Would you give someone a better tip for delivering your food in a blizzard?

Food orders increase when bad weather hits -- as do tips, according to online food delivery company GrubHub. But severe winter weather can push tips up even higher.

This year, tips in New York City increased 9% during the Jan. 26 snow storm compared to the city's year-round average. In Boston, tips rose 6% during the Feb. 2 blizzard and gratuity jumped 12% in Chicago during the Feb. 1 storm.

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Even extreme cold is enough to make some customers more generous.

"If the temperature drops significantly, or there's something out of the ordinary, we see a high correlation with tip percentages and temperatures," said Allie Mack, a spokeswoman for GrubHub.

For example, during the 2013-2014 winter season, the company said the average tip was 14.1%, only a slight increase from the 13.9% average over the rest of the year. But during the Polar Vortex in January 2014, average tips jumped in some colder cities. Tips were more than 15% higher than average in Detroit and Minneapolis on certain days of the month.

The tips are analyzed as a percentage of the overall order, and cash tips can't be tracked. At the end of ordering process, GrubHub customers can select to add a 10%, 15% or 20% tip or add their own amount.

For the entire 2013-2014 winter, the highest tipping cities were: Denver at 15.7% of the total delivery price, Dallas at 15.1% and Charlottesville, Virginia, at 15%.

Early deliveries also tend to get higher tips. Tipping percentages increased 7.3% from the daily average from 6-9 in the morning in the winter season. "Perhaps people are being more generous because they aren't ordering as much," Mack said.