High humidity and heat are a nasty combination because the body can not cool down properly, so maybe it makes things harder for MS patients as well.

When the total sum of temperature plus the humidy percentage exceeds
150, many sporting events are cancelled because the risk of severe dehydration and heat stroke is so much higher than when that sum total is below 150.
For example if the temp is 90F and the humidiy is 60%, that equals 150 and the chance of heat stroke is higher.

It would be interesting to know how if that total number affects MS in a similar fashion. Maybe we should all keep track of it for a bit?