(UPDATE 11:20 p.m. CDT March 23: Frustratingly quiet out there though I did get to hear my first saw-whet owl. Updated forecast still calls for a minor storm now through 1 a.m. but also adds from 4-7 a.m. tomorrow morning. Still mostly clear in Duluth, Minn. but no aurora visible.)
The forecast still looks good for tonight for possible auroras, but let’s break it down so you’ll know what to expect. First off, last night and this morning there has been zero activity. Between 10 a.m. and 1 p.m. today, the Kp index, a measure of magnetic activity in the upper atmosphere, is forecast to reach “5.” Kp can range form “0” to “9.” The higher the number the more likely we are to see northern lights.
When the Kp reaches 5, skywatchers in the northern regions of the northern border states can generally see the aurora, but it’s on the quiet side — a low bright arc with few faint rays dancing about late in the evening. Kp 5 is the equivalent of a G1 or minor geomagnetic storm.
When the index reaches 6, it becomes a moderate or G2 storm. That means the aurora is more widespread and visible across New York state, Michigan, Wisconsin, Minnesota, North Dakota and so on. You might even see a little from northern Illinois.
Next, let’s makes sense of the forecast times. They’re in Universal Time. To convert to Central Daylight Time, we subtract 5 hours, so 15-18 UT = 10 a.m. to 1 p.m. Central Time. Subtract 4 for Eastern, 6 for Mountain and 7 for Pacific.
The storm strengthens to the G2 level from 18-21 UT or 1-4 p.m. Central Time, the middle of this afternoon. Perfect for northern European observers but not for us in the U.S. because the sun’s still up! Between 00-03 UT on March 24 — or 7-10 p.m. Central Time tonight (remember you have to subtract 5 hours) — activity declines to Kp 5 (minor storm) and stays that way through 1 a.m. (06 UT) Sunday morning.
Almost anything can happen when it comes to the aurora. I’ve seen it appear right on schedule, show up early or late or not at all! Aurora chasers know how capricious the “lights” can be. If you don’t already have a good aurora-viewing spot, take a drive today to find a field or road away from city lights with a wide open view to the north. Then check the northern sky tonight as soon as it gets dark. Go out again an hour later for another look. If you’re dedicated you’ll do this till midnight. If you’re really, really dedicated you’ll set your alarm for yet another look around 2-3 a.m. tomorrow morning.
For photography, you’ll need a tripod and a camera that can take at least a 15-second-long time exposure. A wide angle lens is best. Set both the lens and camera to manual (M), focus carefully on a bright star, set the ISO to 1600 and expose at your widest lens setting (f/2.8-4.5) for 15-30 seconds. That’ll at least get you in the ballpark. You’ll find more tips here.
Thankfully, the moon won’t rise until around 10:30-11 p.m., so we’ll have a decent amount of dark sky for the aurora to do its thing — should it appear. Good luck and clear skies!