DES MOINES, Iowa—The Nationals Weather Service changed the Freeze Watch issued Thursday to a Freeze Warning for Friday night to Saturday morning.  The move was not unexpected with the passage the a frontal boundary.

URGENT - WEATHER MESSAGE
National Weather Service Des Moines IA
1058 AM CDT Fri Oct 11 2019

...FREEZE WARNING REMAINS IN EFFECT FROM 10 PM THIS EVENING TO
9 AM CDT SATURDAY...

* WHAT...Sub-freezing temperatures as low as 28 expected.

* WHERE...Most of Iowa.

* WHEN...From 10 PM this evening to 9 AM CDT Saturday.

* IMPACTS...Frost and freeze conditions will kill crops, other
  sensitive vegetation, and possibly damage unprotected outdoor
  plumbing.

* ADDITIONAL DETAILS...Wind gusts of 15 to 25 mph will produce
  15 to 25 degree wind chill temperatures.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Take steps now to protect tender plants from the cold. To prevent
freezing and possible bursting of outdoor water pipes they should
be wrapped, drained, or allowed to drip slowly. Those that have
in-ground sprinkler systems should drain them and cover above-
ground pipes to protect them from freezing.