aerial tv signal ampliication?

A reasonably modern TV will have a good input circuit, probably as good as a booster amplifier. Thus putting a booster amplifier in front of the set will help very little if at all.
A booster amplifier at the aerial however is beneficial. The signal is attenuated in the down cable and boosting to compensate for this loss can help a lot, depending on the cable length and loss/metre. 18dB boost should be plenty.

Weather can affect the signal. If there is high pressure and a temperature inversion, signals can come in from an enormous distance and interfere with the wanted signal. A more directional aerial may help in this case. Rain and snow can absorb UHF signals.

 

TV signal

In our house ive put an Arial in the loft, a hi gain type lots of elements, its coupled to a UHF amp to give me a said 40 db gain or so, our country here in the UK has just had the digital switch over from analogue to digital signal, i would check all your coax plugs and joins if any, i don't think adding another amp down line will do either unit much good, if coax and plugs are all ok, go for an amp with a bit more gain, has the Ariel connections been done properly, our units connection box on the antenna does not give much room between braid and core connections, they must not come into contact with each other, or your reception will be terrible. Dave. PS if i remove our amplifier and couple up with a female both ends joiner are signal deteriorates considerably to being unwatchable.