thunderstorms off the Florida Coast are caused by the warm  water of the Gulf Stream heating the surface air, while the  upper air is cooling by radiation to space. This heating from  below produces thermal convection over the water. When  the sun rises, the heat balance necessary to maintain storm  formation over the water is destroyed. By day, the storms  appear to move inward over the land areas, but actually  dissipate off the coast and re-form over the hot landmass.  The heated land surface sets up an unstable lapse rate over  the Peninsula and causes storm development to continue until  nocturnal cooling occurs. Usually, convective type storms  are randomly distributed and easily recognized.  lost its moisture and energy in the prefrontal thunderstorms.  In the United States, tornadoes are frequently associated  with strong prefrontal squall lines. Pre-frontal squall line  thunderstorms are indicated on a surface weather map by an  alternate dash-dot-dash line (display). The distribution of stationary front thunderstorms is  controlled by the slope of the frontal surface. Steeply sloped  stationary fronts tend to have lines of storms, whereas shallow  stationary fronts tend to have widely scattered storms. Occluded front thunderstorms are associated with the  two types of occluded fronts (warm front and cold front  occlusions), and are usually cold front thunderstorms that  have been moved into the area of warm frontal weather by  the occlusion process. They are found along the upper front,  and are normally strongest for a distance of 50 to 100 miles  north of the peak of the warm sector.  Orographic thunderstorms will form on the windward side  of a mountain if conditionally unstable air is lifted above the  level of free convection. The storm activity is usually scattered  along the individual peaks of the mountains. Occasionally,  however, this activity may form a long unbroken line of  storms similar to a squall line. The storms persist as long as  the circulation causes upslope motion. From the windward  side of the mountains, identification of orographic storms  may sometimes be difficult because the storm clouds are  obscured by other clouds (usually stratiform). Almost without  exception, orographic thunderstorms enshroud mountain  peaks or hills.  The two types of air mass thunderstorms are locally convective  and orographic. Both types form within air masses, and are  randomly distributed throughout the air mass.  Convective thunderstorms are often caused by solar heating  of the land, which provides heat to the air, thereby resulting in  thermal convection. Relatively cool air flowing over a warmer  water surface may also produce sufficient convection to cause  thunderstorms. The land-type convective thunderstorms  normally form during the afternoon hours, after the Earth  has gained maximum heating from the sun. If cool, moist,  conditionally unstable air is passing over this land area,  heating from below will cause convective currents, thereby  resulting in towering cumulus or thunderstorm activity.  Dissipation usually occurs during the early evening hours, as  the land begins to lose its heat to the atmosphere. Although  convective thunderstorms form as individual cells, they may  become so numerous over a particular geographical area that  continued flight cannot be maintained.  The minimum factors essential to the formation of a  thunderstorm are conditionally unstable air with relatively  high moisture content and some type of lifting action. Lifting  of warm air will not necessarily cause free convection. The  air may be lifted to a point where the moisture condenses  and clouds form. These cloud layers, however, will be  stable if the level of free convection has not been reached  by the lifting. Conversely, it is possible for dry heated air  to rise convectively without the formation of clouds. In this  condition, turbulence might be experienced in perfectly  clear weather. Cumulonimbus cloud formations require a  combination of conditionally unstable air, some type of lifting  actions, and high moisture content. Once a cloud has formed,  the latent heat of condensation released by the change of state  from vapor to liquid tends to make the air more unstable.  Thunderstorms over the ocean are most common during the  night and early morning. They frequently occur offshore  when a land breeze is blowing toward the water. The cool  land breeze is heated by the warmer water surface, which  results in sufficient convection to produce thunderstorms.  After sunrise, heating of the land surface reverses the airflow  (sea breeze). The thunderstorms then dissipate over the water,  but they may re-form over the warmer land surface. As an  example, the air mass weather that exists in Florida combines  both types of convective thunderstorms. Circulation around  a semipermanent high pressure system off the southeastern  United States (Bermuda high) carries moist ocean air over  the warm land surface of the Florida Peninsula. At night,  Some type of external lifting action is necessary to bring  the warm surface air to the point where it will continue to  rise freely (the level of free convection). For example, an air  mass may be lifted by thermal convection, terrain, fronts, or  convergence.  By no means is the information contained here a complete  discussion of all the weather information and factors affecting  balloon flight. There are many resources available, both  Summary 4-27 Minimum Factors  Air Mass Thunderstorms