Maximum Daytime Temperature (Tmax) from partial thickness (1000-850 hPa)

Maximum daytime temperature


Max Temperature : °C


Max temp range for cloud classes with selected thickness and date period:

Cloud Class Max Temp °C
0 :
1 :
2 :
3 :

Callen and Prescott method

This is an empirical technique based on the maximum temperatures observed at Gatwick and the 1000-850 hPa thickness values at midday at Crawley.

Three steps are involved:

  1. Obtain the 1000-850 hPa thickness value (gpm).
  2. Obtain the temperature adjustment for the time of year and cloud class from the graph.
  3. Apply this correction to uncorrected maximum temperature from thickness values to obtain Tmax

The relationship between 1000-850 hPa thickness values (h) and the unadjusted maximum temperature (Tu) is given by:
$$T_u = -192.65 + 0.156h$$

Cloud Class definitions and adjustment curves:

Cloud Class Definition
0 CL + CM ≤ 3/8, CH ≤ 5/8 or any fog confined to dawn period
1 CL + CM + CH = 4/8-6/8 or any fog clearing slowly during morning
2 CL + CM ≥ 6/8 or any fog clearing before noon
3 Predominantly overcast with precipitation (not including very slight drizzle) or persistent fog
Correction graph


Unadjusted maximum temperature (°C) from thickness (gpm):

0 1 2 3 4 5 6 7 8 9
1220 -2.3 -2.2 -2.0 -1.9 -1.7 -1.6 -1.4 -1.2 -1.1 -0.9
1230 -0.8 -0.6 -0.5 -0.3 -0.1 0.0 0.2 0.3 0.5 0.6
1240 0.8 0.9 1.1 1.3 1.4 1.6 1.7 1.9 2.0 2.2
1250 2.3 2.5 2.7 2.8 3.0 3.1 3.3 3.4 3.6 3.8
1260 3.9 4.1 4.2 4.4 4.5 4.7 4.8 5.0 5.2 5.3
1270 5.5 5.6 5.8 5.9 6.1 6.3 6.4 6.6 6.7 6.9
1280 7.0 7.2 7.3 7.5 7.7 7.8 8.0 8.1 8.3 8.4
1290 8.6 8.7 8.9 9.1 9.2 9.4 9.5 9.7 9.8 10.0
1300 10.2 10.3 10.5 10.6 10.8 10.9 11.1 11.2 11.4 11.6
1310 11.7 11.9 12.0 12.2 12.3 12.5 12.6 12.8 13.0 13.1
1320 13.3 13.4 13.6 13.7 13.9 14.1 14.2 14.4 14.5 14.7
1330 14.8 15.0 15.1 15.3 15.5 15.6 15.8 15.9 16.1 16.2
1340 16.4 16.5 16.7 16.9 17.0 17.2 17.3 17.5 17.6 17.8
1350 18.0 18.1 18.3 18.4 18.6 18.7 18.9 19.0 19.2 19.4
1360 19.5 19.7 19.8 20.0 20.1 20.3 20.4 20.6 20.8 20.9
1370 21.1 21.2 21.4 21.5 21.7 21.9 22.0 22.2 22.3 22.5
1380 22.6 22.8 22.9 23.1 23.3 23.4 23.6 23.7 23.9 24.0
1390 24.2 24.3 24.5 24.7 24.8 25.0 25.1 25.3 25.4 25.6
1400 25.8 25.9 26.1 26.2 26.4 26.5 26.7 26.8 27.0 27.2
1410 27.3 27.5 27.6 27.8 27.9 28.1 28.2 28.4 28.6 28.7
1420 28.9 29.0 29.2 29.3 29.5 29.7 29.8 30.0 30.1 30.3
1430 30.4 30.6 30.7 30.9 31.1 31.2 31.4 31.5 31.7 31.8
1440 32.0 32.1 32.3 32.5 32.6 32.8 32.9 33.1 33.2 33.4
1450 33.6 33.7 33.9 34.0 34.2 34.3 34.5 34.6 34.8 35.0
1460 35.1 35.3 35.4 35.6 35.7 35.9 36.0 36.2 36.4 36.5
1470 36.7 36.8 37.0 37.1 37.3 37.5 37.6 37.8 37.9 38.1
1480 38.2 38.4 38.5 38.7 38.9 39.0 39.2 39.3 39.5 39.6
1490 39.8 39.9 40.1 40.3 40.4 40.6 40.7 40.9 41.0 41.2
1500 41.4 41.5 41.7 41.8 42.0 42.1 42.3 42.4 42.6 42.8