The 2014 Upgrade to the Lightning Warning Areas Used By 45th Weather Squadron

The 45th Weather Squadron (45 WS) implemented new lightning warning areas in May 2014.  The previous areas had too much overlap both geographically and temporally.  Some areas were less than 1 nmi apart, which is at or beyond the state of the art in lightning forecasting for lightning watches, but feasible for warnings based on detected lightning.  In addition, some adjacent lightning warnings were issued simultaneously 98% of the time, suggesting that the two areas were essentially one area and could be combined.  The 45 WS streamlined their lightning warning areas to overcome these shortfalls, optimize the areas protecting multiple facilities, improve safety, and to allow the forecasters more time to think about the weather rather than managing the lightning warning process.

The new 45WS lightning warning process consists of 10 warning circles with a radius of 5 or 6 nmi depending if one or several facilities are being covered, respectively.  The previous process used 13 circles, each of 5 nmi radius, designed to protect individual facilities.  The new lightning warning circles are designed to provide at least 4.5 nmi distance to the nearest lightning before a warning is issued.  This is consistent with safety standards requiring 5 nmi standoff as used at large facilities such as Air Force runways.  In addition, the 4.5 nmi safety buffer provides an excellent compromise between safety and operational impact given studies of local lightning strike distances.  In addition, the 45 WS warns on lightning aloft, which typically provides a few minutes of additional lead-time as compared to warning on cloud-to-ground lightning, as is common practice at other locations.  The 45 WS also warns on the edge of the detected lightning field, which typically provides a mile or more of additional stand-off distance as compared to warning on the distance from the center of the thunderstorm as is common practice.

One of the biggest changes of the new lightning warning circles was optimizing the ones protecting multiple facilities.  Facilities requiring lightning warnings that were within about 1 nmi of each other are now covered by a single warning circle with a radius of 6 nmi.  This would increase the time each facility spends under lightning warnings.  However, the 45 WS felt the streamlined process would improve warning quality by allowing the forecasters more time to analyze the weather and perhaps end the warnings quicker, rather than manage the more complicated process.  In addition, the local lightning flash density climatology was considered to reduce the increase in warning time.  Some single facilities that covered large areas and were also assigned 6 nmi warning circles to ensure the entire facility received the desired 4.5 nmi safety buffer to the closest lightning without a warning being issued.  While this would increase the amount of time the facility would be under lightning warnings, this was obviously was justified to improve safety.

The labels of the lightning warning circles were changed to improve clarity in communicating warning status.

Finally, 45 WS discovered that the previous lightning warning circles were displayed to a precision of only 0.01 degree in latitude/longitude due to software limitations when implemented.  This led to display location errors of over 0.5 nmi.  The current display software allowed precision of 0.00001 degrees and the new lightning warning circles were displayed with this much greater accuracy.

The new lightning warnings were implemented in May 2014 after an extensive coordination and education process to ensure the users of the lightning warnings were ready for the new process.  May was chosen to allow about a month of use for familiarization before the start of the lightning season.