WJIB at night

[Eric Scott <Eric@wjyy.com>]

Last night (5/25) I was driving in West Peabody (MA) flipping through the AM 
band and caught WJIB at about 930pm. I thought WJIB had a blistering 5w of 
power...how can a signal carry that far at that power? It wasn't great, but it 
was listenable. This was a stock Delco radio in a Lumina-and the engine was 
running! Was this a fluke? I had it maybe 3 miles, and lost it on 128.
WCCM (800,Lawrence) was very listenable at their 203 watts, too-and it's 
usually not there at all. But, 5000 watt WUNR (1600,Brookline) was totally 
lost.
Can AM reception vary due to atmospherics?