I was asked what the total thickness (500-1000hPa) was in August 2003
when we got the 'record' temperatures.

Based on NCEP re-analysis data (via Wetterzentrale)
10th August, 2003 (00GMT)

.... thickness (total/500-1000) = 573 dam

Based on Royal Met. Soc 'Weather Log' data for Herstmonceux

10th August, 2003 (12GMT)

.... thickness (total/500-1000) = 5728m (or 573 dam)

.... partial thickness (850-1000) = 1429 m

.... 850 temperature = +21degC

.... 850 thetaW (v. approx.) = 20 or 21degC

On that day, maxima reached 38degC across the (inland) SE of England.

Using Callen & Prescott's method (based on Gatwick/Crawley data), the
1429 m partial thickness (above) implies a 'base' temperature of
30.3degC, to which you add (for early August) a clear-sky correction of
+3.5, giving ~34degC; and locally, given strong insolation & ideal
conditions, a couple of degrees on top of that: in the event, the final
'record' was some 2C above that.

Using a rough scheme based on the 850T (5000ft, 2C/1000ft 'average',
3C/1000ft DALR), gives values at the notional surface between 31 & 36C,
which in this case would have given a good working guide.

/////

In this situation (mid-July 2006), using the GFS 06Z output (via the
'Ready' site), we get total thicknesses up to 568-570 (two or three dam
below those of 10th August 2003), and the 850-1000hPa partial
thicknesses peak at ~1420m, generally being in the range 1395-1410m
(again below those of the August '03 event).

Using the highest figure (1420m) gives uncorrected values (for somewhere
in the Crawley/Gatwick area) of 29C, then a mid-July correction of +4C =
33C, then a couple of degrees on top for a 'fudge' factor (~35C) &
locally a scraping more (the big unknown atm is how the baked-dry
surface & lack-lustre vegetation is going to respond).

The July 'record' of 35.9degC on the 3rd July 1976 in Cheltenham is
certainly at risk, but the 2003 'record of records' is probably not ....
yet!!

Martin.


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