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Kirk Mellish's Weather Commentary

Posted: 8:06 a.m. Friday, June 13, 2014

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By Kirk Mellish

Summertime weather vocabulary, forecast lexicon:


Probability

A chance, or likelihood, that a certain event might happen

Slight Chance

In probability of precipitation statements, usually equivalent to a 10-20 percent chance.

Chance A National Weather Service precipitation descriptor for 30, 40, or 50 percent chance of measurable precipitation (0.01 inch). When the precipitation is convective in nature, the term scattered is used. See Precipitation Probability (PoP).

Likely

(abbrev. LKLY) In probability of precipitation statements, the equivalent of a 60 or 70 percent chance.

** Isolated can be up to 30% i.e. 10-30 percent

ThunderstormA local storm produced by a cumulonimbus cloud and accompanied by lightning and thunder and often a heavy downpour small hail and strong gusty wind. A thundershower is a lighter more tame version.


ThunderThe sound caused by rapidly expanding gases in a lightning discharge.

 

hail: pellets or balls of frozen rain that fall in showers from cumulonimbus clouds/thunderhead

Shower

A descriptor, SH, used to qualify precipitation characterized by the suddenness with which they start and stop, by the rapid changes of intensity, and usually by rapid changes in the appearance of the sky.

Severe Thunderstorm

A thunderstorm that produces a tornado, winds of at least 58 mph (50knots), and/or hail at least 1" in diameter. Structural wind damage mayimply the occurrence of a severe thunderstorm. A thunderstorm wind equalto or greater than 40 mph (35 knots) and/or hail of at least 1" isdefined as approaching severe.

CIN

Convective INhibition. A measure of the amount of energy needed in order to initiate convection. Values of CIN typically reflect the strength of the cap. They are obtained on a sounding by computing the area enclosed between the environmental temperature profile and the path of a rising air parcel, over the layer within which the latter is cooler than the former. (This area sometimes is called negative area.)

Shortwave  Also shortwave Trough: a disturbance in the mid or upper part of the atmosphere which induces upward motion ahead of it. If other conditions are favorable, the upward motion can contribute to thunderstorm development ahead of a shortwave. 


MOS Model Output Statistics - the Hydrometeorological Center (HPC) produces a short range (6 to 60 hours) MOS guidance package generated from the NGM, GFS, and ETA models for over 300 individual stations in the continental United States. These alphanumeric messages are made available at approximately 0400 and 1600 UTC for the 0000 and 1200 UTC forecast cycles, respectively. Model Output Statistics are a set of statistical equations that use model output to forecast the probability of precipitation, high and low temperature, cloud cover, and precipitation amount for many cities across the USA. The statistical equations were specifically tailored for each location, taking into account factors such as each location's climate.


Synoptic Scale The spatial scale of the migratory high and low pressure systems of the lower troposphere, with wavelengths of 1000 to 2500 km.


Mesoscale Size scale referring to weather systems smaller than synoptic-scale systems but larger than storm-scale systems. Horizontal dimensions generally range from around 50 miles to several hundred miles. Squall lines, MCCs, and MCSs are examples of mesoscale weather systems


Microscale Pertaining to meteorological phenomena, such as wind circulations or cloud patterns, that are less than 2 km in horizontal extent.


Numerical Weather Prediction Same as Numerical Forecasting; a computer forecast or prediction based on equations governing the motions and the forces affecting motion of fluids and gases. The equations are based, or initialized, on specified weather or climate conditions at a certain place and time, fluid dynamics, thermodynamics, kinematics and other laws of physics and differential equations advanced algebra/calculus are the basis for meteorology and weather forecasting.

(NWP) involves constructing a three-dimensional grid of the atmosphere using data on the atmosphere’s current state, and using a mathematical model to predict its evolution into future states. Taking readings on the temperature, humidity, barometric pressure, wind speed and direction, and precipitation for each point on that grid, and repeating that process every 10 minutes or so, provides a stream of data that feeds into mathematical algorithms that seek to predict future states. These algorithms’s success is later analyzed, and revised to improve predictive quality over time.

See 
http://www.scn.org/~bm733/infaq.html 
Also http://www.scn.org/~bm733/wx_gloss.html />

Kirk Mellish

About Kirk Mellish

Kirk Mellish is Atlanta's first and only full-time radio meteorologist. He's also the FIRST broadcast meteorologist in Georgia and the Southeast to earn the American Meteorological Society's new Certified Broadcast Meteorologist (CBM) designation.

Send Kirk Mellish an email.

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