The Mesoscale Predictability Experiment (MPEX): An Ensemble-Forecast-Based Mesoscale Field Campaign

The Mesoscale Predictability Experiment (MPEX) addresses the question of whether experimental, sub-synoptic observations can extend the skill of numerical forecasts of organized (often severe) convection with a lead time of 6-24 h. There are two complementary research foci for MPEX:

• Regional-scale numerical weather prediction (NWP) of convective storms, including analysis and prediction of the upstream, pre-storm mesoscale and sub-synoptic scale environment for regional scale convective forecasting.

• The feedbacks between deep convective storms and their environments, focusing on the upscale effects of deep convective storms on their environment, and how these feed back to the convective-scale dynamics and predictability.

The present talk will focus on observations collected by the NSF/NCAR Gulfstream-5 (GV) aircraft, including a description of the novel method for quantifying forecast sensitivity and preliminary results of reforecasts run using the field data. Given forecasts initialized at 12 UTC on Day 1, sensitivity was defined with respect to forecast metrics centered on 00 UTC of Day 3 (i.e. 36 hours later). These metrics assessed the intensity and coverage of deep convection focused on regions with high ensemble variability. Sensitive regions were defined at 12 UTC on Day 2 based on correlations of 24-h forecast variables with convective attributes at 36 h. Observations were then deployed in those sensitive regions between 09 and 16 UTC of Day 2. These observations included dropsondes and retrievals from a microwave temperature profiler, flown on the GV at roughly 40,000 ft. altitude. During the initiation and maturation of organized convection, ground-based mobile soundings were deployed to (a) quantify the upscale influence of convection and subsequent prediction implications and (b) provide mesoscale validation of forecasts initialized on Day 1. A total of 15 aircraft missions and approximately 20 mobile-sounding missions were conducted. These covered the severe tornadic outbreaks of 20 and 31 May, a low-end derecho on 11 June, and numerous other days featuring severe storms.