be snowed under
被 (雪 / 繁重的工作) 覆蓋；壓得喘不過氣

explanation :  This idiom doesn't necessarily have to do with winter. To be 'snowed under' means to be overwhelmed by a huge number of duties or jobs. 

e.g.  Mr. Martins is completely snowed under with all the requests that came in from new customers, and he won't be able to get to your account until next week.