Keith (Southend) wrote:

Why do they not have thickness lines for the earlier ones?


Keith,

Martin Rowley very kindly answered this for me in a post dated 21st
January, as follows:



"Tom Bennett" wrote in message
...
Looking at the previous thread has prompted me to ask something I've
been
wondering about for a while. Why doesn't thickness appear on any of
the
forecast charts until T +36 hrs and later? (I'm looking at the UKMO
charts on Wetterzentrale).


I'll answer this question from the information that I know, but
emphasise that there are others who look in to this newsgroup who could

add more detail and perhaps correct some of the below .. though I think

the broad thrust of the answer is correct:-....................

The question should be:.... "why *do* the charts beyond T+24 have
thickness isopleths on them?"


In days long ago, there were only the Baratic (T+0) and the Prebaratic
(T+24). (before my time I hasten to add).


In association with these, upper air charts were issued, both analysis
and forecast (Contour / Prontour), in coded and chart format - the
latter more widely as facsimile was developed.


There was _no need_ to add thickness lines to the Baratic/Prebar
surface
charts - forecasters would have separate charts for same - indeed many
outfield forecasters would independently both analyse and 'prog' such
and draw their own conclusions to add to (or deviate from) the guidance

from Dunstable/Bracknell, using the work of Sutcliffe & Forsdyke.


When the T+48/T+72 came along (can't remember when ... certainly in use

by the late 1960's as I was heading up FAX charts for them every night)

then the only way to indicate broad-scale thermal distribution was by
adding the isopleths of thickness. This practice was continued when
T+96/120 were introduced (again, memory hazy ... could be late
1970's?).


In this time, there was no Internet, no ODS, no Horace, no Nimbus etc.,

etc. and production of upper air forecasts in chart format beyond T+24
would have clogged up the land-line FAX circuits too much (remembering
that hourly/3-hourly charts had to be broadcast, along with plotted
tephigrams, upper wind sheets and a whole host of other output - all
taking up sizeable slabs of broadcast time.)


It wouldn't have seemed odd to Met Office users NOT to have thickness
on
the ASXX/FSXX - it only seems so now because of the changing times.
(And
as Jon has noted elsewhere, for Radiofax use, where reception could be
'iffy' at times, they might have clashed with all the labels,
continuity, tracking, 35kn plots etc.)


Whether there will be any move to put thickness on the T+24, I'm not so

sure; there is no good operational reason for doing this as
'mainstream'
users can pull up the associated TTHK and, more importantly, much
*better* air mass tracers like ThetaW fields to use for things like
expected temperatures, snow risk etc.


Martin.