NEW NOAA WEB SITE PROVIDES FAA WITH MONTH-BY-MONTH
ANALYSIS OF THUNDERSTORMS

June 30, 2005 — “Supporting the nation’s commerce with information for
safe, efficient, and environmentally sound transportation is one of NOAA's primary goals. Helping the U.S. Federal Aviation Administration and the airlines reduce air traffic delays is a vital NOAA effort toward achieving this goal,” says Jack May, director of the NOAA National Weather Service's Aviation Weather Center in Kansas City, Mo. NOAA's new aviation weather Web site enables the FAA, airlines and others to monitor and analyze thunderstorm activity across the United States in their effort to improve the flow of traffic through the nation’s airways.

The strong winds, heavy precipitation, hail, severe turbulence and icing that accompany thunderstorms prevent safe takeoffs and landings and cause planes to veer from planned routes. In trying to understand the ingredients of factors that cause air traffic delays, the FAA did not have a good way to quantify significant thunderstorm activity over the country. Thanks to two NOAA organizations, now they do. (Click on NOAA image to the right for a larger view of the image showing thunderstorms and the resulting air traffic flow patterns in and around New York City. Please credit "NOAA/Flight Explorer.").

MONTHLY THUNDERSTORM ANALYSIS PRODUCT
What started out as a research project by the NOAA Aviation Weather Center forecaster Jonathan Slemmer has become a Federal Aviation Administration tool used to routinely assess the impact of thunderstorms on the nation's air traffic.

It all started with Slemmer's curiosity about how aviation thunderstorm advisories (known as Convective SIGMETs or SIGnificant MEteorological Information) were geographically distributed throughout the year. Slemmer obtained archived advisories from the NOAA National Climatic Data Center in Asheville, N.C., and generated summary maps and graphs for each month. He shared the analyses with the FAA, who were intrigued — stating that the monthly geographic distribution of thunderstorms supplied an important factor in evaluating air traffic efficiency.

In a letter to Slemmer, FAA Air Traffic Organization CEO Russell Chew said, “We are using the information that you supplied to great advantage in our analysis of traffic delays” and asked for this information monthly.

After several months of collaboration with the FAA, Jesse Enloe, a climatologist with the National Climatic Data Center (working with the AWC, part of the NOAA National Weather Service) has developed a Web site, which allows the FAA, airlines, pilots and general public to view the monthly distribution of Convective SIGMETs and the departures from the average. Graphical analyses are available for each month dating back to 1995. Displays are available across the continental United States, by region, by air route traffic control region and by major airport vicinity.

Convective SIGMETs are used in the analyses rather than weather radar data for several reasons:

• The volume of Convective SIGMETs data is a small fraction of corresponding radar data.
• AWC forecasters consider lightning detection in addition to radar echo strength in determining if Convective SIGMET criteria is reached.
• Convective SIGMETs are issued for thunderstorms with criteria significant to aviation.

Monthly Distribution Of Aviation Thunderstorm Advisories
Maps generated from this Web site depict the monthly geographic distribution of aviation thunderstorm advisories (or Convective SIGMETs) to aid the FAA and others in evaluating the impact of thunderstorms on U.S. airspace. Convective SIGMETs are issued by the NOAA AWC as a means of advising aircraft pilots of convective activity that is deemed hazardous to aviation. Convective SIGMETs are text bulletins routinely issued on an hourly basis at 55 minutes past the hour, as well as times between hours (non-routine issuances) when areas of convection develop rapidly. Each Convective SIGMET is a subjectively drawn polygon, line or circle that depicts convection whenever a specified set of criteria is met. (Click on NOAA image to the right for a larger view of the map and graph depicting the average frequency of thunderstorms in the United States during the month of June 2004. Please credit "NOAA.")

The maps on the new Web site are generated from Convective SIGMET text bulletins, which are collected and archived on a daily basis at NCDC. At the end of each month, all Convective SIGMET reports are compiled and subjected to an analysis routine that identifies the location of all Convective SIGMETs that were issued during the month. (Non-routine Convective SIGMET reports are not included in this analysis in an effort to avoid double-counting the occurrence of Convective SIGMET reports.) The location of each convective object (cell, area or line) is based on latitude/longitude coordinates, which are made to overlay an array of eight km by eight km grid boxes across the continental United States and its surrounding waters. As each Convective SIGMET is evaluated, the eight km by eight km grid boxes that are part of the Convective SIGMET object are identified and tallied throughout the month. The Convective SIGMET frequency (depicted on the map using color coding) is the total number of "hits" per grid box divided by the total number of hours during the month.

The frequency of Convective SIGMET reports was calculated from January 1995 through December 2004 and the average frequency of occurrence throughout the contiguous United States determined for each month. Calculation of the 10-year averages for each month allowed for the subsequent calculation of Convective SIGMET departures from average for any month within the 10-year period, as well as any month subsequent to that period. As such, updates to the Convective SIGMET database continue to be made and maps of total Convective SIGMET, frequency as well as Convective SIGMET departures from average (anomaly), are provided each month. (Click on NOAA image to the right for a larger view of the map and graph depicting the 10-year departures from average for thunderstorms in the United States during the month of June 2004.Please credit "NOAA.")

Results
"Convective SIGMET maps for the period between January 1995 through December 2004 suggest the occurrence of an increase in the frequency of convective activity during this 10-year period," said Jay Lawrimore, chief of the NOAA Climate Monitoring Branch at the NCDC. However, it is unclear whether this increase is due to shifting weather patterns or results from improvements in technology and forecasting procedures that result in an increasing number of Convective SIGMET reports in the first decade of the 21st century.

Maps for any month from January 1995 to the present can be generated using pull down menus. Currently, maps for the contiguous United States, four regions (Northeast, South, Central and Southwest), the 20 air traffic control centers and 20 of the nation's major airports are available. Each airport is presented with 75 nautical mile circles surrounding the airport, with the exception of Washington Dulles, which has a 100 nautical mile circle and LaGuardia, which has a 90 nautical mile circle. The Convective SIGMET summary graphics can be seen on NOAA's new aviation weather Web site.

Additional aviation weather products and information are available on the NOAA Aviation Weather Center Web site.

Relevant Web Sites

NOAA Aviation Weather Center

A Pilot's Guide to Aviation Weather Services

NOAA Aviation Theme Page

NOAA Aviation Digital Data Service

NEW AVIATION WEATHER PRODUCT AIDS ICING CONDITION FORECASTS

INTERNET-BASED PILOT REPORTS ALLOW NOAA TO IMPROVE AVIATION FORECASTS AND SAFETY

NOAA's AVIATION WEATHER SERVICES

Media Contact:
Greg Romano, NOAA Weather Service, (301) 713-0622 ext. 164 or Chris Vaccaro, NOAA Weather Service, (301)713-0622 x134