Is the type of fog we are experiencing in the North Midlands radiation fog? Just been reading about fog and the current weather conditions.

On 16/01/2013 06:44, Wendy Tinley wrote:
Is the type of fog we are experiencing in the North Midlands radiation fog? Just been reading about fog and the current weather conditions.

There are two kinds of fog, radiation and advection. Radiation fog
require clear skies, near calm winds (to provide some mixing) and a
sufficiency of moisture.
Advection fog occurs when warm air moves over cold ground, so e.g. when
a warm front moves in over cold ground after a number of hard frosts.
This is a simplistic explanation, but will suffice.
It can be quite difficult to forecast - e.g. Gatwick is in a fog hollow
(brilliant for an airport!). When I did weather observing at Heathrow,
we had to watch for fog forming over the reservoirs and drifting over
the airport - when it might start to dissipate because of the heat
island effect of the centre.
Your fog would appear to be radiation.

Cheers

Malcolm

On 16/01/2013 08:52, Metman2012 wrote:
On 16/01/2013 06:44, Wendy Tinley wrote:
Is the type of fog we are experiencing in the North Midlands radiation
fog? Just been reading about fog and the current weather conditions.

There are two kinds of fog, radiation and advection. Radiation fog
require clear skies, near calm winds (to provide some mixing) and a
sufficiency of moisture.
Advection fog occurs when warm air moves over cold ground, so e.g. when
a warm front moves in over cold ground after a number of hard frosts.
This is a simplistic explanation, but will suffice.
It can be quite difficult to forecast - e.g. Gatwick is in a fog hollow
(brilliant for an airport!). When I did weather observing at Heathrow,
we had to watch for fog forming over the reservoirs and drifting over
the airport - when it might start to dissipate because of the heat
island effect of the centre.
Your fog would appear to be radiation.

Cheers

Malcolm

Thanks Malcolm... from what I'd read I thought it had to be radiation
but just needed to seek confirmation from 'edukatered people'.

--
Wendy Tinley
Sheffield

On Wednesday, January 16, 2013 6:44:46 AM UTC, Wendy Tinley wrote:
Is the type of fog we are experiencing in the North Midlands radiation fog? Just been reading about fog and the current weather conditions.

Hi Wendy

Did you have any ice crystals falling out the fog during the morning?
All surfaces were coated around the Rotherham area.

Simon S (South Yorkshire)

On Wednesday, January 16, 2013 8:52:47 AM UTC, Metman2012 wrote:
On 16/01/2013 06:44, Wendy Tinley wrote:

Is the type of fog we are experiencing in the North Midlands radiation fog? Just been reading about fog and the current weather conditions.



There are two kinds of fog, radiation and advection.

What about sea fog?

On 16/01/2013 21:36, willie eckerslike wrote:
On Wednesday, January 16, 2013 8:52:47 AM UTC, Metman2012 wrote:
On 16/01/2013 06:44, Wendy Tinley wrote:

Is the type of fog we are experiencing in the North Midlands radiation fog? Just been reading about fog and the current weather conditions.
There are two kinds of fog, radiation and advection.
What about sea fog?


Most sea fog is advection fog. Warm moist air runs over cool sea whose
surface temperature is below the dewpoint temperature of the air.

But you could have asked "What about hill fog?". Whilst some of this is
due to low cloud being blown onto hills which project above cloud base,
hills also produce their own fog by the following:

1) Forced ascent of air, which is lifted above its condensation level
on windward slopes.

2) Sun warmed hill slopes generating cumulus clouds which may blanket
the summits whilst the low ground around remains sunny.

Both of these can be seen quite frequently in the hillier parts of our
islands.

--
- Yokel -

Yokel posts via a spam-trap account which is not read.

On Wednesday, January 16, 2013 10:13:13 PM UTC, