All types of sparking be it lightning, noisy motor, power lines, or a florescent light put out radio waves. Almost all forms of electrical impulse noise put out most of their energy (how strong they are) in 5 to 30 KHz range. But they also put out energy all the way to microwave frequencies.

Though as the frequency gets higher, the less energy from the spark exists at any given frequency or bandwidth (remember on TV we are listening to range of 6 MHz, not a single frequency) becomes less.

How much less depends on the type of noise and the distance. Lightning being a huge spark goes farther than the spark plug from a lawn mower. Simply because the electrical discharge from the lightning is greater than a spark plug.

So besides other factors that can influence impulse noise it follows three basic rules to determine its strength.

1) The amount of energy discharged in the spark
2) How far away your antenna is from the spark
3) The energy from the spark is roughly inversely proportional to the frequency of your antenna and receiver system. (the higher the frequency the less energy there is in the spark at that frequency).

I looked for detailed reports on the exact energy of lightning at given frequencies. Most of them are in books and only limited references available on line (yes there is a wealth of copyrighted knowledge not on the internet for free). Another interesting thing I found is most of the studies have been below 10 MHz, well below the TV frequencies.

But all of us know that have watched DTV for a number of years, lightning and impulse noise are still strong enough at even high band VHF to cause picture break up. Much worse at low band and not much at all at UHF.

Lets examine some implications of item 3 from above list, with the concepts below:

A) The higher the frequency the less energy lightning transmits to your antenna.

B) The TV band is not continuous. There are gaps between the three bands.

54 to 88 MHz Low Band - 34 MHz wide

With a 86 MHz Gap to
174 to 216 MHz High Band - 42 MHz wide

With a 254 MHz Gap to
470 to 698 MHz UHf Band - 228 MHz wide

Pay particular attention to the gaps between the bands. While the characteristics of the frequencies are not linear, they this shows an important relationship.

a) First look at the gap between low and high band VHF. It's more than the total space used by both low and high band! This means that high band will act a lot different than low band to a large extent.

b) Then look at the huge gap between high between high band and UHF. It's even more than the new UHF is wide! Its just short of 3 times difference between low and high band VHF. This means the characteristics of UHF are much different the VHF.

Remember too I am comparing the frequency difference in a strictly linear fashion, but impulse noise not only drops off as the inverse of the frequency but in a non linear fashion with it's exponent greater than negative one. I am not positive but I believe this reduction in noise as the frequency goes higher is better expressed as a depleting area under the curve than a simple inverse non-linear relationship (more than one inverse term). In common terms, it drops off faster and faster the frequency increases.

So there you go and hence lightning interference is just about none existent at UHF unless the strike if very close.

Asides:

1) If you start experiencing a lot of breakups on UHF there is good chance a thunder cell producing a tornado is very very close to your house.

2) Something I ran into that was interesting though I could only find one study on the subject. Cloud to cloud lighting has been seen to emit more energy at much higher frequencies than cloud to ground. If this is true, I speculate this is why on VHF it's possible to have interference from lighting from storms 100 miles away on low band and 60 miles plus on high band.

Consider the implications of this. Cloud to cloud lightning happens at altitude, the entire length of the strike. The energy is released from the equivalent of a tower that can be as high as 5K to 10K meters! A tower that high has some serious range! Additionally, most cloud to cloud lightning strikes are horizontal. Lightning puts off an electromagnetic wave which all have alternating electrical and magnetic fields, cloud to cloud a good deal of the electrical wave or emitting dipoles are horizontal, just like our TV antennas!

So not only is there some evidence that cloud to cloud lightning puts out more energy at higher frequencies than cloud to ground, but it's transmitted from an over all higher altitude with it's e-field horizontal, just like a TV receiving antenna.

It's not wonder we can be bothered on VHF by lightning so far away!