storage of BL21 at -20 - (Sep/25/2013 )

Hi I 

Due to logistical problems I wish to store my E. Coli BL21 at -20C instead of -80 for a period of 4 months.

Am I likely to experience a drop in viability, or would it be OK?

Best 

For glycerol stocks, yes, there will be a big drop off in viability.  -20 does not work for storage of glycerol stocks as they do not freeze.