Originally Posted by
CurtainTwitcher
I look at the METAR last 10 minute rainfall and rainfall since 0900 to give me a ballpark idea of the rain system. if you use 4.0mm per hour as the upper limit of moderate, just divide that by 6 (6 ten minute period per hour) is 0.7mm, If I am going somewhere short and ungrooved/non-PFC, I plug in RCAM Runway Condition Code 2 in the OPT.
If it is grooved/PFC I uses 7.6mm per hour, this equates to 1.2mm in the last 10 minutes before I plug in code 2. I then assess LDA vs required. If I can't do it, I hold then divert. I have diverted from a very short runway in the Whitsunday's (despite the CAVOK forecast, subsequent METAR showed 15mm of rainfall had occurred during the hour that covered our arrival period, tower reported visibility was between 900 and 1900m vis). At non-tower ports, you use the AWIS last 10 minute figure that is literally updated instantaneously, and is more useful that the slightly stale METAR.
Thanks for sharing - very useful.