 3 was back through the same complex on about a 60 deg heading, with both aircraft then at 21 kft. Start and end time for Run 3 were 2334-2343. Light turbulence and rain were reported. Run 4 was at 19 kft, with start and stop times of 2346-2355 with light-moderate turbulence, rain, and ice encountered. Flight 12 (Sabreliner) runs. The same storm complex sampled by the T28 and Convair along eastwest headings was sampled by the Sabreliner at higher altitudes and at north-south headings. Run 1 was northwest to southeast along the west side of the storm at 28 kft from 2249-2253 UTC. Light-moderate turbulence reported, mixed ice. Run 2 was back up south to north, again along the west side of the storm, from 225720-230930. Light-moderate turbulence, rain, hail, and lightning were reported. Run 3 was back down the west side of the same storm, northwest to southeast at 32 kft, from 231723-232100. Light-moderate turbulence, lightning reported. Run 4 was a return course at about a 340 deg heading on the east side of the storm now, still at 32 kft, from 2323-2330. Cloud tops were now up to about 53 kft in this storm. Light-moderate turbulence was reported. Run 5 was back to the south on the eastern edge. Run 5 was started at 2337, but at 2343, the aircraft escaped from the storm to the east before the second cell in the complex was penetrated, due to a door seal problem and some smoke in the cockpit. No apparent serious damage resulted. All runs were in dual Doppler coverage. Three soundings were launched at 1800, 2100, and 2215 UTC from the CHILL radar site. 100

CHILL reflectivity shown at 13.33 degrees elevation. The scan time is 230009 UTC on June 17, 1999 and corresponds to Run 1 of Flight 11 and Run 2 of Flight 12. The locations of the three aircraft are shown as before. Range rings are every 20 km. 101

Data Type Source Aircraft T-28 Convair Sabreliner Ground CHILL Radars Pawnee NEXRAD NIDS data (gif images) Upper Air Profiler Goes 8 Denver (jpeg image) National METAR PIREPS Airmets Convective Sigmets Local Storm Reports Denver, CO Cheyenne, WY Grand Junction, CO Goodland, KS Mobile CLASS Denver, CO Grand Junction, CO North Platte, NE Riverton, WY Dodge City, KS Platteville, CO Granada, CO CSU CHILL, CO Haviland, KS Hillsboro, KS Neodesha, KS McCook, NE Neligh, NE Fairbury, NE Merrinon, NE Medicine Bow, WY Colorado Wyoming Nebraska Kansas U.S.A. U.S.A. U.S.A. Colorado Wyoming Nebraska Kansas Severe Rpts U.S.A. 17 June 1999 - Hourly Collection of Data Time (UTC) 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 102

103

Denver, CO 17 June 1999 1200 UTC Cheyenne, WY 17 June 1999 1821 UTC 104