Seasoned beekeepers learn to pay attention to the activity of the bees as it relates directly to the weather.
Most evenings around 5:00PM the bees are still quite active, mostly coming in from a long day of foraging (or finishing up orienting flights). Last evening I checked the bees, and there were very few bees still out. Most had gone in already. And this morning, the bees weren't really coming out and starting their collecting activities like they had in days past.
Sure enough, the weather forecast is for some rain later today, and even I can tell it in the air. You also don't want to work the bees when the weather is bad - they get cranky!
Last night I filled up the jar with sugar syrup - the bees had consumed the syrup that was there. I just gave them a little smoke to do it - I didn't suit up or anything. The jar is just under the outer cover, so I don't have to disturb too many bees (just the dozen or so who were on the feeder and who came out to investigate what I was doing). I'll be feeding them right up until winter, in order to get them built up strong enough to survive the winter (that hive was started late in the season).
Speaking of eating, the bees also need water. I think my bees get theirs from my next door neighbor's Koi pond. I had put out a bucket for them early on, and they ignored it (bees prefer running water to standing water).
One of the 50 or so bee blogs I follow posted this picture of his bees drinking. I thought it was so cute!!
(picture is from this blog post)