Convection during the spring and summer months significantly impacts air traffic flow efficiency -- but is notoriously difficult to predict precisely due to its rapid evolution and wide variety of formation mechanisms. This difficulty produces uncertainty in the deterministic forecasts that typically grows with forecast lead time. To capture this uncertainty, the forecast may also need to be represented probabilistically, especially at lead times beyond 1-2 hours. A key challenge is how to translate and convey the forecast in a manner that clearly identifies areas of forecasted aviation impact, and provides a measure of forecast confidence to the user. This talk will present a methodology to create and display a probabilistic weather forecast that could be used by aviation weather forecasters and decision makers.

The Weather Avoidance Field (WAF) is used as a basis for the probabilistic forecasts. The WAF is a derived field that gives the probability that a pilot will avoid a particular stormy area in en route airspace based on observed or forecast precipitation (VIL) and echo tops. A 0-8 hour probabilistic forecast has been developed based on a time-lagged ensemble of WAF forecasts generated from the CoSPA forecast system. A method has been created to generate polygons for low, medium and high probability of expected pilot avoidance in a region, color-coded for low and high confidence forecasts, with an associated value of expected echo tops.

These polygons essentially mimic and could serve as a first guess for the Collaborative Convective Forecast Product (CCFP) produced and issued by forecasters at the Aviation Weather Center (AWC) and the Collaborative Decision Making community. The recommendation is to overlay these first guess polygons on the CoSPA deterministic forecast, to both highlight broad regions of expected impact to air traffic and convey the expected spatial structure of forecasted weather. The first-guess polygons were supplied to AWC for evaluation during their 2011 Aviation Weather Testbed Summer Experiment. This talk will present feedback from aviation experts gathered at the Aviation Weather Testbed on the ability of the CoSPA-based polygons to identify en route convective hazards and potentially serve as a first guess for the CCFP. It will also assess the skill of the polygons at accurately identifying regions of expected aviation impact.

This work was sponsored by the Federal Aviation Administration under Air Force Contract No. FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the United States Government. This research is in response to requirements and funding by the Federal Aviation Administration (FAA). The views expressed are those of the authors and do not necessarily represent the official policy or position of the FAA.