Kevin,

FYI, Maximum Usable Frequency normally refers to HF propagation.  The Band
openings on VHF have other influences.

One which can affect 6 and 2 meters, is scattered E ionization.  This does
relate to MUF, as there needs to be a lot of ionization to reach the lower E
layer.  At times, there will be a track of ionization which will bend signals
back to earth which would normally be line-of-sight.  I've seen communication
between Florida and here in Michigan on 146MHz based on scattered E.
Typically, one would expect scattered E incidents around this time of year.

The other phenomenon which afects VHF and UHF particularly at 144MHz and
higher, is tropospheric communication.  Often, troughs are formed between
warmer layers of air near the earth and cooler ones above, or between the
boundaries of cold and warm fronts.  I've seen fairly long paths using tropo
here in Michigan extending more often than not on a more east-west path or
northeast-southwest.  In general, I've seen more north-south paths using
scattered E.

Steve, K8SP