There are some tracks MotoGP goes to where you can pretty sure of what to expect. Jerez will be sunny and warm, though some years are warmer than others. Motegi will be cold, with a good chance of rain. The heat in Thailand and Sepang will be brutal, with a 4pm downpour in Sepang pretty much guaranteed.
There are other tracks where you are pretty much guaranteed a bit of everything. Sachsenring will invariably have one cold morning and one wet morning, and a sweltering afternoon. The wind at Assen means there is a good chance of rain showers in any given session, but also a good chance they have swept over the circuit and the track has dried out before the session is over. And crowning it all is Phillip Island, where it's not so much four seasons in one day, as four seasons in one 15-minute qualifying session. Given the full 45 minutes of FP2, there's a good chance of seeing a dozen or more seasons, including a couple you have probably never heard of.
Le Mans is a circuit in a similar mold. Packing for Le Mans invariably means taking a larger suitcase, as you will need something warm enough for the chill of a May morning, along with something light enough to handle the chance of a warmth Spring afternoon. And you will definitely need your waterproofs. And possibly a second set, for once the first set gets drenched through.