How To See Auroras
The first thing to know is the sun rotates once every 27 days or so(evidently 26 in the center.....34 at the poles). So if you have an active sunspot on the face of the sun it will cross to the other side in about two weeks if it starts at the edge. You basically need one facing Earth, to some degree, to flare and shoot out a CME or coronal mass ejection. The thing is you can also have a long filament eruption that doesn't need a spot.
http://www.spaceweather.com/ has a lot of the information you want on the left hand side. The current sun image is there for instance and usually some text about the spots. You need spots that are unstable. They have positive and negative areas and when they become intermixed they can snap and cause the big explosions. So first step is just knowing what is on the sun and how unstable they are.
http://www.solen.info/solar/ These guys have good daily updates describing the spot behavior at the time, as well as CME's etc. So in this first step it is as simple as glancing at that from time to time to see how things are currently behaving.
Solar flares and x-rays
The other thing to look at for the heads up of any solar flares, is the current x-ray plot. The one above from November 2004 before a big aurora event. If you get a big solar flare from these sunspots, it will show up basically immediately. So once you have established you have active spots or unstable ones, next stop is here. Heck you can look here to see if they are flaring. You can have one that is very unstable and has been for a while, that also hasn't flared either. But soon as it flares it will show on here. Just note the vertical dashed lines above the date is the date at 0z or 0 UTC. Spring through summer for instance in the central time zone here 0z is 7pm. When the time changes again it is 6pm.
So once you have a big flare you'll need to know two things. What location on the sun did it come from and did it produce a CME and a good one at that. Was it some spot near the edge, which is less likely to be Earth directed, or something more in the middle. Could have even been a filament erupting. The good news is that any CME takes a lot longer to reach here than the time it takes to show it happened on this plot, so there's time to find out where the flare came from. I'd say a lot of CME's take 36-54 hours to reach here. Some longer some shorter. 36 hours would be a damn fast CME. They can go even faster though. Generally speaking you have a couple days.
So those big peaks on the graph above were flares. Not all flares send out CMEs(coronal mass ejections) though. Notice on those peaks the difference in fall off time. Take the first red jump on the left for instance. Bam it spikes up right away as the flare happens. Then look at the time it takes to fall off. Those are hours. Next one on the November 5th the same way. The one above M level, middle of the 5th, falls off pretty fast. When you see them fall off real fast, they are often "impulsive" flares and less likely to have a CME associated with them. The longer the fall off the better and more likely a CME was sent off. Think of it as a loud longer booooom.
Also there is an 11 year solar cycle that peaks and wanes over that time. At the end of 2012 we are climbing closer and closer to the peak, so the sun activity picks up.
Coronal mass ejections
Here is a capture of a CME. A big and bright nice CME which is not heading to Earth but being shot out into space another way. But anyway, once you have active spots established and some flares showing up on the x-ray plots, it's time to find out where the CME came from on the sun and if it is headed to Earth and how nice and bright it looks or how fast it is moving as well.
One way is NOAA puts out an update once a day at 22z(5pm central time). http://www.swpc.noaa.gov/forecast.html Those can be fairly useful. I actually kinda prefer what these guys have to say a lot of the time. http://www.solen.info/solar/
Just like chasing storms though, it is best to just do all that you can yourself. http://sohowww.nascom.nasa.gov/data/realtime/gif/ Use the Lasco 2 and Lasco 3 gif animation links. They aren't real timely but they don't really need to be. Often if you see a big flare show up on x-ray plots, the animations will be updated far enough to include them within 6-12 hours. Just look at the flare on the x-ray plot and note the time/date. Then while watching the animations on there, stare at the date till just before that time. Then watch to see how the cme, if there was one, looks. Not as nice or useful, but a lot more timely initially are the stereo spacecraft images at the bottom here... http://stereo.gsfc.nasa.gov/beacon/ Those are on either side of the sun. There are also some ahead gifs on there to try and see where the flare originated from. The best view though is clearly Lasco 2 and 3 once they are updated far enough to include your flare.
