Appendix A: Glossary -Cont.

APPENDIX A

METEOROLOGY FLIGHT PLANNING

MOIST ADIABATIC LAPSE RATE See Saturated Adiabatic Lapse Rate.

NON-UNIFORM SKY CONDITION A localized sky condition which varies from that

reported in the body of the report.

NON-UNIFORM VISIBILITY A localized visibility which varies from that reported in the

body of the report.

OBSCURED SKY The condition when the entire sky is hidden by a surface-based obscuration.

OBSCURATION Any aggregate of particles in contact with the earth's surface that is dense

enough to be detected from the surface of the earth. Also, any phenomenon in the atmosphere,

other than precipitation, that reduces the horizontal visibility.

OVERCAST A layer of clouds whose summation amount of sky cover is 8/8.

PARTIAL A descriptor, PR, used only to report fog that covers part of the airport.

PARTIAL FOG Fog covering part of the station and which extends to at least six feet above the

ground and apparent visibility in the fog is less than 5/8 SM. Visibility over parts of the station

is less than or equal to 5/8 SM.

PARTIAL OBSCURATION The portion of the sky cover (including higher clouds, the moon,

or stars) hidden by weather phenomena in contact with the surface.

PATCHES A descriptor, BC, used only to report fog that occurs in patches at the airport.

PATCHES (OF) FOG Fog covering part of the station which extends to at least six feet above

the ground and the apparent visibility in the fog patch or bank is less than 5/8 SM. Visibility in

parts of the observing area is greater than or equal to 5/8 SM, when the fog is close to the point

of observation, the minimum visibility reported will be less than 5/8 SM.

PEAK WIND SPEED The maximum instantaneous wind speed since the last METAR that

exceeded 25 knots.

PRECIPITATION DISCRIMINATOR A sensor, or array of sensors, that differentiates between

different types of precipitation (liquid, freezing, frozen).

PRESSURE FALLING RAPIDLY A decrease in station pressure at a rate of 0.06 inch of

mercury or more per hour which totals 0.02 inch or more.

PRESSURE RISING RAPIDLY An increase in station pressure at a rate of 0.06 inch of

mercury or more per hour which totals 0.02 inch or more.

A-6 GLOSSARY