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Showing content with the highest reputation since 02/03/20 in Articles

  1. A first look at how to use 500mb anomaly charts to help try and predict the weather These are notes from about 8 years ago. I have tried to check through to avoid any mistakes in the original text! First off what are they, well as they say the heading on the tin explains. They are at 500mb, roughly 18,000ft, and show the predicted contour lines, green in the case of NOAA charts and black (by and large) for ECMWF-GFS charts. The dashed red or blue lines, on the NOAA charts, with numbers on them are the predicted anomalies, hence the title, of heights in the areas shown by the das
    6 points
  2. There's been a lot of focus on 850mb temperatures over the last few days and will they/won't they support snowfall, so just wanted to create a post for any of the less experienced members who are probably left scratching their heads about the conflicting views amongst different members and want to know what to believe. Let's start with why everyone looks for the -6c 850mb (or hPa) line and it's a bit of a history lesson I'm afraid. I believe in terms of these (and other) forums, the magical figure of -6c was really coined as the "snow line" back in the bad old days of the late 90's and ea
    6 points
  3. This special COVID-19 Pandemic research topic is intended to be a resource for: help, advice and Government guidance (listed below) links to stats, facts and figures (listed below) scientific papers, reports and articles (now listed on a separate page here) New material will be continually added, so please check back frequently. If you have any comments, encounter any problems with this page, or have another source of information to add, please message me or reply to this topic. Thank you. -------------------------------------------------------------------------
    6 points
  4. A revised version of the earlier "Winter Snow Setups/Non-Snow Setups" topics, this goes through the range of winter setups we can get. As in summer, the main determining factors in what sort of winter weather we get are the positioning and strength of the jet stream. A strong jet stream means that depressions will frequently move from west to east, giving a "zonal" pattern over the UK. Because the Atlantic is relatively warm and moist, assisted by the warm North Atlantic Drift, zonal types often tend to be mild- but not always. A weak jet means lows track less frequently from west to
    3 points
  5. There was already a guide written by me about UK thunderstorm set-ups, but it was done some 10+ years ago now and I've felt for a while that it needed a re-vamp and updating to make a more comprehensive guide to the processes that produce the various types of thunderstorms we see in the UK. So here it is ... the Netweather guide to thunderstorms in the British Isles .... 15 pages long: Thunderstorms in the British Isles.pdf
    2 points
  6. The Arctic Oscillation Arctic Oscillation is an important lead on expected winter conditions in the Northern Hemisphere, loosely described as negative ( colder ) positive ( milder). The image below gives you a great contrast of a winter we will all easily recall with an extremely negative AO and a little further back a winter at the opposite end of the scale. When considering the overall forecast for Winter it is important to note any variables which provide clues as to which end of the scale the AO will tip towards, this in turn informs us of potential for blocking episodes
    2 points
  7. Hi all I promised to give this guide, so here it is. Its not complete and it is for those who are new to trying to work out this very difficult question. What to look for to get snow at sea level. (1) in showers (2) frontal weather (1) In showers 1) Dry bulb temperature below 5C, often 3C is a better mark 2) Dewpoint at or below zero 3) wet bulb temperature, if you have a weather station, no more than about 2C 4) 1000-500mb thickness (DAM) less than 522dm, lower if you are on the coast, but as high as 540dm it is possible in a heavy shower, but
    1 point
  8. The main Air Masses that affect the United Kingdom Air Masses are defined as a large body of air (covering many thousands of square kilometers) which at any given level has almost uniform temperatures, lapse rates(see topic on this), and humidity. Their Source Regions are large areas of the earth where air often stagnates for long periods. Examples of these are the Polar Regions, and the sub tropics. Air over any of these regions may stay for long periods and thus picks up the characteristics of the land or sea beneath it. When, because of a pressure gradient (see another topic
    1 point
  9. For those that have read Steve's interesting post and his reference to shortwaves here's a description courtesy of weatherprediction. com. PRESSURE TROUGHS AND SHORTWAVES METEOROLOGIST JEFF HABY When analyzing a surface chart you will notice the isobars bend in the vicinity of the warm front and the cold front. The isobars do not make perfect circles around low-pressure centers because of the pressure troughs created by the fronts. Pressure can decrease in the atmosphere by: (1) causing the air to rise (2) decreasing the density of the air (3) decreasing the mass
    1 point
  10. I hope the article below will help to explain what the term means and how its value is arrived at. The term DAM is used at times but its correct term is 'thickness' between the two levels in the atmosphere. Remember although its often referred to at the 1000-500mb level it can be used between any two levels. For snow forecasting the other most often used is the 1000-850mb values. DAM heights or total thickness between two levels, usually the 1000mb and 500mb I hope this may help (!) to show how complex is the relationship but also how relatively easy it is, knowing the two heigh
    1 point
  11. The MJO is a major contributor to the global weather patterns, so for those who want to understand a little bit more about it here is a brief overview of my current understanding of the MJO and Rossby and Kelvin Waves. First lets talk a little bit about waves or more specifically Rossby and Kelvin waves. These can occur both in the Atmosphere and in the Ocean and it is important to be clear about the difference between the two. Oceanic Rossby waves take the form of slight height changes in the sea and more apparent changes in the depth of the thermocline. These can take months or yea
    1 point
  12. Ok I will start a new thread for dicussions along this line and perhaps I will draw on some ideas expressed in the stratospheric thread and artic sea ice thread. I guess you would be the best person to explain all this GP but for those who don't know this thread is about global angular momentum and how it oscialltes up and down (Global Wind Oscillation) along the lines discussed by Ed Berry. Angular momentum is of course a measure of the turning force in the winds, so could perhaps be considered a measure of the strength of low pressure systems, but also relates to how much the jetstream
    1 point
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