Weeks 3-4/S2S Webinar Series: Hybrid Prediction of Weekly Tornado.../Predictability of the UFS...

Dr. Zhuo Wang, University of Illinois - "Hybrid Prediction of Weekly Tornado Activity out to Week 3: Utilizing Weather Regimes"

Tornadoes are one of the high-impact weather phenomena that can induce life loss and property damage. Here, we investigate the relationship between large-scale weather regimes and tornado occurrence in boreal spring. Results show that weather regimes strongly modulate the probability of tornado occurrence in the United States due to changes in shear and convective available potential energy, and that persisting weather regimes (lasting 3 days) contribute to greater than 70% of outbreak days (days with 10 tornadoes) . A hybrid model based on the weather regime frequency predicted by a numerical model is developed to predict above/below normal weekly tornado activity and has skill better than climatology out to week 3. The hybrid model can be applied to real-time forecasting and aide in mitigation of severe weather events.

Dr. V. Krishnamurthy, George Mason University - "Predictability of the UFS over CONUS at Subseasonal Time Scale during Boreal Summer"

The predictability of the Unified Forecast System (UFS) Coupled Model Prototype 2, developed by the National Centers for Environmental Prediction, is assessed over the continental United States (CONUS) for the boreal summer. The retrospective forecasts of low-level horizontal wind, precipitation and 2m temperature for 2011–2017 are examined to determine the predictability at subseasonal time scale. Using a data-adaptive method, the leading modes of variability are obtained and identified to be related to El Niño-Southern Oscillation (ENSO), intraseasonal oscillation (ISO) and warming trend. The sources of better predictability are identified by examining the forecast errors and correlations in the weekly averages of the leading modes of variability. During the boreal summer, the ISO followed by the trend in UFS are found to provide better predictability in weeks 1–4 compared to the ENSO mode and the total anomaly. The western part of the CONUS seems to have better predictability on weekly time scale in all the three modes.