1. WARM SEASON CONVECTIVE WIND CLIMATOLOGY FOR THE CCAFS/KSC AREA
Katie Leigh Laro
Plymouth State University, Plymouth, New Hampshire
Background Information
Yearly, Monthly, and Flow Regime Variations
Diurnal Variations
Radar Study Results
Thunderstorms pose a major problem for range operations at the Cape Canaveral Air Force Station (CCAFS) and Kennedy Space Center (KSC). The danger comes not only from lightning, but also from potentially strong winds. The majority of thunderstorms occur during the warm season months of May through September. During this 153-day period, thunder-storms occur on the average of 60 days This study and previous studies were undertaken to develop tools that could be used for training, planning, and operational forecasting of strong winds from thunderstorms in this area. This current research extended and expanded on previous studies (Sanger 1999; Loconto 2006; Cummings et al. 2007; Dinon et al. 2008; and Ander et al. 2009) and analyzed radar and other data over 17 years ( ) to develop a detailed climatology of these convective winds for the Florida Space Coast.
Primary Data Sources:
36 weather towers (many multi-instrumented at various altitudes) on and around CCAFS/KSC that provided peak wind data for every 5- minute interval
High resolution data from WSR-88D radar at National Weather Service/Melbourne, FL
More information:
There is some year to year variation in the number of days with thunderstorm activity over the warm season with 2006 having the fewest days with thunderstorms and 2009 having the most.
Most non-warning level events (<35 knots) were pulse storms, commonly initiated by daytime heating. However, the majority of warning level events (≥35knots) were initiated by a sea breeze front (SBF) and/or outflow boundaries (OFB) from other storms.
Downbursts can occur at any time but are more likely to happen in with late afternoon/early evening. This matches the pattern of thunderstorm frequency, due to greater daytime heating.
While downbursts are less likely to occur early in the morning, when they do, they do not have significantly slower peak wind speeds.
Moderate is the most common cell strength for both warning and non-warning level storms. However, warning-level storms also occur quite frequently with strong cell strength.
July typically has the most days with thunderstorms, but it can sometimes be June or August depending on the year.
Wind Speed Probability
Calculating the probabilities of certain wind speed thresholds for each month has been a very useful tool for planning and forecasting. The table shows that on any given day with thunderstorms in the warm season, there’s a 50.8 percent chance their will be wind speeds at an excess of 30 knots and a 73.1 percent chance of 25 knots or greater.
The most common cell structure for warning level events was linear, whereas for non-warning events, it was cluster. A significant association exists between linear structured cells and high winds, and between cluster shaped cells and weaker winds.
CCAFS/KSC Wind Tower Network
Flow regimes (see chart below) directly relate to the intensity and occurrence of convective events. Lambert (2007) classified the eight flow regimes by the position of the subtropical ridge axis relative to Florida and the resulting low level wind flow. Daily flow regime data were provided for warm-season months. Westerly component regimes are more likely to produce convective storms with stronger winds.
References
Radar Climatology Classifications
Ander, C. A., A. J. Frumkin, J. P. Koermer, and W. P. Roeder, 2009: Study Of Sea-Breeze Interactions Which Can Produce Strong Warm-Season Convective Winds In The Cape Canaveral Area, 16th Conf. on Air Sea Interactions, Jan 2009, Paper J8.3, 14 pp.
Cummings, K. A., E. J. Dupont, A. J. Loconto, J. P. Koermer, and W. P. Roeder 2007: An Updated Warm-Season Convective Wind Climatology for the Florida Space Coast., 16th Conf. on Applied Climatology Jan 07, San Antonio, TX, Paper J3.13.
Dinon, H. A., M. J. Morin, J. P. Koermer, and W. P. Roeder, 2008: Convective winds at the Florida spaceport: year-3 of Plymouth State research, 13th Conf. on Aviation, Range, and Aerospace Meteorology, Jan 2008, New Orleans, LA, Paper 8.5.
Lambert, W. C., 2007: Statistical short-range guidance for peak wind speed forecasts on Kennedy Space Center/Cape Canaveral Air Force Station: Phase-I results. NASA Contractor Report CR pp.
Loconto, A. N., 2006: Improvements of warm-season convective wind forecasts at the Kennedy Space Center and Cape Canaveral Air Force Station. M.S. Thesis, Dept. of Chemical, Earth, Atmospheric and Physical Sciences, Plymouth State University, Plymouth, NH, 92pp.
Sanger, N. T., 1999: A Four-Year Summertime Microburst Climatology And Relationship Between Microbursts And Cloud-To Ground Lightning Flash Rate For The NASA Kennedy Space Center, Florida: , M.S. Thesis, Texas A&M University, Aug 99, 116pp.
Cell Initiation
Cell Structure
Cell Strength
SBF and OFB
Linear
Weak/Broken
SBF only
Individual Cell
Moderate
OFB only
Cluster
Strong
No SBF or OFB
Dinon et al. (2008) created a method of classifying the radar characteristics of each convective period into six categories. This table shows three of the six categories. The other three are group movement, individual cell movement, and the location of the strongest wind relative to the generating cell.
Boundary Types: SBF = Sea Breeze Front,
OFB = Outflow Boundary
Cell Structure: Self Explanatory
Cell Strength: Maximum Reflectivity < 45 dBZ → Cell Strength = Weak,
Maximum Reflectivity dBZ → Cell strength = Moderate,
Maximum Reflectivity > 55 dBZ → Cell Strength = Strong
Acknowledgments
The NASA New Hampshire Space Grant Consortium provided the majority of funding for this study, along with the continuing support and expertise of the 45th Weather Squadron, especially Mr. William Roeder, and personnel from the NASA Applied Meteorology Unit.
KSC/CCAFS weather tower network used to collect wind data for the study. The 9 towers in white were excluded from the study due to poor data availability.