Forecast Improvements
NSSL Project 1 – Convective Weather Research: Predicting the Longevity of Mesoscale Convective Systems
Funding Type: CIMMS Task II
Objectives
Examine a large data set of observed proximity soundings to identify predictors
of MCS dissipation and to improve our understanding of MCS environments;
the ultimate goal of this work is to develop forecast tools that provide
probabilistic guidance on the maintenance of MCSs with a focus on the
3-12 hour time scale, which could benefit Day 1 Severe Weather Outlooks,
Mesoscale Discussions, and the issuance of Severe Weather Watches at
SPC and short-term forecasts issued by local NWS forecast offices.
Accomplishments
Several environmental factors that can be used to predict the dissipation
of MCSs were identified in this study. Shear vector magnitudes over very
deep layers are the best discriminators among hundreds of kinematic and
thermodynamic variables. The lapse rates over a significant portion of
the convective cloud layer, the convective available potential energy,
and the deep-layer mean wind speed are also very good discriminators
and collectively provide a high level of discrimination between the mature
and dissipation soundings as revealed by linear discriminant analysis.
Probabilistic equations developed from these variables used with short-term
numerical model output show utility in forecasting the transition of
an MCS with a solid line of convection to a more disorganized system
with unsteady changes in structure and propagation. This method to forecast
the longevity of MCSs has been transferred to operations at the SPC and
the NWS Forecast Office at LaCrosse, WI.
This work has been completed.
Publications
Coniglio, M.C., H.E. Brooks, S.F. Corfidi, and S.J. Weiss, 2007: Forecasting
the maintenance of quasi-linear mesoscale convective systems. Wea. Forecasting,
22, 556-570.
Coniglio, M.C., M. Bardon, K. Virts, and S.J. Weiss, 2006: Forecasting the maintenance of mesoscale convective systems. 23rd Conf. on Severe Local Storms, Amer. Meteor. Soc., St. Louis, MO, CD-ROM P2.3.
An example of a 9 h forecast of the MCS maintenance probability (MMP) calculated from Rapid Update Cycle (RUC) output valid at 1800 UTC on 20 June 2005. Values of MMP increase in 10% increments, from 10% in light blue to 90% in dark red. The thick green lines indicate the hourly position of the leading edge of a quasi-linear MCS that occurred in the morning and afternoon of 20 June 2005 (times, in UTC, are indicated in yellow) in the upper Midwest. The system propagated steadily forward and remained strong as it moved through the region of MMP values of 70 - 90% but became more disorganized and gained back building characteristics as it moved through the gradient to low MMP values.