"Has anybody else noticed 'warning signs' of an impending flare of PMR?"
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YES! I had trigeminal neuralgia (TN) and that always got worse before a flare of PMR. I absolutely could not let TN get riled up. I could handle "random electrical zaps" to my face once in a while. When those electrical zaps would happen more often ... sheer panic would start to set in. The stress of TN is hard to describe. TN isn't called the "suicide disease" for no reason. I used to call TN my "inflammation alarm." There was no amount of prednisone that I wouldn't take in a sometimes futile attempt to get my inflammation levels back down.

"Trigeminal neuralgia (TN), also known as "suicide disease", is a chronic pain disorder that causes severe facial pain and can lead to mental anguish:"
https://arizonapain.com/trigeminal-neuralgia-suicide-disease/
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It was pathetic to have to anticipate impending doom that those electrical shocks would cause. There was no amount of Prednisone I would NOT take to make those electrical shocks stop. When they would happen in pairs and triplets, I knew it was just a matter of time until the full on electricity would start.

The sad thing was that I knew that prednisone helped but I got push-back from neurologists who said TN was NOT treated with Prednisone. I would counter and say the stuff they treated me with was making TN worse.

I the end ... there was some redeeming value when a neurosurgeon said that people with TN usually had a list of pain medications a mile long to treat TN. He was amazed that he didn't see any pain medications listed for me. I told him that I only took Prednisone because nothing else worked. I think I noticed one eyebrow go up on the face of the neurosurgeon when I said that.

After surgery for trigeminal neuralgia, the surgeon said prednisone was helping the inflammation and swelling in the area around my brain stem where the problem was. Fortunately surgery stopped TN from happening at all so Prednisone wasn't the best solution.

The problem was a vascular issue that was compressing my trigeminal nerve. Inflammation and swelling can cause a lot of pain depending on where it occurs.