A review of the VAS assessment during the 1985 PROFS summer exercise
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A review of the VAS assessment during the 1985 PROFS summer exercise

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A review of the VAS assessment during the 1985 PROFS summer exercise


  • Description:
    An operational Visible and Infrared Spin-Scan Radiometer Atmospheric Sounder (VAS) assessment was conducted as part of the Program for Regional and Observing Forecasting Services (PROFS) 1985 summer forecasting exercise from 15 May through 23 August. The exercise focused on nowcasting severe weather, specifically the issuance of watches and warnings for a 150 km area surrounding Boulder, Colorado. The PROFS workstation produces three VAS image products on a scheduled basis for three spatial scales: local, regional, and national. The products depict precipitable water (low-level water vapor), upper-level water vapor, and convective stability. In addition to the image products, graphic products are created on user demand from VAS sounding data received in near real time from the Advanced Satellite Products Project. The VAS assessment team reviewed the previous day's weather with a focus on VAS product utility towards the convective forecast problem. Findings were documented daily in a log book. In addition, the assessment team attended daily weather discussions led by the exercise forecasters consisting of staff from the Environmental Research Laboratories and other agencies, including the private sector. The interaction with participating forecasters provided information on daily VAS product utilization and led to several improvements in the products. Assessment results showed the 6.7 micrometer upper-level water vapor imagery to be the most informative VAS image product. The quality of the low-level water vapor product was directly dependent on the amount of available precipitable water in the atmosphere. Cloud contamination adversely affected the quality of the low-level water vapor and stability products especially during severe weather events. National and regional scale products received much more attention than the local scale products. Bulk parameters derived from VAS soundings showed more utility than the sounding data themselves. Cloud contamination and frequent periods without VAS data caused many real-time forecasters to view VAS products as unreliable. Lack of VAS data prevented a complete assessment of VAS nowcast potential; however, indications are that VAS is more useful for short-range forecasts (3 to 6 hours) than for nowcasts (0 to 90 minutes).
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