Forecast tools · live SWPC data
Aurora forecast: the next three nights for your town
The SWPC forecast runs about three days ahead in three-hour blocks. Here each block meets your sky: darkness, clouds and the Kp your place needs.
Tonight at Minneapolis, MN
…
Reading the SWPC Kp forecast and the cloud forecast…
| Kp forecast during the dark hours | not yet forecast |
|---|---|
| Kp needed here | 5.9 (G2 moderate) |
| Cloud cover in the dark hours | loading |
| Dark sky (Sun 18° down) | 8:08 PM to 5:50 AM CDT |
| Moon | 13% lit |
| Right now, OVATION (30 to 90 min) | loading or unavailable |
| Magnetic latitude (AACGM) | 54.2° |
Tonight
…
no Kp forecast covers this night yet
Kp max – · clouds – · dark 8:08 PM to 5:50 AM
Wed, Oct 14
…
no Kp forecast covers this night yet
Kp max – · clouds – · dark 8:07 PM to 5:51 AM
Thu, Oct 15
…
no Kp forecast covers this night yet
Kp max – · clouds – · dark 8:05 PM to 5:52 AM
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
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An aurora forecast is really two forecasts stacked. The first is the planetary Kp forecast of the NOAA Space Weather Prediction Center, a value from 0 to 9 for each three-hour block of Universal Time over roughly the next three days, revised as new solar wind data and solar images come in. The second is your local weather, because the best storm of the year is worthless under overcast. This page puts both side by side for tonight, tomorrow night and the night after, at the place you choose. A night gets a yes when at least one hour of full darkness has a forecast Kp at or above the value your magnetic latitude needs and a sky forecast at 30% cloud or less. Marquette needs about Kp 5.1, Bismarck about 5.3, so the same SWPC table can mean three yes nights in one town and none in the next.
Reading three nights at once
The three cards under the tool summarise each night with one word, the best hours, the highest Kp forecast while it is dark, and the average cloud cover over those hours. Open a night in the selector of the tonight page to see it hour by hour. The point of three nights is choice: if tonight is a maybe under broken cloud and the night after a yes with a clear forecast, the second is the one worth staying up for, especially at the edge of your range.
The Kp blocks come straight from the SWPC data service (planetary K-index forecast, JSON), which carries observed values for the past week, an estimate for the current block, and predictions for the next blocks. The tool uses the predicted values for future hours and the estimated value for the current one. Nothing is smoothed or adjusted: if SWPC predicts Kp 4.67 for 03 to 06 UT, every hour inside that block carries 4.67, which SWPC labels 5- and which already counts as a G1 storm on the NOAA storm scale.
Why a Kp forecast misses
Most strong forecasts follow a coronal mass ejection seen leaving the Sun one to three days earlier. Its speed is estimated from coronagraph images, so the arrival time carries an uncertainty of several hours, and the strength of the storm depends on the direction of the magnetic field inside the cloud, which nobody can measure until it passes the monitors at L1, 1.6 million kilometers upstream. A field pointing north can deliver a fast cloud and almost no aurora. The solar wind and Bz guide explains what to watch on the night itself.
Coronal hole streams are easier: the Sun rotates in about 27 days, so a stream that brought Kp 5 last month often returns, which is what the 27-day outlook anticipates. Those storms rarely go beyond G1 or G2, but they are punctual.
Clouds three days out
For US places the tool reads the hourly sky cover of the National Weather Service API for the forecast grid cell that holds your coordinates; elsewhere, the cloud fraction of MET Norway. Weather models are reliable on the broad picture a day or two ahead and weaker on the exact hour a front clears. A night announced overcast that clears at 1 am is common around the Great Lakes in autumn. If you can see stars, set the cloud selector to clear and the answer follows your sky instead of the model.
What this forecast does not know
It does not know your horizon: a ridge, a forest or city glow to the north can hide a display that is low in the sky, which is where it sits when your place is at the edge of the oval. It does not know local light pollution, and it cannot predict substorms, the bursts of activity that can light up a sky for twenty minutes on a night forecast at Kp 3. That last point cuts both ways, and it is the reason the current hour also looks at OVATION, shown on the live aurora map.