Hi patobert,
Welcome to alli fitness forum and thanks for writing! Congratulations on your weight loss! You should be very proud of your progress!
So, to address your question.. It isn't unusual at all to experience a short-term plateau when beginning any weight-loss or exercise program. There are many, many factors that can influence the # on the scale from day to day, even hour to hour. Things such as time of day, hormonal fluctuations (men and women), hydration level, the amount and type of physical activity performed the day before, and more. It is therefore, important that you weigh once a week, at the same time of day. That doesn't ensure a error-proof measurement, but gives more consistency to it.
Additionally, the smaller you get (the less you weigh), the more challenging it is to take the pounds off. This is b/c your body requires less calories (energy) to function all day long, therefore, you must continue to adjust your caloric intake, as well as activity to make up for the difference. The key to this is to continue performing both cardiovascular activities such as walking, hiking, biking, swimming, etc. as well as strength training. Strength training is going to allow you to maintain/increase lean muscle mass as you lose weight (fat). This is so important b/c lean muscle requires more energy (calories) than fat mass and therefore really ramps up your metabolism, even at rest.
Continue with your walking program! The walking is not to blame for the plateau, and is only a positive to your healthy lifestyle in every way. You will gain heart-healthy benefits, increase your fitness level and burn extra calories! So, keep it up!
Do begin to incorporate a strength training program into your weekly regimen 2-3 times per week for 25-35 minutes each session. Go to "my activity" and click on "strength training log" to view animated demos for each strength training exercises.
Best of luck to you and keep us posted with your progress!
Your friend in fitness,
Kelli