Dean Lerner's reply:
Your question shows maturity in your teaching. Observing and assessing the moods and conditions of students is universal among alert teachers. Indeed, the weather and atmosphere can affect our moods and energy levels significantly, as do other factors, such as the time of day and the season. Students may come to class physically tired after a day's work, mentally fatigued, or simply feeling lazy.
There is no set formula on how to determine the best course to take. A teacher's response must be guided by analysis, experience, and intuition.
The situation you describe—a rainy, gray day, low energy, and lethargic students—implies the need to awaken, refresh, and balance the students. One way to quietly settle and refresh the body and mind, and get students moving, is to begin the class with Supta Virasana (Reclining Hero Pose) and Supta Baddha Konasana (Reclining Bound Angle Pose)—and, depending on time, Matsyasana (Fish Pose)—followed by Uttanasana (Standing Forward Bend) and Adho Mukha Svanasana (Downward-Facing Dog Pose). The latter two poses bring a fresh supply of blood to the brain, draw the mind into the present moment, and create an alert awareness. Refreshed by this new perspective, your students will be ready to explore the remainder of class in whatever direction you wish to take it.
Certified Advanced Iyengar instructor Dean Lerner is co-director of the Center for Well-being in Lemont, Pennsylvania and teaches workshop across the United States. He is a longtime student of B.K.S. Iyengar and served a four-year term as president of the Iyengar National Association of the United States. Known for his ability to teach yoga with clarity and precision, as well as warmth and humor, Dean has conducted teacher training classes at Feathered Pipe Ranch in Montana and other locations.