SEVERE WEATHER ALERTS DEFINED:
Tornado WATCH: A tornado watch means that conditions are favorable for the development of severe weather including tornadoes. It does not mean a tornado is imminent or occurring, but that you should monitor the weather conditions closely and listen for updates. A watch is not always issued prior to a warning.
Tornado WARNING: A tornado warning means a tornado is imminent or occurring and that you need to seek shelter immediately. A tornado has either been sighted or strong rotation has been detected on radar and a tornado may form at any moment.
Severe thunderstorm WATCH: A severe thunderstorm watch means that conditions are favorable for storms to produce damaging winds and large hail. Like with a tornado watch, it doesn't mean severe weather is imminent, but that you should closely monitor weather conditions and listen for updates. A watch is not always issued prior to a warning.
Severe thunderstorm WARNING: A severe thunderstorm warning means that a severe thunderstorm has been sighted or indicated on radar. A severe storm is defined as producing winds greater than 58mph, hail of at least 1" in diameter, or a tornado. Lightning/thunder and heavy rain have nothing to do with the definition of a severe storm.
Tornado WARNING: A tornado warning means a tornado is imminent or occurring and that you need to seek shelter immediately. A tornado has either been sighted or strong rotation has been detected on radar and a tornado may form at any moment.
Severe thunderstorm WATCH: A severe thunderstorm watch means that conditions are favorable for storms to produce damaging winds and large hail. Like with a tornado watch, it doesn't mean severe weather is imminent, but that you should closely monitor weather conditions and listen for updates. A watch is not always issued prior to a warning.
Severe thunderstorm WARNING: A severe thunderstorm warning means that a severe thunderstorm has been sighted or indicated on radar. A severe storm is defined as producing winds greater than 58mph, hail of at least 1" in diameter, or a tornado. Lightning/thunder and heavy rain have nothing to do with the definition of a severe storm.
WEATHER TERMS WE USE DEFINED:
CAPE: This stands for Convective Available Potential Energy, which is a way to measure how unstable the atmosphere is. The higher the CAPE, the more unstable the air is. In our area, unstable air usually has about 1,000 j/kg of CAPE, and anything over 1,500 j/kg of cape is considered moderate to strongly unstable. The more unstable we are, the stronger storms have the potential to be. CAPE is highest on hot and humid days in the summer time.
WIND SHEAR: This is the change of wind direction and/or speed with vertical height within the atmosphere. Wind shear is critical in tornado formation. Wind shear on a given severe weather day can range from 30kts to 60kts, with 40+kts very favorable for tornado development. Wind shear is measured in the lowest 1km, 3km, and 6km of the atmosphere.
SRH: Storm Relative Helicity (SRH) is a form of wind shear used specifically for tornado forecasting. This is the change in wind speed and direction with height in relation to storm motion. When other severe weather ingredients are in place, 150 m2/s2 of SRH is considered favorable for tornado development.
LAPSE RATES: Lapse rates are the change in temperature as you go up in the atmosphere. The quicker the temperature decreases, the steeper the lapse rates and the more unstable the atmosphere will be.
COLD AIR ADVECTION: Simply put, it is the advection or movement of cold air into a region. This usually occurs with a North or Northwest wind after the passage of a cold front.
WARM AIR ADVECTION: Simply put this is the advection or movement of warm air into a region. It usually occurs on a south wind following the passage of a warm front.
INVERSION: Sometimes, a shallow layer of warm air develops just above the surface, leading to a cap over the atmosphere. This basically puts a lid in the lower atmosphere which prevents the stronger winds rom mixing down and make thunder much louder as it traps the sound.
LLJ: These are the winds at about 5,000 feet or 850mb above the surface. During severe weather events, these winds can reach speeds of 80mph and be translated down to the surface in the form of damaging downburst winds.
WIND SHEAR: This is the change of wind direction and/or speed with vertical height within the atmosphere. Wind shear is critical in tornado formation. Wind shear on a given severe weather day can range from 30kts to 60kts, with 40+kts very favorable for tornado development. Wind shear is measured in the lowest 1km, 3km, and 6km of the atmosphere.
SRH: Storm Relative Helicity (SRH) is a form of wind shear used specifically for tornado forecasting. This is the change in wind speed and direction with height in relation to storm motion. When other severe weather ingredients are in place, 150 m2/s2 of SRH is considered favorable for tornado development.
LAPSE RATES: Lapse rates are the change in temperature as you go up in the atmosphere. The quicker the temperature decreases, the steeper the lapse rates and the more unstable the atmosphere will be.
COLD AIR ADVECTION: Simply put, it is the advection or movement of cold air into a region. This usually occurs with a North or Northwest wind after the passage of a cold front.
WARM AIR ADVECTION: Simply put this is the advection or movement of warm air into a region. It usually occurs on a south wind following the passage of a warm front.
INVERSION: Sometimes, a shallow layer of warm air develops just above the surface, leading to a cap over the atmosphere. This basically puts a lid in the lower atmosphere which prevents the stronger winds rom mixing down and make thunder much louder as it traps the sound.
LLJ: These are the winds at about 5,000 feet or 850mb above the surface. During severe weather events, these winds can reach speeds of 80mph and be translated down to the surface in the form of damaging downburst winds.