Take a look at the following surface observation from Charlotte (KCLT)... KCLT 251320Z 14010KT 10SM -RAPL OVC050 M04/M13 A3044 RMK AO2 RAB19PLB19 P0000 Notice anything wrong? Well, first of all, it's not an automated report...it's from Charlotte Douglas International airport (KCLT), the sixth busiest airport in the United States. An observation from a Class B primary airport such as KCLT should always be carefully scrutinized and augmented (as necessary) by a trained human observer. But, the precipitation type is -RA when the temperature is -4°C. Is it possible that it could be raining with a temperature of -4°C and not freezing on contact at the surface? Yes, but that would be highly exceptional. It's clear that it should have been augmented to -FZRAPL. No indication that the FZRA sensor is not operational. A bit later, the surface observation is reporting UP (unknown precipitation type). An augmented station such as KCLT should never report UP. There's a human observer at the airport and they should be able to observe what's going on. It's likely that ice pellets were falling (PL) and may have been mixed with FZRA. I suspect this report is being sent out without any augmentation. Quite a shame since we're paying for a human observer at this airport. KCLT 251552Z 17005KT 7SM UP OVC039 M03/M11 A3041 RMK AO2 UPB33 SLP304 P0001 T10331106 A freezing rain event is the worst time for something like this to occur. Always look at neighboring stations in order to catch these kinds of issues.
Most pilots are weatherwise, but some are otherwise™
Scott Dennstaedt, PhD
Weather Systems Engineer
CFI & former NWS meteorologist