Sometimes weather reports include codes that you've never seen before. Here are 9 codes that may leave even the most seasoned aviator stumped.

1) PRESFR

This code stands for pressure falling rapidly or, on the other hand, PRESRR, for pressure rising rapidly. These may be included in METARs that include convective activity. Pressure falling rapidly is usually indicative of a weather event associated with a low-pressure system that is approaching quickly.

2) 6////

According to the Federal Meteorological Handbook No.1, when METARs include reports on accumulated rainfall over a 3-6 hour observation, you may see this code. It means that there is an indeterminable amount of precipitation that has fallen during this time. If you are landing at an airport that may have had significant rainfall or other precipitation, you may want to be careful of hydroplaning hazards, especially with a report that isn't able to give you the information you need.

3) RVRNO

This code stands for "RVR Not Available." When RVR values are necessary to be reported but aren't available due to an issue with the RVR system, you will see this code in the METAR.

4) PK WND

This code stands for peak wind. You may find this code when conditions at the airport are gusting consistently or have had strong sustained winds over the course of the observation period. A "PK WND" value will indicate the wind direction, velocity, and time after the hour that it was observed.

5) FROPA

According to the Federal Meteorological Handbook No.1, this code follows a wind shift observation that is associated with a frontal passage.

6) WSHFT

This code stands for a wind shift and will be included in a report when winds shift rapidly throughout the observation period. This is usually due to changing air masses associated with weather/frontal systems.

7) NOSPECI

Certain airports are fortunate enough to give out special reports when the weather at the field changes rapidly and triggers the "SPECI" criteria. However, in the event you are at an airport where special reports are unavailable, "NOSPECI" will be the code you see in the remarks section of the METAR.

8) CBMAM

When significant weather is in the vicinity of the observation station, the associated cloud types and their direction of travel will be indicated. In this code, "CB" stands for cumulonimbus and "MAM" stands for Mammatus.

9) CC, CA or CG

These codes, which stand for cloud to cloud, cloud to air, and cloud to ground, respectively, are types of lightning reports that you will find associated with hazardous weather systems in the vicinity of the observation station.

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