There are a couple of common issues that can cause weak receive, and they've been covered above, but here's a recap:
1. Antenna - antennas tuned for a different band can provide poor reception. Your CB antenna is tuned for 27MHz, so it's not going to perform well. However, antennas can work well on multiple bands, so all is not lost. Your CB antenna is primarily resonate at 27MHz, although it may work well on others. The longer whip of the CB antenna should work well for VHF, however the loading coil in the base can create an issue.
2. Receiver sensitivity. PRC covered it well above. Sounds like the WX receiver in his radio is working very well (very sensitive), however keep in mind that as the CB radios go down the assembly line, it's up to a human to adjust these receivers to work optimally. Could be yours didn't get quite the attention that PRC's did.
3. Coax/mount issues. Doesn't sound like it's an issue. I think you reported that your CB was working very well.
4. Nearby strong signals. A strong signal close by on a nearby frequency can desensitize the receiver. Probably not the issue, but it's a possibility.
5. Location. You mentioned a carport. If you have a structure between you and the transmitter site at McQueen Ridge (just south of Umunuhm - the one with the old USAF radar station still on top) that could be part of your issue.
I'd suggest trying it in a different location. Move out in the open where you have a clear view to the north.
Sounds like you did all the basic testing I'd have suggested. Could be your CB just doesn't have a sensitive WX receiver in it.
Since you have the Yaesu, it should work well on the weather band. Trying programming the WX frequencies in there. From where I am and at work, I can often get the one from San Francisco. It's weak and scratchy, but it's there.