The prompts are on Carolyn Howard-Johnson's Sharing with Writers and Readers Blog and post the 15th of each month.
August 15th
Western Romance Writing Prompts for Writing Group Quick Writes Free Instant Download
September 15th Writing Prompts:
Dear 2020 from the Pandemic People Writing Prompts for the 15th
October 15th and Halloween Writing Prompts
Set One, Image Writing Prompts
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You might also like the following writing prompt freebies on the Wise Owl Factory blog.
14 Quick Writes or Flash Fiction Animal Theme Prompts Free