Ryan Torn

Ryan Torn

Studies weather forecasting models, tropical cyclones, and atmospheric predictability

The World Within Reach
Ryan Torn
Associate Professor

College of Arts and Sciences
Department: Atmospheric and Environmental Sciences


ES 229




Understanding the sources and evolution of errors in numerical weather prediction (NWP) models is critical to improving forecasts of various atmospheric phenomenon. Errors can originate from two primary sources: the model initial conditions (i.e., the analysis), or errors in the model formulation (i.e., model error). Initial conditions for NWP models are generated via data assimilation, whereby new observation information is incorporated into a model's short-term forecast to produce a best estimate of the atmospheric state. Improvements to the initial conditions can be achieved by either adjusting how observations impact the model state, or taking observations in regions where forecast errors quickly grow.

My research focuses on trying to understand atmospheric predictability by determining the source and growth of errors within numerical models across a number of timescales using ensemble forecasts. Having knowledge about error growth processes within numerical models also provides insight into the governing dynamics. At the present time, I am working on understanding the predictability of tropical cyclone intensity and structure, African Easterly Waves, organized convection and extratropical transition. This work involves collaborations with the National Center for Atmospheric Research, University of Washington, University of Miami and the NOAA Hurricane Research Division.


2002, B.S., University of Wisconsin-Madison.
2007, Ph.D., Atmospheric Science, University of Washington.

Research Interests

Predictability, data assimilation, synoptic and mesoscale meteorology.

Additional Information

Ryan's Curriculum Vitae

Torn Research Group


Berman, J. D., R. D. Torn, G. S. Romine, and M. L. Weisman, 2017: Sensitivity of Northern Great Plains Convection Forecasts to Upstream and Downstream Forecast Errors. Mon. Wea. Rev., 145, 2141-2163 PDF File.

Papin, P. P., L. F. Bosart, R. D. Torn, 2017: A Climatology of Central American Gyres. Mon. Wea. Rev., 145, 1983–2000 PDF File.

Torn, R. D., G. S. Romine, T. J. Galarneau Jr., 2017: Sensitivity of Dryline Convection Forecasts to Upstream Forecast Errors for Two Weakly Forced MPEX Cases. Mon. Wea. Rev., 145, 1831-1852 PDF File.

Rios-Berrios, R., R. D. Torn, 2017: Climatological analysis of tropical cyclone intensity changes under moderate vertical wind shear. Mon. Wea. Rev., 145, 1717-1738 PDF File.

Romine, G. S., C. S. Schwartz, R. D. Torn, M. L. Weisman, 2016: Impact of assimilating dropsonde observations from MPEX on ensemble forecasts of severe weather events. Mon. Wea. Rev., 144, 3799-3823 PDF File.

Torn, R. D., 2016: Evaluation of atmosphere and ocean initial condition uncertainty and stochastic exchange coefficients on ensemble tropical cyclone intensity forecasts. Mon. Wea. Rev., 144, 3487-3506 PDF File.

Lamberson, W., R. D. Torn, L. F. Bosart, L. Magnusson, 2016: Diagnosis of the source and evolution of medium-range forecast errors for extratropical cyclone Joachim. Wea. Forecasting, 31, 1197-1214 PDF File.

Rios-Berrios, R., R. D. Torn, C. Davis, 2016: An ensemble approach to investigate tropical cyclone intensification in sheared environments. Part II: Ophelia (2011). J. Atmos. Sci., 73, 1555-1575 PDF File.

Rios-Berrios, R., R. D. Torn, C. Davis, 2016: An ensemble approach to investigate tropical cyclone intensification in sheared environments. Part I: Katia (2011). J. Atmos. Sci. 73, 71-93 PDF File.

Weisman, M. L., R. J. Trapp, G. S. Romine, C. Davis, R. Torn, M. Baldwin, L. Bosart, J. Brown, M. Coniglio, D. Dowell, A. C. Evans, T. J. Galarneau Jr., J. Haggerty, T. Hock, K. Manning, P. Roebber, P. Romashkin, R. Schumacher, C. S. Schwartz, R. Sobash, D. Stensrud, S. Trier, 2015: The Mesoscale Predictability Experiment (MPEX). Bull. Amer. Meteor. Soc. 96, 2127-2149 PDF File.

Torn, R. D., and G. Romine, 2015: Sensitivity of Central Oklahoma convection forecasts to upstream potential vorticity anomalies during two strongly-forced cases during MPEX. Mon. Wea. Rev. 143 4064-4087 PDF File.

Chen, S.-H., Y.-C. Liu, T. R. Nathan, C. Davis, R. Torn, N. Sowa, C.-T. Cheng, J.-P. Chen, 2015: Modeling the effects of dust-radiative forcing on the movement of Hurricane Helene (2006). Quart. J. Roy. Meteor. Soc. 141, doi:10.1002/qj.2542 PDF File.

Torn, R. D., and G. J. Hakim, 2015: Comparison of wave packets associated with extratropical transition and winter cyclones. Mon. Wea. Rev. 143, 1782-1803 PDF File.

