Storm Prediction Center
The Storm Prediction Center (Centre for storm predictions) of the United States in Norman (Oklahoma) is one of the National Centers for Environmental Prediction. It is under the control of the National Weather Service, a division of the National Oceanic and Atmospheric Administration U.S. Department of Commerce. By October 1995, the Storm Prediction Center in Kansas City (Missouri ) was established under the name of National Severe Storms Forecast Center.
The Storm Prediction Center is responsible for the identification, description and assessment of risks posed by convective storms. These risks primarily include tornadoes, hail larger than 2 cm in diameter and winds with speeds of at least 93 km / h Also the tasks of the Storm Prediction Center, part of the warning of fire-prone areas, or heavy snow. The tasks are mainly followed by convective outlooks, severe thunderstorm watches and tornado watches, weather watches and mesoscale discussions. In a three-stage process, the area, the time and the details of a weather warning will always be more concrete, increasing the attention.
Convective outlooks
The Storm Prediction Center to make predictions on the general threat of konektive storms in the territory of the United States for the next 6-73 hours and divides the risks into three categories. There is a separate prediction for each of the coming days, which is updated up to five times daily.
Categories
The categories are ordinary storm (only short description), " SEE TEXT" ( an area on the map scattered storms or storm -like conditions ), " SLGT " ( low risks ), " MDT " (moderate hazard ), and "HIGH " ( great danger ).
Vulnerable areas ( in shaded representation on the map ) indicate a threat to a great extent. These include tornadoes from the strength F2, hailstones with a diameter of at least 5 cm or storms with speed exceeding 120 km / h Public weather warnings are issued when calculating with strong or widespread severe weather, especially in the case of tornadoes.
A day with low risks ( SLGT ) indicates occasional dangers of high winds, heavy hail or local tornadoes. During the storm season made on most days low risks to the individual areas of the USA.
Days with moderate hazards ( MDT) warn of more widespread and more dangerous storms. These can include numerous tornadoes with higher wind speeds, more widespread areas with strong winds and hail are looking with very large hailstones. On some days with moderate hazards, there is strong tornadoes or Derechos. Such warnings are not unusual and will be issued in the season several times a month.
A day with great dangers (HIGH) poses a significant probability of the occurrence of a large tornado or an exceptional Derechos. On such days, there is the risk of extreme storm with life-threatening effects of widespread severe or very severe tornadoes and / or other destructive winds. Hail alone can not trigger the highest warning level. Many of the days with the greatest destruction was predicted with such great dangers. This, there is usually only a few times each year.
It is important to note that these are only for use with categories to make predictions that do not always apply. So it was in the past to stronger tornadoes on days with low risks and a missed major risks are not uncommon.
The predictions
The prediction for a day is updated five times daily. At 06:00 UTC the first prediction is carried out for the period from 12:00 UTC to 12:00 UTC of the current day of the following day. Updates take place at 13:00 UTC, 16:30 UTC, 20:00 UTC to 01:00 UTC and each relate to the period remaining until 12:00 UTC. The prediction consists of a text, a map with categories and probability of occurrence and a diagram of the probabilities. The One -Day Forecast provides the only concrete probabilities for tornadoes, hail and strong winds. It is by all predictions that the most detailed with the forecasts and the highest accuracy.
The prediction for two days will be issued daily at 08:00 UTC and 17:30 UTC and is valid for 24 hours from 12:00 UTC of the following day. It contains only a basic assessment with a text and a diagram of the general probability of thunderstorms. It is very unusual that a two -day forecast already warning of moderate hazards. A warning of large risks were only available on 7 April 2006.
The prediction for three days includes the same issues as the two -day forecast. Since accurate forecasts with a longer period of time are more difficult, warnings higher categories three days in advance are rare. Before even dangers, only five times has been in a three -day forecast warned ( 10 June 2005 to January 2, 2006, April 24, 2007 June 6, 2007 and 7 July 2007). Previously, there was no warning of great danger.
The predictions for four to eight days consist mainly of text and can completely change the day is out, because accurate forecasting over such a long period is not reliably possible today. Maps show only areas with a risk of at least 30 % and are only very rarely due to the forecast difficulties for use. The longer-term predictions were until 22 March 2007 at the experimental stage. Since they belong to the official forecasts.
Local weather services of the National Weather Service, radio and television stations, and emergency planners rely on the predictions often to assess the risks to their region.
The following table shows the warnings issued depending on the nature of the storm duration or until the occurrence and the probability of occurrence within 40 km. (H = hatched area, the probabilities of 2% and 10 % are used only for tornadoes. )
¹ warning, the level SLGT have, if only the risk for tornadoes exists (this is usually the result of a tropical cyclone ). ² warning is not issued for Day 3.