The Forum of Private Business (FPB) has made the warning with forecasters predicting an end to the unseasonably mild conditions across the UK towards the end of November.
The Forum says SMEs can be particularly vulnerable to the impact of freak weather and should start planning ahead by checking their premises are winter-proof, insurance is up to date, and contingency plans are well-thought-out in case staff can't get in to work.
The past two winters have seen Arctic weather cause havoc for British businesses due to the disruption, and, according to early long range forecasts, December is likely to start with severe frosts with the chance of snow for many areas closer to Christmas.
According to data from YouGov's Omnibus SME survey, 13% of small businesses said they were 'seriously' impacted by last winter's bad weather, and 37% said they experienced weather-related problems of some sort.
YouGov figures also showed during winter 2010 that 34% of workers experienced 'significant problems' getting to work, with 10% unable to get in at all at some point. 8% of workers were prevented from going in to work at least once because their children's school had closed due to the bad weather - significantly more women than men cited this as a reason for absence.
In the wake of the summer riots, and more recent flash flooding which affected parts of the south, the Forum is also highlighting the need for firms to regularly review basic disaster recovery plans in general.
While small businesses will usually get an insurance payout to cover damage to their property after freak events, they are highly vulnerable to the steep drop in turnover, which often follows as customer records are lost, phone calls and emails go unanswered and clients take their custom elsewhere.
The FPB's head of campaigns Jane Bennett said: "Disruptive snowfall hampers deliveries, triggers heating and power failures, and can sometimes mean employees can't get to work.
"The past few winters have demonstrated just how susceptible the UK is to extreme weather, and the cost to business quickly runs into millions. When infrastructure grinds to a halt staff can't get in to work, and that's a body blow which hits small firms with fewer staff the hardest.
"It's essential small businesses do all they can themselves to mitigate the impact, and being proactive now will mean not having to rush out a last minute reactive plan on the eve of bad weather, which may not be all that effective.
"It worth remembering prevention is also better than cure - something as simple as making sure water pipes are lagged could save a business thousands in lost revenue if it has to close because of flooding. Businesses need to think about their contingency plans now to ensure they aren't put out of action by another nasty winter.
"A high percentage of businesses affected by a major incident such as a flood or a fire either never re-open or go bust soon after the event.
"This is often not due to the immediate loss of goods and premises, which is usually covered by insurance payouts. It's because the company's inability to resume trading within a short space of time means clients and customers go elsewhere, leading to unsustainable losses and potentially undoing years of hard work spent building the business up."