A layer of relatively warm air aloft, usually several thousand feet above the ground, which suppresses or delays the development of thunderstorms. Air parcels rising into this layer become cooler than the surrounding air, which inhibits their ability to rise further and produce thunderstorms. Sometimes called the lid.

Convective Outlook

A forecast containing the area(s) of expected thunderstorm occurrence and expected severity over the contiguous United States, issued several times daily by the SPC. The terms marginal, slight risk, enhanced risk, moderate risk, and high risk are used to describe severe thunderstorm potential. Local versions sometimes are prepared by local NWS offices.

By | January 15th, 2016|, |0 Comments


Tending to move toward one point or to approach each other. Convergence in a horizontal wind field indicates that more air is entering a given area than is leaving at that level.  Convergence at low levels may result in upward forcing; at higher levels convergence may result in downward forcing.  When other factors such as [...]

By | January 27th, 2016|, |0 Comments

Jet Stream

Along narrow meandering current of high-speed, high-altitude winds near the tropopause blowing from a generally westerly direction and often exceeding a speed of 250 miles (402 kilometers) per hour.  The position and orientation of jet streams vary from day to day. General weather patterns  are related closely to the position, strength and orientation of the [...]

By | January 27th, 2016|, |0 Comments

Mesoscale Discussion

When conditions actually begin to shape up for severe weather, SPC (Storm Prediction Center) often issues a Mesoscale Discussion (MCD) statement anywhere from roughly half an hour to several hours before issuing a weather watch. SPC also puts out MCDs for hazardous winter weather events on the mesoscale, such as locally heavy snow, blizzards and [...]