In Central Region Technical Attachment 87-23 (October, 1987), George Maglaras reviewed the MOS Probability of Snow Amount (PoSA) system and presented some guidelines for its use. I recently completed a case study that confirmed these guidelines and led to some additional conclusions. Here, I've reviewed the PoSA systan (in case George's paper is not available to you) and provided an updated list of operational guidelines that you can refer to when time is short and the flakes start flying.

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