Last month, the strongest geomagnetic storm in decades brought the northern lights to Washington State. The storm was set off by coronal mass ejections released by a sunspot cluster. Since it takes the sun 27 days to rotate completely, that cluster will be facing Earth again in early June, and as of now, it's still active.
According to Erica Grow Cei, a spokesperson for the National Weather Service, National Oceanic and Atmospheric Administration forecasters picked up moderate solar flares from the sunspot cluster earlier this week.
"It is not common for sunspot groups to survive a full 27-day rotation and still be a decent sunspot group upon return," Cei said in an email to McClatchy. "This active region has already proven to still be a flare producer with its recent R3 level flare on May 27th, before that section of the sun rotated back into Earth-view."
How likely is an aurora in Washington?
If the cluster continues to produce at flares that strength, there's a strong possibility that it sets off a coronal mass ejection powerful enough to cause an aurora visible from the northern U.S. But how likely is it that it doesn't die down over the coming days?
Cei said that NOAA's Space Weather Prediction Center hasn't seen any indication that the sunspot cluster is slowing down just yet.
"Our team at SWPC is forecasting solar flares from this cluster over the next couple of days. If the cluster continues to be active, the possibility of an aurora-generating CME facing toward Earth will increase."
Not all solar flares are accompanied by CMEs, though. So even if the flares continue, there's no guarantee of an aurora.
When would the June aurora be?
June 6 will be the 27th day since May's G5 storm, so the sunspot will be facing Earth once again. It coincides with a new moon, meaning if the sunspot does produce strong enough solar flares, the sky figures to be dark enough to see the resulting aurora. Solar activity tracker spaceweatherlive.com, meanwhile, says the chances of an aurora will be highest between June 8 and 12, based on NOAA data.
But the lights could even be visible before the sunspot faces Earth directly. NOAA has already issued a G2 storm watch for this weekend. The prediction only mentioned the possibility of an aurora being visible between New York and Idaho, though, so Washington is likely out of luck. According to the SWPC's aurora viewing guide, a storm needs to reach G3 levels in order to be visible in most of Washington.
Cei said that it's difficult to predict exactly when a sunspot will release a CME and how strong it will be until right before it hits Earth.
"At this time, it is not possible to forecast the strength of a CME until it is observed, which means we will not know the extent of an aurora resulting from a CME until a day or two before its arrival," Cei said.
For now, keep an eye on SWPC's experimental aurora dashboard for up-to-date aurora predictions, and check a few extra times in the days before and after June 6.
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