"Mike Tullett" wrote :

I agree about the low, Jon. Warmer air was sucked in to it when it was
near Iceland. I recall, many years ago, there was a debate on just
important baroclinic factors were in the development of polar lows. But
it's a long time since I read the literature on the subject.

"just important baroclinic factors" should read
"just how important baroclinic factors were in the development of polar
lows"

Found it .... "The Polar Low as a Baroclinic Disturbance",
TW Harrold and KA Browning, QJRMetS, 95, 1969, pp710-723.

The intro reads:
"This paper describes the 3-dimensional airflow and precipitation within
small 'polar' depressions which sometimes cross Britain during N-ly
outbreaks and which in winter can be responsible for heavy snowfalls.
The data used in the study consist of Doppler and conventional radar
information, together with routine synoptic data and sequential radiosonde
ascents from the radar station. 3-dimensional airflow was derived from
the radisonde data assuming that wet bulb potential temperature was
conserved. Horizontal and vertical air velocities were also derived from
the Doppler radar measurements.
Previous knowledge of polar lows is meagre; they are generally thought
to be shallow features resulting from enhanced convection within cold air
flowing over a warm sea. However, the well-developed polar low
which is the main subject of this paper is shown to have been an essentially
baroclinic disturbance. Although enhanced small-scale convection occurred in
one sector, the main area of widespread precipitation associated with the
polar low was produced not be smallscale convective overturning but rather
by slantwise convection within a narrow tongue of air ascending steadily
at about 10cm sec-1.
The speed of travel and short wavelength (9ookm) of the polar low in
this study are consistent with its having formed in a region of enhanced
baroclinicity within the polar air below 850mbar rather than in the major
baroclinic zone bounding the polar air mass. Considerable low-level
baroclinicity within the polar air is also shown to have been present during
the formation of other intense polar lows."

pe