National Severe Storms Laboratory

Understanding the Characteristics of Convection in Convection Allowing Models

Humphrey Lean

UK Met Office

09 May 2016, 4:00 PM

National Weather Center, Room 1350
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Convection Allowing Models (CAMS) have provided a step change improvement in the representation of convection compared to the previous generation of order 10km models. In the UK, for example, the Met Office has been running the UKV, a 1.5km version of the Unified Model (UM), since 2009 and this is now a workhorse of UK forecasting. Despite this success there are a number of issues with the representation of convection. Examples include biases in the distribution of rain rates, morphology of convective cells and timing of convection. I will describe, with examples, these biases as we see them in the UM. Research work to understand and address these issues will be described. This includes detailed comparisons of the models with observations, comparisons of the performance of the models with different physics and with different model gridlengths, particularly going to higher resolutions. We are also working to understand the performance of the model in different parts of the world and different meteorological situations. An important aspect of this is to understand which of the above biases are specific to the UM and which are generally true across CAMS based on other models also. We can shed some light on this question by making statistical comparisons of radar data from the 2015 Hazardous Weather Testbed SFE with the runs of the UM and WRF. I will show these comparisons and draw some preliminary conclusions.