Riyadh’s climate has a greater difference between winter and summer temperatures than elsewhere in the Kingdom. Riyadh has practically no humidity, making summers especially dry and dusty. Annual rainfall averages 2 to 4 inches, usually concentrated in a few torrential rainfalls in early spring. Winters produce moderate daytime temperatures from November through February. Evenings are sometimes cool enough to require residential heating.
Jeddah, the commercial center, has a tropical climate — mild in winter and hot and very humid in summer. Summer lasts 8 to 10 months, with temperatures moderating in November. Relief from the heat often comes at sunset when sea breezes arrive. Except on the few occasions when it rains, the sun shines daily. Winter is comparable to the spring and summer seasons of resorts on the Mediterranean Sea.
Dhahran’s climate, like that of Jeddah, is very humid, 60% – 90%, with summer lasting from April through October. The average maximum shade temperature in July and August is 110 °F, with "in sun" temperatures up to 150 °F. From December to April, it is cooler and pleasant, with indoor heating required at times, especially in the areas north of Dhahran.
Rainfall in both Jeddah and Dhahran is sparse, about 3 – 4 inches a year concentrated in a few heavy showers during fall and spring.