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Altamont Reservoir, IL Weather Forecast
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Altamont Reservoir Weather Forecast
| TODAY | TONIGHT | SATURDAY | SATURDAY NIGHT | SUNDAY | SUNDAY NIGHT | MONDAY | TUESDAY | WEDNESDAY | WEDNESDAY NIGHT | THURSDAY |
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| Patchy Fog | Chance of T-Storm | Sunny | Clear | Sunny | Partly Cloudy | Partly Cloudy | Partly Cloudy | Partly Sunny | Partly Cloudy | Sunny |
| Hi: 81°FHi: 27°C | Lo: 65°FLo: 18°C | Hi: 81°FHi: 27°C | Lo: 61°FLo: 16°C | Hi: 80°FHi: 27°C | Hi: 81°FHi: 27°C Lo: 61°FLo: 16°C | Hi: 81°FHi: 27°C Lo: 61°FLo: 16°C | Hi: 81°FHi: 27°C Lo: 61°FLo: 16°C | Hi: 85°FHi: 29°C | Lo: 65°FLo: 18°C | Hi: 85°FHi: 29°C |
| POP: 20% |
POP = Probability of Precipitation.
Weather Outlook Updated: 637 AM CDT Fri Aug 21 2026 
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Altamont Reservoir Forecast Discussion
Issued: 558 AM CDT Fri Aug 21 2026
Key Messages
- A Slight Risk of severe thunderstorms exists this afternoon/evening north of a line from Beardstown to Lincoln to Gibson City. Hail (15%), wind (15%), and tornado (2%) threats will exist in this area, with lower probabilities further south.
Discussion
... Issued at 215 AM CDT Fri Aug 21 2026
Weak high pressure over IL this morning will give way to a weak cold front tonight along with an upper level wave. With CAPEs of 2000-3000 J/kg and shear around 30-35 kts, severe storms will be poss...