Astro Bob: Strong geomagnetic storm, auroras forecast Aug. 17-18
A pair of solar blasts are expected to punch up bright auroras across the much of the upper U.S. and Canada Wednesday night.
Wow, this looks good. We have a solid forecast for northern lights Wednesday night through Thursday dawn, August 17-18. The first wave of the storm hit earlier this morning, with the grand slam expected to arrive early Wednesday night.
Solar forecasters point their collective finger at a CME (coronal mass ejection) that erupted back on August 14 as the primary cause, amplified by a recent coronal hole, a high-speed wind of material streaming from a gap in the sun's atmosphere.
NOAA's Space Weather Prediction Center (SWPC) forecasts a strong geomagnetic storm reaching the G3 level on a 1 to 5 scale of increasing intensity. While that won't pose a threat to power grids and satellites it does mean that folks living as far south as Illinois and Oregon may finally get their chance to see a northern lights show.
Aurora is likely to show as soon as evening twilight ends across northern Maine, Minnesota, Michigan, Wisconsin and North Dakota. It should intensify after 10 p.m. local time and remain strong through 2 a.m. before declining to a moderate (G2) storm before dawn. Based on past aurora behavior and the latest forecast, peak activity will likely be from about 11 p.m. to 1 a.m. local time.
More good news! The shock from the impact will be significant, with storming continuing at the moderate level through Thursday night, Aug. 18. Two nights in a row of aurora — can we be so lucky? Let's hope so!
Always there are caveats. Sometimes the best forecast storms blow by without even touching us. Or they arrive early during the daytime. You drive 100 miles, stay up late and see nothing. I try to remind myself that nature always has the upper hand and can be as predictable as capricious. Think of the aurora as more like a relationship, where compromise (clouds, failure to appear) helps us take things in stride. That said, I'm reasonably confident we'll have a wonderful show.
Watching the northern lights requires no special equipment, just your eyes and if you like, a chair. The only essentials are a dark sky to the north with as little city light pollution as possible and clear weather. Partly cloudy works, too.
My local forecast isn't looking great. We expect mostly cloudy skies with maybe some clearing around midnight. Like you, I listen to the National Weather Service forecast, but my favorite tool is Clear Sky Chart , which displays an hourly cloud forecast. Each hour is shown as a small, colored square. The darker blue the square, the clearer the sky. A white one indicates overcast.
If you click on a square, a map showing your location and the predicted cloud cover pops up. Go to the website, then click the Find a Chart link to the left, fill in your location, and you're ready to go. I like to check it several times a day for the latest prediction. If things look dire for your town, click the Within 180 miles link to check on other locations that may offer better weather prospects.
We always like to know what the moon's doing since its glare can compromise a delicacy like the aurora. Good news on that front, too. It rises Weds. night around 11 p.m. local time near last quarter phase and shouldn't pose much of a problem. In fact, it presents yet another scenic opportunity for skywatchers — if you're out late, the moon triples up with Mars the Pleiades star cluster. Keep an eye out for this pretty trio.
I hope you have clear skies. Much luck to you! I'll update the aurora's progress Wednesday night on my Facebook page.