On the 14th of August 2005, northwesterly flow was helping to initiate storms over northeastern New Mexico within a region of upslope and moisture convergence. Activity extended southeastward along an instability axis to just west of Amarillo Texas by 2330 UTC. Instability was varied across the region with models indicating an axis of 1000 J/kg of boundary layer CAPE extending northwestward from Big Spring Texas to northeastern New Mexico. The airmass could be typified as a modified continental air mass with trajectories coming increasingly off the Gulf of Mexico. Cloud base temperatures based upon model soundings were expected to be around 13°C to 15°C. The 0000 UTC Amarillo sounding, most representative of the sampled environment indicated CAPE values of 652 J/kg.

Aircraft penetrations were made on the flanks of a severe thunderstorm that developed in Deaf Smith county west of Amarillo. The cloud bases formed along an incline as they developed over a gust front close to the thunderstorm. To the west of the thunderstorm (about 10 miles from the intense aircraft radar echo) the cloud bases were firm at 7100 feet. Further west, the cloud bases were higher by about 1000 feet. Apparently aircraft penetrations were conducted on clouds that were triggered by the gust front to the southwest of the thunderstorm. The clouds had no discernible updraft on the aircraft Vertical Speed Indicator (VSI) at their bases, but they became quite violent higher up. The cloud was pushing erected towers against the apparent strong shear towards the parent storm that was visible in the more mature towers. New growth was apparent on the northwest and the southwest flank of the storm. This thunderstorm produced hail that was larger than 2 inches in diameter.

The cloud droplet concentrations were relatively high throughout the vertical profile with cloud droplet effective diameters varying from around 6 to 19 µm. These cloud droplets were small and did not increase much with height. This indicates that both the warm phase and mixed phase precipitation are very inefficient. The CIP probe data shows that precipitation size droplets were measured mostly above 4.6 km indicating the late initiation of precipitation.

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The remnants of tropical storm Ivan moved onshore on the 23rd of September 2004 and further into southeast Texas on the 24th. Very moist flow off the Gulf and significant moisture convergence over southeast Texas near the center of Ivan resulted in numerous showers and storms over that region. Research aircraft launched from south central Texas to sample convective development over those regions after which it progressed eastward to sample a feeder band coming onshore in the Lake Charles, Louisiana area. Upper level features were rather weak with weak to moderate westerly flow across much of central Texas in advance of a deepening trough over the desert southwest. Deep moisture and strong surface heating resulted in surface based CAPE values of around 1000 j/kg across south central Texas. Scattered convection developed in this region despite the lack of surface focusing mechanisms. By 2200 UTC most of this activity was weakening across south central Texas while feeder bands continued to move onshore in the Beaumont, Texas region. Surface based CAPE based upon the RUC initialization data around Beaumont was near 2000 J/kg at 1900 UTC. Trajectories for the activity over central Texas originated from central Louisiana within moist easterly flow to the north of Ivan. In contrast surface trajectories for Beaumont originated in the central Gulf of Mexico. The 1200 UTC Lake Charles sounding indicated moderate instability with a lifted index of –4 and a positive CAPE value of 633 J/kg. Some substantial low level stability existed as evidenced by a CIN value of 35 J/kg. The aircraft departed the Austin airport at 19:23Z. At 00:07Z the aircraft started conducting aircraft penetrations at 8000 feet over the Lake Charles Airport. Aircraft drop size distribution measurements were taken from 8000 feet above the cloud base level to the cloud tops at 15200 feet.

The cloud droplet concentrations were relatively low with cloud droplet effective diameters ranging from around 24 to 33 µm. This is an immediate indication that the warm phase precipitation was quite active and cloud droplet coalescence was the predominant precipitation forming mechanism. This is because the cloud droplets were large and increased efficiently with height. The CIP shows that precipitation size droplets are measured mostly at 2.6 and 2.8 km indicating the early initiation of precipitation.
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