Decoding Lesson #1

Austin-Bergstrom International Airport (KAUS) is located in the capitol of Texas. Austin is typically a relatively dry place compared to most of the state to the south, yet conditions can be stormy, or as is the case today, foggy! Here's the current surface observation:

KAUS 221253Z 00000KT 1/4SM R17L/1200V1600FT FG OVC001 17/17 A3000

At 1253Z (7:53 AM CDT) winds were calm (00000KT) and visibility was a quarter of a mile (1/4SM). At this hour Austin is also reporting Runway Visual Range (RVR). The code follows the visibility token because RVR is calculated from visibility, ambient light level, and runway light intensity, and is the maximum distance at which the runway, or the runway lights can be seen.

In this case, the RVR is for Runway 17L, the only runway at Austin that has CAT II/III approaches. The 1200V1600FT part of the RVR token in this METAR indicates that the runway is visibile from between 1200 to 1600 feet (V=variable).

If you were wondering what was causing the poor visibility in the Lone Star State's capitol this morning, just refer to the next token: "FG" - it's the symbol used for fog. Also, the ceiling is reported overcast at 100 feet above ground level.

Finally, the temperature-dew point spread definitely indicates fog. Fog is probable when the temperature-dew point spread is 10°C (50°F) or less and decreasing. Fog usually forms when the dew point and the temperature are within a few degrees of each other, and will start to lift when the temperature-dew point spread begins to increase.

Finally, the surface pressure is reported at 30.00 inches of Mercury (A3000).

I'm listening to Austin Departure and they are reporting that the RVR is currently 6000 feet, so it sounds like conditions are improving - likely that temperature-dew point spread is helping out.