a temperature scale on which the boiling point of water is at 212 degrees above the zero of the scale and the freezing point of water is at 32 degrees above zero
same as Virga. Streaks or wisps of precipitation falling from a cloud but evaporating before reaching the ground. In certain cases, shafts of virga may precede a microburst.
the region of the electromagnetic spectrum with wavelengths greater than infrared but shorter than microwaves; radiation between about 4 microns and 0.1 millimeters
a Department of Transportation agency that regulates and oversees all aspects of civil aviation in the U.S.
lines or bands of low-level clouds that move (feed) into the updraft region of a thunderstorm, usually from the east through south (i.e., parallel to the inflow). Also known as inflow bands. In tropical meteorology, this term describes spiral-shaped bands of convection surrounding, and moving toward, the center of a tropical cyclone.
in the general circulation of the atmosphere, the name given to the middle latitude cell marked by sinking motion near 30 degrees and rising motion near 60 degrees latitude
the law of physics that states that the heat absorbed by a system either raises the internal energy of the system or does work on the environment
a line of cumulus or towering cumulus clouds connected to and extending outward from the most active part of a supercell, normally on the southwest side. The line normally has a stair-step appearance, with the tallest clouds closest to the main storm.
a local flood of great volume and short duration generally resulting from heavy rainfall in the immediate vicinity
the condition that occurs when water rises and overflows the natural or artificial confines of a body of water onto normally dry land, or accumulates in low-lying areas
a warm, dry wind on the lee side of a mountain range. The warmth and dryness of the air is due to adiabatic compression as the air descends the mountain slopes. A Chinook is the name for Foehn winds in the Rocky and Sierra mountains.
a specific area over which the conditions stated in a weather forecast are valid.
computer-generated forecast materials used to assist the preparation of a forecast
the main region of downdraft in the forward, or leading, part of a supercell, where most of the heavy precipitation occurs
(0=driest, 1=wettest) as soil moisture increases (soil gets wetter), the FWI increases as well. For completely saturated soil (can’t hold any more water) the FWI is close to 1.0. A powder-dry soil has an FWI near zero. The Oklahoma Mesonet soil moisture is shown as an FWI.
the part of the atmosphere that lies above the frictional influence of the earth’s surface.
a condition that occurs over a widespread area when the surface air temperature remains below freezing (below 32°F) long enough to damage agricultural crops
drizzle that falls as liquid water but freezes upon impact to form a coating of ice upon the ground and on exposed objects
liquid precipitation that freezes upon impact with the ground or exposed objects (freezing rain or freezing drizzle).
rain that falls as liquid water but freezes upon impact to form a coating of ice upon the ground and on exposed objects
the rate at which an event will reoccur; the reciprocal of the period. In radiation, the number of wave crests that pass by a point each second, described in hertz.
the mechanical resistive force of one object on another object’s relative movement when in contact with the first object
a temperature inversion in the atmosphere resulting from the vertical boundary between two air masses along a sloping front
the movement of a front across an area; characterized by changes in temperature, pressure, wind direction and speed, visibility, cloudiness and precipitation
a transition zone between air masses with different temperature and moisture characteristics.
the process of front formation. This occurs when there is an increase in the temperature gradient across a front.
the process of front dissipation. This occurs when the temperatures and pressures equalize across a front.
the formation of ice crystals on the ground or other surfaces under conditions similar to dew, except the temperature and dew point of the Earth’s surface and earthbound objects fall below 36°F.
when liquid dew changes into tiny beads of ice. This occurs when dew forms and temperatures later drop below freezing.
precipitation that reaches the ground in frozen form. Examples include snow, snow pellets, snow grains, ice crystals, ice pellets (sleet), and hail.
the scale used to classify the strength of a tornado. It was devised by Dr. Theodore Fujita from the University of Chicago and was originally created to smoothly connect the Beaufort and Mach Scales. It has been replaced by the Enhanced Fujita Scale (EF Scale) on February 1, 2007. Tornadoes before this date retain their F Scale value and have not been converted to the EF Scale. All tornadoes after February 2007 are assigned an EF Scale value.
F0 |
Weak |
40 - 72 mph |
Light damage |
F1 |
Weak |
73 - 112 mph |
Moderate damage |
F2 |
Strong |
113 - 157 mph |
Considerable damage |
F3 |
Strong |
158 - 206 mph |
Severe damage |
F4 |
Violent |
207 - 260 mph |
Devastating damage |
F5 |
Violent |
261 - 318 mph |
Incredible damage |
when two rotating systems (e.g., lows or tropical cyclones) rotate around each other. It is similar to a spinning teacups ride--each teacup spins independently, while all of the teacups move in a large circle
a rotating cloud column or inverted cloud cone extending downward from a cloud base that is not in contact with the ground