I don't think fireworks are the problem, and clouds are part of weather conditions, which CAN vary reception
If you are using the scanner on a base installation, put up a good outside scanner antenna, and find out what
stronger signals do to the front end of the scanner. I've been on scanners since they were invented in the 60's,
and build a lot of my own antennas. I built a multi-band (150/440/850 mHz) parallel dipole into an enclosed
PVC pipe, ran that in a sideways T design, with a bottom downward PVC leg for mounting to a mast or bldg.
I used 75 ohm TV connectors, and an adapter from F connector to mini TNC connection on the scanner.
I ran that on one scanner and then on the HP for 15 years before water finally permeated it.
Barring all that, find an old TV beam antenna, remount it vertical instead of horizontal, and use 75 ohm cable
and connectors (F). You'll be surprised at what you get. If you put the antenna on a TV rotor, then you'll be
able to select the direction for best signal, and your HP will thank you for it...unless you overload the front end
with too strong locals!! Just an advisory. DUKE, WB9OJD