The other useful thing now is to monitor the current watches and warning maps from NOAA. http://www.swpc.noaa.gov/alerts/warnings_timeline.html They will tack on big flare markers on there as well as watches for auroras, at various intensity levels. They will also tack on the impact marker. But no need to get that from them/there...
Solar CME impact
The next and really last thing in this order is await and monitor for the impact. There is a spacecraft called ACE which I guess is about 1 million miles out into space(the sun is 93 million). It monitors the solar wind and will register the shockwave front and CME before it reaches Earth, not long before. So say you had a CME off the sun a couple days prior and learn it should be here that night. Just refresh that page and watch those plots. It will be obvious something hit. Some hits are weak, some are strong. The velocity will jump up. Note the above is around 500 kilometers per second...really really fast. Many can be a lot higher than that yet. I've seen some good aurora shows in the 300's however and I've seen jack with it screaming at 900 km/s before too. I only value the wind ob so much. Density can be useful in gauging the amount of "stuff" in the cloud. Think about something like feather being shot out of something or say a bowling ball. Really want to knock Earth's magnetosphere out of whack, it should probably have some density to the CME. Then there is Bz, the best gauge after it hits. Evidently as a CME blasts off the sun it can have a lot of negative goodies for us, or it can also have more of a positive charged field with it. In order for the show to dip south into more southern latitudes, you are going to want a nice negatively dominated cloud. And apparently that is the biggest catch in forecasting all this. It doesn't seem anyone has a real good idea what kind of material is in the dang CME till it gets here.
So as far as gauging an impact, all I really do is base it off the Lasco 2 or 3 images of the CME. If it looks big, bright and nice, I'm pumped for the potential. Yet I have no clue if it contains the good stuff or the bad stuff till it gets here. I at least know by that, that it is of more substance than something weaker visually. Most people want to see big X flares or high level M flares. Man I've seen so many of those that look really great on Lasco and they wind up an utter dud, apparently with the wrong stuff. I've see two freaking amazing events from a low X and a high M though. I've seen auroras to weaker degrees a whole lot of times now. If I was ranking things, my 3rd, 4th, and 5th best shows were actually from measly C flares. So clearly, all this said, it's very much a guessing game even with all the data. Once you have something coming at you, the best thing is to just head on out as soon as it has arrived, which the plots and whatnot are great for that part.
KP index uselessness
Chasing auroras based off KP readings is useless and a waste. Sure if you see a current KP8 or KP9 I'd be flying out the door. But with all the other data before that point, you should have already been out the door by then anyway. The above for example is a 3 hour graph. An utter waste for chasing auroras. Even the places that offer the "current" or hourly ones are pointless. Usually you'll have already had an aurora outburst happen, then those come out right after. It might be completely over for you by that point. Ooops. So many times I've seen the best part happen while the KP deal is still at 4 or 5. Then eventually they bump it up to KP6-7-whatever. Then you sit there and don't see much at all. Lots of people will wait for the KP value to be high before bothering to head out. Not a good way to chase auroras. Like chasing tornadoes and waiting at home till a tornado warning is issued. I suppose it can work for the huge extreme and long lasting events. Too bad, because I think the average times KP9 is reached in a whole 11 year solar cycle is 4 times. So chop that to 2 if you want daylight/night odds involved. Then whatever your normal cloud issues are. Then there's the moon. But yeah, KP numbers are a waste for observing auroras.
The other thing is the outbursts are usually 15-20 minutes it seems. You can go from far north faint green arc to full blown high bright reds and back to faint far green auroras in 20 minutes. All while sitting with a KP4...and residing under the KP7 line here:
I'm just south of the KP7 line. This is a map where given the KP value the aurora is supposed to reside above. I've seen several shows at KP4 and even some at KP3. For chasing, it's pointless to base when you go out using KP values. KP values that are a 3hr average are the most useless version lol. If you want to see auroras, pretend KP values don't exist and go out. You can do a lot better going out when the Bz goes negative and then just watching.
Since the ACE spacecraft reading the solar wind obs is a million miles out, often when you see a big Bz drop south on there, any good change to the aurora show will often occur in another 20-40 minutes. We've noted this several times.