Simulating Extreme Precipitation over the Arabian Peninsula Using a Convective-Permitting Subseasonal Reforecast Product

Though the Arabian Peninsula is one of the driest places in the world, it occasionally experiences extreme precipitation events associated with organized convection. For example, on 25 November 2009, rainfall exceeding 70 mm triggered a flash flood event in Jeddah, Saudi Arabia, claiming hundreds of lives and substantially damaging infrastructure. Similar extreme precipitation events have occurred in subsequent years. In order to assess potential predictability of extreme precipitation in the Arabian Peninsula, we perform retrospective forecast simulations of several extreme events occurring over the period 2000 to 2018, out to a sub-seasonal timescale (3-4 weeks). Using the Advanced Research version of Weather Research and Forecasting Model (WRF-ARW) at convective-permitting resolution (2 km), we dynamically downscale Climate Forecast System model Version 2 (CFSv2) sub-seasonal reforecasts, available from the North American Multimodel Ensemble (NMME). The simulation is initiated for various forecast lead times using five ensemble members, each of which is initialized on different days. Model simulated precipitation is evaluated against various precipitation products, including Global Precipitation Measurement (GPM) system, Climate Prediction Center morphing technique (CMORPH), and locally available in-situ rain gauge measurements. The convective-permitting WRF simulations substantially improve the representation of precipitation relative to the CFSv2 reforecast, with respect to spatial distribution and timing. A specific focus in the presentation of the results will be the potential value added by use of convective-permitting modeling to forecasting extreme events at sub-seasonal timescale