JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
MILLIBAR – (Bar – a unit of pressure equal to 1,000,000 dynes per square centimeter.) A
millibar is equal to 1/1000 of a bar.
MIST – A hydrometer consisting of an aggregate of microscopic and more-or-less hygroscopic
water droplets or ice crystals suspended in the atmosphere that reduces visibility to less than 6
statute miles but greater than or equal to ⅝ statute mile.
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 6 feet above the
ground and apparent visibility in the fog is less than ⅝ SM. Visibility over parts of the station is
less than or equal to ⅝ 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 6 feet above
the ground and the apparent visibility in the fog patch or bank is less than ⅝ SM. Visibility in
parts of the observing area is greater than or equal to ⅝ SM, when the fog is close to the point of
observation, the minimum visibility reported will be less than ⅝SM.
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.
RADIOSONDE – A balloon-borne instrument used to measure the temperature, pressure and
humidity aloft.
Version 3.2/Dec 08 A-5