Jet stream

Jet streams are fast flowing, narrow, meandering air currents found in the atmosphere of some planets, including Earth. On Earth, the main jet streams are located near the altitude of the tropopause and are westerly winds (flowing west to east). Their paths typically have a meandering shape. Jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including opposite to the direction of the remainder of the jet.

The strongest jet streams are the polar jets, at 9–12 km (30,000–39,000 ft) above sea level, and the higher altitude and somewhat weaker subtropical jets at 10–16 km (33,000–52,000 ft). The Northern Hemisphere and the Southern Hemisphere each have a polar jet and a subtropical jet. The northern hemisphere polar jet flows over the middle to northern latitudes of North America, Europe, and Asia and their intervening oceans, while the southern hemisphere polar jet mostly circles Antarctica all year round.

Jet streams are the product of two factors:

The Polar jet stream forms near the interface of the Polar and Ferrel circulation cells; while the subtropical jet forms near the boundary of the Ferrel and Hadley circulation cells.

Other jet streams also exist. During the Northern Hemisphere summer, easterly jets can form in tropical regions, typically where dry air encounters more humid air at high altitudes. Low-level jets also are typical of various regions such as the central United States. Meteorologists use the location of some of the jet streams as an aid in weather forecasting. The main commercial relevance of the jet streams is in air travel, as flight time can be dramatically affected by either flying with the flow or against. Clear-air turbulence, a potential hazard to aircraft passenger safety, is often found in a jet stream's vicinity, but it does not create a substantial alteration on flight times.

Northern hemisphere

Southern hemisphere

North america

North atlantic


Data source: GFS, California Regional Weather Server, Wikipedia



This wiki might help to use the full potential of Groenkloof weather website. The info section explains the hard and software and connections used.(In the menu bar under the sub menus Weather station and Groenkloof Weather) Weather data updates every minute.(for both the mobile and desktop sites) There is a mobile page with current conditions, forecast, forecast map, station history (with drop down menu for today, yesterday, month, year etc. showing all parameters) and lastly a graph with drop down menu for time period and parameter. (Very useful for quick references ) One can switch to the desktop page using the link in bottom right hand corner and vice versa. The desktop version is where very detailed weather info is available. ( Useful for more in depth detail ) It is divided in “blocks” The sunrise/sunset times and day length is shown. Moon with dates of full moon, new moon etc. The current block shows weather values in easy to read numerical format and updates every minute. “Live gauges” updates every minute and when the curser is hovered over a parameter it will show the min and max values and the time when this occurred. In the forecast maps one can use the menu bar top left of block to choose from windy or dark sky maps. Within the map one can choose from different parameters like wind, temperature, rain, thunder, clouds, pressure etc. Then station data is shown with now, max, min values and drop down menu for different time periods. There is also a history block where one can choose different parameters and a trends block with 1,3,6,12,24 hrs etc trends. Next is a forecast meteogram which is dynamic and moving the cursor over it will show all weather parameters at that point. Then easy to read forecast with dropdown the default using the Norwegian institute of meteorology values.(seems to be most accurate) Next is rainfall for today, this month, this year (from January) Drop down gives more options like seasonal(from September) etc. Rain balance is the stations values measured against 100 year rain data for Pretoria obtained from SA weather services. Next is graph with several drop down options and a day pie graph where one can pick dates and parameters. In extremes one can pick a parameter like absolute temperature, precipitation etc. to see max/min value dates and times. There is a air quality block click within block for more info. Map to show location of station. Webcam with view from Herbert Baker Street updates every 5 minutes. For aviation enthusiasts Cloud height time to sunset and density altitude. Then SA weather warnings from SA weather services, lightning detection and fire danger index. Followed by calendar, earthquakes and astronomical events. World weather...shows current conditions in few world cities. Database: data is stored every 5 mins and available data runs from January 2014. The menu at the top is really self explanatory and here there are countless information, statistics etc. Enjoy!! Leon P.S. since August 2021 I have added Solar, Uv sensors, Air Quality, soil moisture and lightning detection.





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