CASA data improves accuracy of NWS forecaster wind assessments and forecaster confidence

When National Weather Service forecasters expect wind speeds to exceed 50 kts (58 mph), they issue a severe thunderstorm warning to alert the public. In fall 2008, 16 active NWS forecasters reviewed 6 different archived weather cases to measure the impact of CASA's high resolution, lower troposphere data on their wind predictions.  They reviewed cases with NEXRAD radar data only (the current technology) and cases with both CASA and NEXRAD data.  Their predictions were compared to measurements from ground-based sensors. The results show that forecasters using CASA and NEXRAD data made wind assessments that were 30% more accurate (as measured by mean absolute error) than assessments made with NEXRAD data only, a statistically significant difference. Using a seven-point scale, forecasters also self-reported being significantly more confident when CASA data were available.  It is likely that these more accurate and confident wind assessments will lead to improved severe thunderstorm warnings. With the addition of CASA data, forecasters said they would issue warnings more often for the cases where actual wind speeds were close to or above the severe threshold.  Equally important, forecasters chose not to issue warnings for cases where actual wind speeds were under severe limits. This impact on warnings will be verified in subsequent studies.

NWS Forecasters completing the Wind Assessment Experiment at the National Weather Association meeting