Frost Dates

The following chart is based on weather data collected from 1971 to 2000.* Probabilities indicate the likelihood of experiencing 32 F on or after the given date in spring and on or before the given date in fall. Cities and towns listed are grouped by their location in the state from north to south. Within each group, cities are listed from west to east.

	Spring		Fall		Median Growing Season in Days
Location	50%	10%	10%	50%
Sioux Center	May 2	May 14	Sept. 19	Sept. 29	152
Spencer	May 2	May 12	Sept. 21	Sept. 26	154
Algona	May 2	May 12	Sept. 21	Oct. 2	158
Mason City	May 2	May 14	Sept. 20	Oct. 2	155
New Hampton	April 29	May 9	Sept. 23	Oct. 5	162
Decorah	May 5	May 23	Sept. 22	Oct. 4	152
Sioux City	April 27	May 10	Sept. 21	Oct. 4	160
Ida Grove	May 1	May 15	Sept. 18	Oct. 2	153
Fort Dodge	May 2	May 14	Sept. 21	Oct. 5	157
Iowa Falls	May 3	May 10	Sept. 20	Oct. 3	156
Waterloo	May 1	May 12	Sept. 20	Sept. 30	152
Manchester	May 3	May 15	Sept. 21	Sept. 30	148
Dubuque	April 25	May 9	Sept. 22	Oct. 6	164
Harlan	April 30	May 12	Sept. 23	Oct. 6	161
Guthrie Center	May 2	May 11	Sept. 21	Oct. 2	153
Des Moines	April 21	May 2	Sept. 29	Oct. 11	176
Newton	April 19	May 5	Sept. 27	Oct. 8	175
Williamsburg	April 27	May 13	Sept. 24	Oct. 7	162
Iowa City	April 14	April 28	Oct. 1	Oct. 13	182
Le Claire	April 13	April 30	Oct. 4	Oct. 17	189
Red Oak	April 30	May 12	Sept. 18	Oct. 3	158
Creston	April 25	May 8	Sept. 21	Oct. 7	161
Osceola	April 23	May 9	Sept. 22	Oct. 10	169
Ottumwa	April 13	April 27	Oct. 2	Oct. 16	183
Mount Pleasant	April 21	May 6	Sept. 23	Oct. 10	174
Keokuk	April 8	April 19	Oct. 8	Oct. 22	198

* The data in this chart was provided by the Midwestern Regional Climate Center.