Twice a year, I feel compelled to talk about Daylight Saving Time and how it negatively affects timely access to updated evening weather model data before bedtime for those of us on the east coast.

Frankly, I love Daylight Saving Time and the extra hour of daylight we get in the late afternoon. The problem for us weather people is that major weather models are run worldwide at “00z” (Coordinated Universal Time or what used to be called Greenwich Mean Time). This corresponds to 7 PM Eastern Standard Time, but 8 PM Eastern Daylight Time. That hour makes a difference.

Since numerical weather models take 2-5 hours to ingest data, compute and process, many of the major models become available too late in the night to be any use for us on the East Coast for planning our activities the following day.

When you hear “tune back in at 11″, you’re not going to see any change in the 5 day forecast at 11PM and likely to see little change in the next day forecast; new model data simply hasn’t become available yet.

So for us weather people, the return to Eastern Standard Time makes a big difference for last minute evening updates about snow storms.

Here’s some of the changes in some model availability (eastern time) :

I’ve written extensively about Daylight Saving Time in past years—

Little Known Facts about Daylight Saving Time and TV Weather Forecasts

Daylight Saving Time and Weather Models

“Check Back at 11” — TV Weather and Daylight Saving Time