Mzuzu sits higher than Lilongwe and feels it after sunset in the dry season. Days can be bright while nights need a sweater, especially in June, July, and August.
If you are travelling from the south, pack a light jacket even if the afternoon looks hot. Guesthouses in the north often have thinner blankets than you expect.
Rainy season mist on the M1 toward the north can cut visibility. Leave earlier if you are driving after a storm.