Will We See an Aurora Tonight?

The Space Weather Prediction Center (SWPC) is getting pretty excited about the odds of a Northern Lights show tonight (Friday night).  If you're like me, you've seen these alerts before, only to be disappointed by the lack of an aurora.  But tonight might be different.

First, I'll start with the Kp Index that the SWPC folks track.  I'll spare you the details.  What you want to know is that this index has had a dramatic jump on Friday morning.  Values over 6 typically (but not always) produce an aurora in the Inland NW.  This morning the value has jumped to nearly 8, and 8.5 this afternoon.



SWPC has issued a G4 Watch for tonight.  The last time they did this was in 2005.  So that should tell you that this is an unusually strong event and the folks at SWPC have high confidence.

Here's a map from SWPC showing the probability of an aurora.  For the US-Canada border, the odds are very high.  For Washington and North Idaho, the odds are a little lower, but still high.  And this map typically doesn't take into account that if you're in Spokane, you're usually seeing the aurora far to the north.


SWPC expects the geomagnetic storm to peak between 11pm Friday and 2am Saturday.  That said, the Kp of nearly 8 this morning was higher than they were forecasting.  I'm no space weather expert, but it could be that the event will either peak earlier than they previously thought, or perhaps it's stronger than they expected.

So will the weather cooperate?  In a word, yes.  The computers are forecasting some high clouds across southern BC in the evening, migrating over to western Montana overnight.  Here's the evening forecast from the GFS (U.S. model).  Note: grey represents a low chance of clouds, blue a high probability of clouds, and white means no clouds.


And here's the 2am forecast.


So there could be some wispy high clouds, but probably not enough to have any great impact on viewing the aurora.

As for the upcoming weather, our warm and sunny weekend will give way to slightly cooler (still in the 70s) and breezy weather next week.  There are very low chances of any rain showers.  By about the 20th of May the pattern may be changing to a bit cooler and wetter, but that's 10 days away.






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