Yes. Everything in the atmosphere reflects the signal back. It's simply varying degrees of signal to noise. They've had this technology for decades.
random video: https://www.youtube.com/watch?v=_7TWAJ_bnhM
Now keep in mind, technically they could focus after they fire if the duration is longer than transit time. In turn using the weapon's reflection as the corrective signal. And if it's a pulse weapon, they can always use a modified signal from previous pulses. In addition to the fact that plasma is frequently created by this class of weapon which significantly reduces scatter and reflection.
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