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|Forecast Surface Pressure and Middle Atmosphere Maps|
GFS (left side) charts are sometimes unavailable due
to problems at COLA.
Click here for an alternative from Georg Mueller's Wetterzentrale.
These panels show forecast weather charts from four different models. GFS and GASP are medium range models and forecast for up to a week ahead. LAPS and MesoLAPS are short range models. In addition to showing surface pressure patterns, they give some basic information on action in the upper atmosphere which is just as important in deciding what the weather is going to do.
Be very careful to check the times and dates for which each model is valid. They are all run twice daily, based on data at midnight UTC (10am EST) and midday UTC (10pm EST). The times and dates on the charts are UTC. LAPS and MesoLAPS are updated between 12 and 2am and pm. GFS and GAPS are updated around 5am and 5pm. I have tried to align charts for the same periods, but they may be misaligned because of the different update times.
The layout of the charts is shown at right. You will need to use your horizontal slider bar to see them all. As a rule of thumb, the greater the agreement between the models, the more likely the forecast is to be accurate.
The charts from all four models show two sets of lines: surface pressure and thickness. Surface pressure isobars are shown as coloured on the GFS charts and solid on the others. Thickness lines -- black on GFS and dashed on the others -- indicate the average temperature through the lower 5km or so of the atmosphere. They measure the distance in dekametres (tens of metres) between the 1000 and 500 hPa pressure levels. The average distance is about 5.5km, or 5500 metres or 550 dekametres, which are the measures shown on the maps. Warm air is thicker than cold air, so lines marked 560 (or 5.6km) and above indicate that the bottom 5km or so of the atmosphere is fairly warm. A thickness below 540 (or 5.4km) indicates a pretty cold lower atmosphere, and below 530 is really cold!
If you are comfortable interpreting surface weather maps, try to become familiar with the upper situation too as upper "cold pools" and tongues of warm tropical air pushing down from the north are just as important as the surface pattern in deciding our weather.