I was wondering if today's proceedings constituted a proper polar low.

It seems that the snow arrived in the South East at just the right
time (at a cold night, just before daybreak). I also noticed on the
radar that the shallow low seemed to be winding itself just to the
west of London - prolonging the precipitation.

My last question is why did we have to wait until April 6th for the
first proper snow of the winter (in London)? - though there was
appreciable amounts of snow I'm sure there was enough energy from the
sun through the clouds to effect a thaw - something which would not
have happened in January...

The other thing I would like to know is why was it snowing here with a
temperature of +3c when had it have been January, it would have been rain at
that temperatuure.

I have noted this on a number of occasions, in other words it never seems to
have to be so cold for spring snow as it does for winter snow. Anyone out
there know the reasons why?

Regards.
Len.

"Scott W" wrote in message
...
I was wondering if today's proceedings constituted a proper polar low.

It seems that the snow arrived in the South East at just the right
time (at a cold night, just before daybreak). I also noticed on the
radar that the shallow low seemed to be winding itself just to the
west of London - prolonging the precipitation.

My last question is why did we have to wait until April 6th for the
first proper snow of the winter (in London)? - though there was
appreciable amounts of snow I'm sure there was enough energy from the
sun through the clouds to effect a thaw - something which would not
have happened in January...

My last question is why did we have to wait until April 6th for the
first proper snow of the winter (in London)?
------------------------
It's just not good enough, I shall write to the Telegraph.

Colonel Dave C (retired), Tunbridge Wells. ;-)

"Len Watts" wrote in message
...
The other thing I would like to know is why was it snowing here with a
temperature of +3c when had it have been January, it would have been rain
at that temperatuure.

I have noted this on a number of occasions, in other words it never seems
to have to be so cold for spring snow as it does for winter snow. Anyone
out there know the reasons why?

Regards.
Len.

------------
I'm not sure that for a few Januaries now we've had the coincidence of a
cold upper pool of air at the same time as the 850 hPa's were around -8C for
a while, as we did today in the S.E . Or maybe not at the same time as low
pressure with reasonable precipitation. I think today's synops would have
given snow in most winter months. Also, on some occasions it would be
because the sea temp could be 3C lower at this time of year than in January,
although I don't think this was a major factor today. I know that the
formula that Will once gave me of adding the dew point to temperature and
looking on a table for the percentage chance of snow worked well again for
me today. The dew point was relatively low and the two added together
remained below zero so high percent chance of snow. Perhaps "spring" snow is
more associated with heavy showers so the dew point might be lower and there
might be more evaporative cooling if the showers are heavy although the air
temp is higher either side of the showers.The experts may be able to
elaborate or add other reasons.
Dave

On Apr 6, 8:25 pm, Scott W wrote:
I was wondering if today's proceedings constituted a proper polar low.

It seems that the snow arrived in the South East at just the right
time (at a cold night, just before daybreak). I also noticed on the
radar that the shallow low seemed to be winding itself just to the
west of London - prolonging the precipitation.

My last question is why did we have to wait until April 6th for the
first proper snow of the winter (in London)? - though there was
appreciable amounts of snow I'm sure there was enough energy from the
sun through the clouds to effect a thaw - something which would not
have happened in January...

Early February we had a similar set up did we not? Similar time of
spell too, IIRC.

Didn't it have more to do with a joint Greenland High and a
Scandinavian Low?

Isn't it amazing what you can learn if you have Google Groups.

Concerning the air temperature during snow. It should be remembered that
snow flakes experience the wet bulb temperature of the air, not the dry bulb
one. In a situation like today's, with the wet bulb potential temperature
in the boundary layer of -1.0 to -1.5 over southern UK, no precipitation in
a solid state on leaving the cloud will be able to melt before reaching the
ground. Also, conditions of strong insolation can produce a marked
superadibatic lapse rate near the ground, on top of which, radiation effects
on the measuring probe or thermometer, be it in a screen or other shield,
can lead to snow being observed with reported air temperatures of +8 or so.

--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.woksat.info/wwp.html
or
www.btinternet.com/~wokingham.weather/wwp.html
"Len Watts" wrote in message
...
The other thing I would like to know is why was it snowing here with a
temperature of +3c when had it have been January, it would have been rain
at
that temperatuure.

I have noted this on a number of occasions, in other words it never seems
to
have to be so cold for spring snow as it does for winter snow. Anyone out
there know the reasons why?

Regards.
Len.

"Scott W" wrote in message
...
I was wondering if today's proceedings constituted a proper polar low.

It seems that the snow arrived in the South East at just the right
time (at a cold night, just before daybreak). I also noticed on the
radar that the shallow low seemed to be winding itself just to the
west of London - prolonging the precipitation.

My last question is why did we have to wait until April 6th for the
first proper snow of the winter (in London)? - though there was
appreciable amounts of snow I'm sure there was enough energy from the
sun through the clouds to effect a thaw - something which would not
have happened in January...

"Len Watts" wrote in message
...
The other thing I would like to know is why was it snowing here with a
temperature of +3c when had it have been January, it would have been rain
at that temperatuure.

I have noted this on a number of occasions, in other words it never seems
to have to be so cold for spring snow as it does for winter snow. Anyone
out there know the reasons why?


Whether precipitation will fall as snow depends more on the average
temperature of the air in which the precipitation is falling through
(related to the 1000-500mb thickness), rather than the surface temperature.
If the 100-500mb thickness is 516dm and the surface temperature is 5C then
precipitation is likely to be snow but if the thickness is 534dm and the
surface temperature is 2C then the precipitation is more likely to be rain.

It also depends on the humidity. If the air in which the snow is falling
through is fairly dry then as the snowflakes melt they will evaporate which
cools the surrounding air and retards the rate of melting.