Z

Zulu time; the same as Universal Coordinated Time (UTC), i.e. 18z is the same as 18:00 UTC.

Zero Datum

In hydrologic terms, a reference "zero" elevation for a stream or river gage. This "zero" can be referenced (usually within ten feet of the bottom of the channel) to mean sea level, or to any other recognized datum.

ZFP

Zone Forecast Product

ZL

Freezing Drizzle

ZNS

zones

Zonal Flow

Large-scale atmospheric flow in which the east-west component (i.e., latitudinal) is dominant. The accompanying meridional (north-south) component often is weaker than normal. Compare with meridional flow.

Zone of Aeration

In hydrologic terms, the locus of points just above the water table where soil pores may either contain air or water. This is also called the vadose zone

Zone of Saturation

In hydrologic terms, the locus of points below the water table where soil pores are filled with water. This is also called the phreatic zone

Zoned Embankment Dam

In hydrologic terms, an embankment dam which is comprised of zones of selected materials having different degrees of porosity, permeability and density.

ZR

Freezing Rain

Zulu (Z) Time

For practical purposes, the same as Coordinated Universal Time (UTC). The notation formerly used to identify time Greenwich MeanTime. The word "Zulu" is notation in the phonetic alphabet corresponding to the letter "Z" assigned to the time zone on the Greenwich Prime Meridian.

Zurich Sunspot Classification

In solar-terrestrial terms, a sunspot classification system that has been modified for SESC use.

Z\/R Relationship

An empirical relationship between radar reflectivity factor z (in mm^6 / m^3 ) and rain rate ( in mm / hr ), usually expressed as Z = A R^b; A and b are empirical constants.