Extended weather forecasts-- buncha hooey?

[ho'ard]

"Extended forecast" for next Saturday says storms, although adjacent days are fine. That's a week from today.
Are these reports actually based on something, or is it just entertanment?

Thursday:
Partly Cloudy
High 82°F
Low 71°F
Precip. 20 %

Friday
Partly Cloudy
High 86°F
Low 73°F
Precip. 20 %

Saturday
Scattered T-Storms
High 79°F
Low 66°F
Precip. 40 %

Sunday
Sunny
High 79°F
Low 64°F
Precip. 20 %

Monday
Mostly Cloudy
High 76°F
Low 61°F
Precip. 20 %