As you indicate, the weather can often play a role in aggravating (or sometimes helping) with asthma
symptoms. Asthma is part of a family of disorders known as reactive airway disease--and as the name suggests, the symptoms of an asthma attack are caused by overactive airways. Many different things can be triggers for the constriction of the airways that causes shortness of breath and wheezing in asthma, and weather conditions can be one of them. The important thing to remember is that what sets off your asthma may be different than that of someone else, so if you can identify a pattern for your symptoms it is important for you to make a note of this.
Studies in the emergency room have shown that often extreme weather (very hot or very cold) can lead to an increase of asthma symptoms in the community. Hot, dry air can often do the same thing--it sounds as though this may be true for you. In addition, changes in barometric pressure (often caused by storm fronts, such as the thunderstorms of the summer); extreme wind (thought to increase the number of fungal spores in the air); or hot, humid air (increasing mold spores, possibly combining with chemicals in the air to increase the concentration of pollutants) can all trigger asthma exacerbations.