National Weather Service Forecast for: Johnston IA
Issued by: National Weather Service Des Moines, IA
Updated: 1:26 am CDT Jun 30, 2026
 
Overnight

Overnight: Partly cloudy, with a low around 77. South southwest wind around 10 mph, with gusts as high as 21 mph.
Partly Cloudy

 Tuesday

Tuesday: Mostly sunny, with a high near 94. Heat index values as high as 103. South southwest wind 8 to 15 mph, with gusts as high as 25 mph.
Mostly Sunny

 Tuesday
Night
Tuesday Night: A 30 percent chance of showers and thunderstorms, mainly before 10pm. Mostly cloudy, with a low around 75. South southwest wind 9 to 11 mph, with gusts as high as 21 mph. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.
Chance
T-storms then
Mostly Cloudy
 Wednesday

Wednesday: A 10 percent chance of showers before 7am. Mostly sunny, with a high near 93. Heat index values as high as 101. Breezy, with a south southwest wind 10 to 16 mph, with gusts as high as 26 mph.
Slight Chance
Showers then
Mostly Sunny
and Breezy
 Wednesday
Night
Wednesday Night: A 40 percent chance of showers and thunderstorms. Partly cloudy, with a low around 75. South southwest wind 9 to 14 mph, with gusts as high as 25 mph. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.
Chance
Showers then
Chance
T-storms
 Thursday

Thursday: A 30 percent chance of showers and thunderstorms. Mostly sunny, with a high near 92. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.
Chance
T-storms

 Thursday
Night
Thursday Night: A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 1am. Partly cloudy, with a low around 73. Chance of precipitation is 60%.
Chance
T-storms then
Showers
Likely
 Friday

Friday: A 30 percent chance of showers and thunderstorms before 1pm. Mostly sunny, with a high near 93.
Chance
T-storms

 Friday
Night
Friday Night: A 30 percent chance of showers and thunderstorms. Partly cloudy, with a low around 72.
Chance
T-storms
Lo 77 °F Hi 94 °F Lo 75 °F Hi 93 °F Lo 75 °F Hi 92 °F Lo 73 °F Hi 93 °F Lo 72 °F

Hazardous Weather Outlook
Extreme Heat Warning
 

Overnight
 
 Partly cloudy, with a low around 77. South southwest wind around 10 mph, with gusts as high as 21 mph.
Tuesday
 
 Mostly sunny, with a high near 94. Heat index values as high as 103. South southwest wind 8 to 15 mph, with gusts as high as 25 mph.
Tuesday Night
 
 A 30 percent chance of showers and thunderstorms, mainly before 10pm. Mostly cloudy, with a low around 75. South southwest wind 9 to 11 mph, with gusts as high as 21 mph. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.
Wednesday
 
 A 10 percent chance of showers before 7am. Mostly sunny, with a high near 93. Heat index values as high as 101. Breezy, with a south southwest wind 10 to 16 mph, with gusts as high as 26 mph.
Wednesday Night
 
 A 40 percent chance of showers and thunderstorms. Partly cloudy, with a low around 75. South southwest wind 9 to 14 mph, with gusts as high as 25 mph. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.
Thursday
 
 A 30 percent chance of showers and thunderstorms. Mostly sunny, with a high near 92. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.
Thursday Night
 
 A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 1am. Partly cloudy, with a low around 73. Chance of precipitation is 60%.
Friday
 
 A 30 percent chance of showers and thunderstorms before 1pm. Mostly sunny, with a high near 93.
Friday Night
 
 A 30 percent chance of showers and thunderstorms. Partly cloudy, with a low around 72.
Independence Day
 
 A 40 percent chance of showers and thunderstorms before 1pm. Mostly sunny, with a high near 92.
Saturday Night
 
 A 40 percent chance of showers and thunderstorms. Partly cloudy, with a low around 70.
Sunday
 
 A 40 percent chance of showers and thunderstorms. Partly sunny, with a high near 88.
Sunday Night
 
 A 30 percent chance of showers. Partly cloudy, with a low around 67.
Monday
 
 Mostly sunny, with a high near 88.

 

Forecast from NOAA-NWS for Johnston IA.