Professional Pilot, October 2017

The Southeast Although the boundaries of what we term the SE US vary by whom one asks the region of the continental US from the Carolinas and Florida on the east stretching to Mississippi in the west and north to Tennessee is normally considered the SE US Less frequently the region may be extended to include Louisiana Arkansas Kentucky Virginia and even on occasion West Virginia Maryland and Delaware This region is home to nearly 90 million people and has around 360 public airports with hundreds more private airstrips and air parks Many of these airports such as MIA Miami FL CLT Charlotte NC and MSY New Orleans LA are major commercial hubs with ATL Atlanta GA being the busiest airport in the world As such the region sees thousands of business commercial and GA operations every day and is crisscrossed by dozens of major flight corridors Given such dense air traffic it is easy to see how even the slightest trace of adverse weather can produce significant disruptions and the SE has a wide variety of weather makers from which it can choose The reason for the varied weather that pilots may encounter in this region is due to its geography For starters the SE rests largely in the subtropics but extends into the southern middle latitudes This means that it is often a mixing ground for cooler and drier air masses from the north and 46 PROFESSIONAL PILOT October 2017 warmer and humid air masses from the south Then there is the large coastline as this region is bordered by warm ocean water to both the south and east Warm air and warm water ensure a largely endless supply of latent energy in the form of water vapor evaporated into the atmosphere Additionally the coastal transition between land and water sets up a local circulation called the sea breeze The greater capability of the water to absorb and store energy means that solar radiation heats up the land more quickly than the water In turn this heats the air over the land making it more buoyant When it rises cooler but humid air is drawn in from over the adjacent water often providing the fuel to transform dry convection into mid day air mass thunderstorms The boundary of the inland flow is called the sea breeze front and can push dozens of miles inland As the sun sets the circulation reverses as the land cools faster than the water and the storms track back offshore only to return the next day Pilots operating out of some coastal airports can almost set their clocks by the passage of the sea breeze front Coastal storms Because it is a peninsula Florida is also the most active part of the SE for thunderstorms In fact with an average of over 100 thunderstorm days per year central Florida has more thunderstorms annually than any other Average number of thunderstorm days per year Average number of days with thunderstorms across the US The geography of the Southeast US and in particular Florida helps the region lead the nation in the frequency of storms though most do not become severe place in the US One reason is that the sea breeze front often operates on both the Atlantic and Gulf coasts and as the 2 fronts converge they enhance the uplift of the warm and humid air caught in between On days where this occurs the section of the peninsula between GNV Gainesville FL and FLL Ft Lauderdale FL may see several dozen individual afternoon storm cells The coast also has a similar influence stretching around the Florida panhandle to MOB Mobile AL and MSY which sees a similarly high number of thunderstorm days per year Most of these coastally influenced storms are air mass storms That is they are formed simply due to local instability resulting in hot and humid air rising from the surface into an environment with little or no upper level windshear like one might expect in the vicinity of the jet stream These are often called ordinary thunderstorms as opposed to severe or supercells and because of the lack of tilting of the convection column by windshear when the downdraft materializes it tends to collapse back on the updraft killing the cell within perhaps a half hour This is not to say that air mass storms dont present a danger to aircraft The atmosphere of the subtropics is very warm and the troposphere extends to at least 30000 ft in winter and as much as 60000 ft in summer Depending on the stability of the upper levels of the troposphere storms in this warm and humid envi Key More than 80 days 65 to 80 days 50 to 65 days 40 to 50 days 30 to 40 days 20 to 30 days 10 to 20 days 0 to 10 days