"Due to snowfall of between 5 and 10 cm and wind speeds of up to 60 km/h snowdrifts will build up,” reads the email.
It also recommends that people avoid using their cars due to the fact that in places streets “will be impassable.”
The weather warning is for the first two days of July.
The contents of the email came as a surprise to residents of the west German, state which is currently enjoying blue skies and temperatures of up to 35 degrees Celsius.
One Twitter wag from Bonn expressed his sympathy. "All of NRW is suffering under snow. Only little old Bonn has the sun. What an unfair world."
When the DWD were informed of the contents of the email the mystery was finally cleared up, reports the Rheinische Post.
A spokesperson said "We were testing a new warning system and unfortunately we sent a completely false report to subscribers.
"Naturally given the temperatures outside one need not worry about snow drifts."
Later on Wednesday the weather service apologized via Twitter.