Will Hand wrote:
snip-lots
I said in another thread that I thought that the 564 DAM line was
just a bit further north than it should be. snip
but the persistent closeness of that warm and moist 564 DAM air
is bothering me

"Keith(Southend)" wrote ...


Admittedly, I can't say where the 564 DAM line normally is this time
of year, but looking at the charts I don't see it being particularly
far north.
http://www.wzkarten.de/pics/brack0a.gif
http://www.wzkarten.de/pics/brack1a.gif
http://www.wzkarten.de/pics/brack3.gif
and in the middle of the Atlantic it seem quite far south. Certainly
it's close to us on the near Continent, but am I missing something
here?

.... I've posted the mean 500-1000 hPa thickness (ex. NOAA/ESRL) he-

http://freespace.virgin.net/martin.r...HK_JULmean.gif

I've also looked at the last 8 days of analysis using the wetter3.de
archive. You can see from the mean chart for July that there is a
thermal trough with an axis roughly along 20degW at latitude ~
40/45degN, which I assume is the area that we are talking about?

For the last 8 days, the mean value of thickness at a point 41N, 20W
(where the mean for 1968-1996 is given as 564 dam), was 565dam: +1dam
over the long-term mean. This doesn't seem to me to show anything
excessively warm. Of the last 8 days, 5 had 00Z values at or below
564dam, with a temporary peak (passing wave) of 573 dam.

I also looked at a couple of other warm Julys (warm in BI that is:
July 1995 is one example), and the mean 564 dam contour was
comfortably further north than this mean - typically lying from Nova
Scotia to Greater Paris, with a dip in the 15-25degW area. Given that
these are *mean* values, the day-to-day position must have been even
further north than that for extended periods.

I can't see from any data that I have available that there is anything
particularly unusual about the latitudinal position of the 564dam
contour.

Martin.


--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023