Illinois · 5 towns compared
Northern lights in Illinois: tonight’s chance
NOAA names Illinois in its description of a strong storm, and that is the level most of the state needs.
Tonight at Chicago, IL
…
Reading the SWPC Kp forecast and the cloud forecast…
| Kp forecast during the dark hours | not yet forecast |
|---|---|
| Kp needed here | 6.7 (G3 strong) |
| Cloud cover in the dark hours | loading |
| Dark sky (Sun 18° down) | 7:44 PM to 5:29 AM CDT |
| Moon | 13% lit |
| Right now, OVATION (30 to 90 min) | loading or unavailable |
| Magnetic latitude (AACGM) | 51.3° |
Hour by hour, CDT
7 PM
Kp –
– ☁
No
8 PM
Kp –
– ☁
No
9 PM
Kp –
– ☁
No
10 PM
Kp –
– ☁
No
11 PM
Kp –
– ☁
No
12 AM
Kp –
– ☁
No
1 AM
Kp –
– ☁
No
2 AM
Kp –
– ☁
No
3 AM
Kp –
– ☁
No
4 AM
Kp –
– ☁
No
5 AM
Kp –
– ☁
No
6 AM
Kp –
– ☁
No
Rules checked · Built by Radif Partners · How the answer works
- Kp to see it from Chicago
- 6.7
- Storm level needed
- G3 (Strong)
- Kp for aurora overhead
- 7.4
- Most clear dark hours
- September
Illinois is the state NOAA uses to describe a strong geomagnetic storm: at G3 (Strong), the scale says aurora has been seen as low as Illinois and Oregon. The thresholds computed here agree. Rockford and Chicago, in the north of the state, sit near 51.3 degrees magnetic latitude in the AACGM model and need about Kp 6.7; Peoria needs Kp 6.9, Champaign Kp 7.1 and Springfield about Kp 7.1. South of the capital the bar keeps rising, toward the severe storms that only come a few times in a solar cycle. Darkness and weather help more than the map. In Peoria, NASA POWER cloud averages range from 44% in September to 69% in December, and September and October give the most clear dark hours. The tool opens on Chicago; type any Illinois town or ZIP code for its own hourly answer.
The state on NOAA's storm scale
Illinois has an unusual place in aurora writing: it appears by name on the NOAA space weather scale. The G scale describes a G3 (Strong) storm as one during which aurora has been seen as low as Illinois and Oregon, and that line matches what this site computes for the state. The north, from Rockford across to the Chicago suburbs, needs about Kp 6.7. The middle of the state, Peoria and the Illinois River valley, needs Kp 6.9, and the prairie around Champaign and Springfield about Kp 7.1. In other words, a G3 storm reaches the top third of Illinois comfortably and the center barely.
Because those thresholds sit so close together, the forecast's three-hour blocks decide more than the map does. A storm that touches Kp 7 for a single block in the early evening may light the sky over Rockford for an hour and never reach Springfield's horizon; one that holds that level past midnight gives the whole northern half of the state a turn.
How dark, how clear: one town, one month
Hours of full darkness on the 15th
10.9 h
| Dark sky | 6:15 PM to 5:11 AM |
| Including nautical twilight | 12.0 h |
| Mean cloud amount (NASA POWER) | 59% |
| Clear dark hours on an average night | 4.4 h |
Computed for 2027; the hours move by a few minutes from one year to the next.
Prairie darkness versus the Chicago dome
The Chicago metro produces one of the largest light domes in the country, and it spreads far into the surrounding counties. For aurora, that glow is the main problem in the northeast of the state: it brightens the very part of the sky where a low display would show. West of the Fox River the situation changes quickly. The farmland of north central Illinois is flat and sparsely lit, and the northwest corner, around the hills near Galena and the Mississippi bluffs, is darker still. From there, a storm that reaches Kp 6.7 has a clean northern horizon to rise from.
Central Illinois has the same open land, with a slightly higher threshold. The Chicago page covers the escape routes from the city, and the Wisconsin page shows how quickly the bar drops north of the state line.
When the Illinois sky clears
Illinois sits in the path of many winter storm systems, which keeps the cold months grey: December is Peoria's cloudiest month at 69%. Early autumn is the friendlier season, with drier air, nights that lengthen quickly after the equinox and a cloud amount near 44% in September. For a G3 storm, which may last only a few hours, being ready on a clear autumn evening matters more than waiting for the longest nights. The storm scale guide explains how often each storm level occurs.
Kp needed across Illinois
| Town | Magnetic latitude | Kp to see it | Kp overhead | Storm level |
|---|---|---|---|---|
| Rockford | 51.7° | 6.7 | 7.2 | G2 (Moderate) |
| Chicago | 51.3° | 6.7 | 7.4 | G3 (Strong) |
| Peoria | 50.3° | 6.9 | 7.9 | G3 (Strong) |
| Champaign | 49.7° | 7.1 | 8.2 | G3 (Strong) |
| Springfield | 49.4° | 7.1 | 8.3 | G3 (Strong) |
Darkness and clouds by month in Chicago
| Month | Dark hours | Dark sky, 15th | Mean cloud | Clear dark hours |
|---|---|---|---|---|
| January | 11.2 h | 6:23 PM to 5:37 AM | 71% | 3.3 h |
| February | 10.2 h | 6:57 PM to 5:11 AM | 70% | 3.1 h |
| March | 9.0 h | 8:30 PM to 5:28 AM | 66% | 3.1 h |
| April | 7.3 h | 9:12 PM to 4:28 AM | 63% | 2.7 h |
| May | 5.5 h | 10:00 PM to 3:33 AM | 64% | 2.0 h |
| June | 4.4 h | 10:39 PM to 3:03 AM | 56% | 1.9 h |
| July | 5.0 h | 10:27 PM to 3:25 AM | 48% | 2.6 h |
| August | 6.6 h | 9:36 PM to 4:14 AM | 48% | 3.5 h |
| September | 8.4 h | 8:35 PM to 4:57 AM | 46% | 4.5 h |
| October | 9.8 h | 7:41 PM to 5:31 AM | 58% | 4.1 h |
| November | 11.0 h | 6:06 PM to 5:04 AM | 63% | 4.0 h |
| December | 11.5 h | 6:01 PM to 5:31 AM | 73% | 3.2 h |