Torn, R. D., Whitaker, J. S. Pegion, P., Hamill, T. M., Hakim, G. J., 2015: Diagnosis of the source of GFS medium range track errors in Hurricane Sandy (2012). Mon. Wea. Rev., 143, 132-152. PDF File.

Majumdar, S. J., and R. D. Torn, 2014: Probabilistic verification of global and mesoscale ensemble forecasts of tropical cyclogenesis. Wea. Forecasting, 29, 1181-1198. PDF File.

Torn, R. D., 2014: The impact of targeted dropwindsonde observations on tropical cyclone intensity forecasts of four weak systems during PREDICT. Mon. Wea. Rev., 142, 2860-2878. PDF File.

Cavallo, S. M., R. D. Torn, C. Snyder, C. Davis, W. Wang and J. Done, 2013: Evaluation of the Advanced Hurricane WRF data assimilation system for the 2009 Atlantic hurricane season. Mon. Wea. Rev., 141, 523-541. PDF File.

Torn R. D. and D. Cook, 2013: The role of vortex and environment errors in Hurricanes Danielle and Karl (2010) genesis forecasts. Mon. Wea. Rev., 141, 232-251. PDF File.

Torn, R. D. and Davis, C. A., 2012: The influence of shallow convection on tropical cyclone track forecasts. Mon. Wea. Rev., 140, 2188-2197. PDF File.

Torn, R. D. and C. Snyder, 2012: Uncertainty of tropical cyclone best track information. Wea. Forecasting, 27, 715-729. PDF File.

Montgomery, M. T., C. Davis, T. Dunkerton, Z. Wang, C. Velden, R. Torn, S. Majumdar, F. Zhang, R. K. Smith, L. Bosart, M. M. Bell, J. S. Haase, A. Heymsfield, J. Jensen, T. Campos and M. A. Boothe, 2011: The Pre-Depression Investigation of Cloud Systems in the Tropics (PREDICT) Experiment: Scientific Basis, New Analysis Tools, and Some First Results. Bull. Amer. Meteor. Soc., 93, 153-172. PDF File.

Davis, C., W. Wang, S. Cavallo, J. Done, J. Dudhia, S. Fredrick, J. Michalakes, G. Caldwell, T. Engel, and R. Torn, 2011: High-resolution hurricane forecasts. Computing in Science and Engineering, 13 (1), 22–30 PDF File.

Torn, R. D., 2010: Performance of a Mesoscale Ensemble Kalman Filter (EnKF) During the NOAA High-Resolution Hurricane Test. Mon. Wea. Rev., 138, 4375–4392. PDF File.

Davis, C., W. Wang, J. Dudhia, and R. Torn, 2010: Does increased horizontal resolution improve hurricane wind forecasts. Wea. Forecasting, 25, 1826–1841. PDF File.

Torn, R. D., 2010b: Diagnosis of the Downstream Ridging Associated with Extratropical Transition Using Short-term Ensemble Forecasts. J. Atmos. Sci., 67, 817–833. PDF File.

Torn, R. D., 2010a: Ensemble-based sensitivity analysis applied to African Easterly Waves. Wea. Forecasting, 25, 61–78. PDF File.

Torn, R. D., and G. J. Hakim, 2009: Initial condition sensitivity of Western-Pacific extratropical transitions determined using ensemble-based sensitivity analysis. Mon. Wea. Rev., 137, 3388-3406. PDF File.

Anderson, J, and T. Hoar, K. Raeder, H. Liu, N. Collins, R. Torn, and A. Arellano, 2008: The Data Assimilation Research Testbed: A community data assimilation facility. Bull. Amer. Meteor. Soc., 90, 1283-1296 PDF File.

Torn, R. D., and G. J. Hakim, 2009: Ensemble Data Assimilation applied to RAINEX observations of Hurricane Katrina (2005). Mon. Wea. Rev., 137, 2817-2829. PDF File

Hakim, G. J., and R. D. Torn, 2008: Ensemble Synoptic Analysis. Fred Sanders Monograph, Lance Bosart and Howard Bluestein, eds., American Meteorological Society, 147--161. Please contact me for a copy.

Torn, R. D., and G. J. Hakim, 2008: Performance characteristics of a pseudo-operational Ensemble Kalman Filter. Mon. Wea. Rev., 136, 3947--3963. PDF File.

Torn, R. D., and G. J. Hakim, 2008: Ensemble-based sensitivity analysis. Mon. Wea. Rev., 136, 663--677. PDF File.

Dirren, S., R. D. Torn, and G. J. Hakim, 2007: A data assimilation case-study using a limited-area ensemble Kalman filter. Mon. Wea. Rev., 135, 1455--1473. PDF File.

Torn, R. D., G. J. Hakim, and C. Snyder, 2006: Boundary conditions for a limited-area ensemble Kalman filter. Mon. Wea. Rev., 134, 2490--2502. PDF File.