From the National Weather Service:

...NEAR FREEZING TO SUB-FREEZING TEMPERATURES EXPECTED BY EARLY
TUESDAY MORNING...
.AFTER AN EXTENDED STRETCH OF UNSEASONABLY WARM WEATHER THE LAST
TWO WEEKS MANY PLANTS HAVE BUDDED OUT ACROSS THE AREA. THIS EARLY
BUDDING ESPECIALLY WITH FRUIT TREES MEANS PLANTS ARE VERY
VULNERABLE TO FREEZING CONDITIONS.
COLD HIGH PRESSURE IS FORECAST TO BUILD SOUTHEASTWARD OUT OF
CANADA TODAY AND INTO THE EASTERN GREAT LAKES BY TUESDAY. MOSTLY
CLEAR TO PARTLY CLOUDY SKIES AND LIGHT WINDS TONIGHT WILL LEAD TO
RAPID TEMPERATURE DROPS WITH LOWS AROUND THE FREEZING MARK OR
POTENTIALLY COLDER FORECAST BY EARLY TUESDAY MORNING.
...FROST ADVISORY IN EFFECT FROM 1 AM TO 10 AM EDT TUESDAY...
THE NATIONAL WEATHER SERVICE IN INDIANAPOLIS HAS ISSUED A FROST
ADVISORY...WHICH IS IN EFFECT FROM 1 AM TO 10 AM EDT TUESDAY.
* TIMING: TEMPERATURES FALLING TO THE LOW TO MID 30S FOR SEVERAL
HOURS EARLY TUESDAY MORNING.
* IMPACTS: THE GROWING SEASON ACROSS CENTRAL INDIANA IS ADVANCED
WITH THE RECENT PROLONGED PERIOD OF WARM WEATHER. SENSITIVE
OUTDOOR PLANTS MAY BE DAMAGED OR KILLED IF LEFT UNCOVERED.