Weather World
Newcastle, IL Weather Forecast
Quick Weather Clicks
Settings
Sun & Moon
Newcastle Weather Forecast
| TODAY | TONIGHT | WEDNESDAY | WEDNESDAY NIGHT | THURSDAY | THURSDAY NIGHT | FRIDAY | SATURDAY | SATURDAY NIGHT | SUNDAY | SUNDAY NIGHT | MONDAY |
 |  | |  | | | | | |  |  |  |
| Sunny | Mostly Clear | Sunny | Partly Cloudy | Sunny | Mostly Clear | Mostly Clear | Mostly Clear | Partly Cloudy | Partly Cloudy | Chance of Showers | Chance of Showers |
| Hi: 99°FHi: 37°C | Lo: 71°FLo: 22°C | Hi: 99°FHi: 37°C | Lo: 71°FLo: 22°C | Hi: 99°FHi: 37°C | Hi: 95°FHi: 35°C Lo: 71°FLo: 22°C | Hi: 95°FHi: 35°C Lo: 71°FLo: 22°C | Hi: 95°FHi: 35°C Lo: 71°FLo: 22°C | Hi: 90°FHi: 32°C Lo: 71°FLo: 22°C | Hi: 90°FHi: 32°C Lo: 71°FLo: 22°C | Lo: 65°FLo: 18°C | Hi: 81°FHi: 27°C |
| POP: 30% | POP: 30% |
POP = Probability of Precipitation.
Weather Outlook Updated: 447 AM CDT Tue Sep 15 2026 
Newcastle Radar Loop
Use the map search tool if you want to place a location marker on the radar map...
Newcastle Weather Map
Newcastle Quick Facts
Newcastle Forecast Discussion
Meteorlogic Glosserator
Instant definitions for any meteorological term.
Instant definitions for any meteorological term.
Issued: 531 AM CDT Tue Sep 15 2026
Key Messages
- A dangerous late season heat wave with high temperatures near or at record levels will begin today and continue through most of the week.
- A Heat Advisory will be in effect this afternoon through Wednesday evening for the entire area. The Heat Advisory may need to be extended to Thursday or Friday as well.
- Cooler and less humid conditions will arrive Sunday and Monday, along with a 20 to 40% chance of showers and thunderstorms on both days.
Discussion
... Issued at 1052 PM CDT Mon Sep 1...