I think a Biblical storm would need to:
1) Be unequivocally a storm of record. Call it a Mt. Rushmore storm or whatever based on your climo.
2) Have a generational to unprecedented to level of impact. You have to adjust for societal & technological changes to a degree, but biblical impacts are still possible in storms.
The Buffalo Christmas event while not an EC storm is a good example of something “biblical”. Unprecedented snowfall and wind combination in the historical record combined with catastrophic societal impacts. People literally freezing to death across the metropolitan area. Insane in any time period.
It’s part of the reason why I’d call October 2011 a BECS level event in CT too. Unprecedented snowfall (for time of year) combined with catastrophic societal impacts through power grid failure.