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Thickness and maximum surface temperatures

Approximate relationship between Thickness (or Relative Topography): 500 - 1000 hPa & the maximum screen temperature (oC) [ NW maritime Europe; also see cautionary notes below]

 Thickness 500-1000 hPa (in metres) Nil / Poor insolation (a) Moderate / High insolation (b) High summer:
strong sun
 5100  -6  -1  
 5150  -3  2  
 5200  -1  4  
 5250  2  7  
 5280  3  8  
 5300  4  9  
 5350  7  12  
 5400  9  14  15
 5450  11  16  17
 5460  12  17  18
 5500  14  19  20
 5550  16  21  22
 5600  19  24  25
 5640  21  26  27
 5650  21  26  27
 5700  24  29  30
 5750  26  31  32
 5800  29  34  35
 5820  30  35  36

Notes:
(a): Generally overcast, thick cloud cover - minimum effective insolation; also generally applicable to the mid-winter period of low solar angle. Precipitation would imply the figure might be a degree or two lower still.
(b): Fine, sunny much of the time up to day-maximum occurrence. If the sunshine is particularly strong in spring & summer, then this figure may be a couple of degrees (at least) higher. These figures though would NOT apply to mid-winter, low solar-angle events.
(c): In mid-winter, with low thickness values in particular, temperatures will be lower still - perhaps by as much 5degC due to limited insolation.

These figures are based on the theoretical relationship between the average lapse rate within the lower troposphere (2 degC/1000ft) and the implied mean temperature (within the layer 500 - 1000 hPa) given by the total thickness values. They take no account of the type of surface (sea, dry land, snow-cover etc.) and also there is no allowance for seasonal variation of solar energy available.
Sunny figures further imply that a dry adiabatic lapse rate (3 degC/1000ft) exists at time of maximum temperature from the surface to 850 hPa.

However, this is a very crude relationship, and the figures given above should be regarded as the rough 'limits' of expected maxima. In practice, they will vary by several degrees. This is why forecasting day maxima based on total thickness has fallen out of fashion.