There are a couple of troughs marked on the 6z fax analysis chart, just
wondered if anyone knew how they are charted as there is no isobar variation
so presumably they are upper troughs. Are they deduced from the radiosonde
measurements?

Thanks.

Almost all forecasting is based on model output these days. This also
includes many so called analised charts, which are produced automatically.
Features such as troughs and fronts are, I believe, still put on by
'humans', albeit on a screen without a pencil in sight.

--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html
"MichaelJP" wrote in message
...
There are a couple of troughs marked on the 6z fax analysis chart, just
wondered if anyone knew how they are charted as there is no isobar
variation
so presumably they are upper troughs. Are they deduced from the radiosonde
measurements?

Thanks.

"MichaelJP" wrote
There are a couple of troughs marked on the 6z fax analysis chart,
just
wondered if anyone knew how they are charted as there is no isobar
variation so presumably they are upper troughs. Are they deduced from
the radiosonde
measurements?
.... and
"Bernard Burton" wrote
Almost all forecasting is based on model output these days. This also
includes many so called analised charts, which are produced
automatically.
Features such as troughs and fronts are, I believe, still put on by
'humans', albeit on a screen without a pencil in sight.

.... unfortunately, we don't see the 'words' to go with the charts: the
Chief Forecaster (or whoever it is nowadays) at Exeter would often
explain in the routine 'guidance' issues how certain features were
located.

In this case, we can only surmise that the analyst's eyes were attracted
to the organised bands of heavy rainfall and associated 'string' of
cold-topped cloud etc., at the time of analysis.
As Bernard has indicated (above), the staff in a modern office now do
everything on the screen, so they can overlay not only the 'standard'
imagery (satellite, rainfall radar etc.), but also model diagnostics
such as vertical velocity, vorticity maxima, Q-vector divergence etc.,
and provided these provide a coherent sequence through a 3 - 6 hour time
period, it is often useful to mark such areas with 'something': in this
case a trough was deemed the correct line to use, as presumably (I
haven't looked in great detail), the features are contained within
essentially the same airmass.

Although on this output it is often not possible to find a classic
'trough' shape to the isobars, if you draw the isobars carefully at say
1.0hPa or perhaps 0.5hPa, often a trough can be found, albeit a very
weak disturbance of the synoptic isobaric flow. The radio-sonde network
is far too course to find the companion feature in the upper air, but
again, model diagnostics can be used as a 'proxy' for a radio-sonde
network.

Martin.

"Martin Rowley" m wrote in
message ...
"MichaelJP" wrote
There are a couple of troughs marked on the 6z fax analysis chart, just
wondered if anyone knew how they are charted as there is no isobar
variation so presumably they are upper troughs. Are they deduced from the
radiosonde
measurements?
... and
"Bernard Burton" wrote
Almost all forecasting is based on model output these days. This also
includes many so called analised charts, which are produced
automatically.
Features such as troughs and fronts are, I believe, still put on by
'humans', albeit on a screen without a pencil in sight.

... unfortunately, we don't see the 'words' to go with the charts: the
Chief Forecaster (or whoever it is nowadays) at Exeter would often explain
in the routine 'guidance' issues how certain features were located.

In this case, we can only surmise that the analyst's eyes were attracted
to the organised bands of heavy rainfall and associated 'string' of
cold-topped cloud etc., at the time of analysis.
As Bernard has indicated (above), the staff in a modern office now do
everything on the screen, so they can overlay not only the 'standard'
imagery (satellite, rainfall radar etc.), but also model diagnostics such
as vertical velocity, vorticity maxima, Q-vector divergence etc., and
provided these provide a coherent sequence through a 3 - 6 hour time
period, it is often useful to mark such areas with 'something': in this
case a trough was deemed the correct line to use, as presumably (I haven't
looked in great detail), the features are contained within essentially the
same airmass.

Although on this output it is often not possible to find a classic
'trough' shape to the isobars, if you draw the isobars carefully at say
1.0hPa or perhaps 0.5hPa, often a trough can be found, albeit a very weak
disturbance of the synoptic isobaric flow. The radio-sonde network is far
too course to find the companion feature in the upper air, but again,
model diagnostics can be used as a 'proxy' for a radio-sonde network.

Martin.

Thanks, interesting - so even a feature that is barely recognisable as a
trough in the MSLP isobars is enough to provide significant weather in
situations like today?

"MichaelJP" wrote in message
...

Thanks, interesting - so even a feature that is barely recognisable as
a trough in the MSLP isobars is enough to provide significant weather
in situations like today?

.... often the way - even with 'classical' fronts, the 'weather' doesn't
necessarily run along, or even close-to the surface frontal boundary:
bands of rain can and do occur well away from, and at a different
alignment to, the 'classic' Norwegian frontal structure. The forcing is
in the upper air, whether around 3 - 5 km for many convective events, or
even higher (jet stream levels ~ 9 - 10km) for broad-scale events. This
is why meteorology didn't progress much until it was possible to monitor
and understand what was happening in the upper air - you might find some
of the stuff buried in here of interest:-

http://homepage.ntlworld.com/booty.w.../Sutcliffe.htm


Martin.


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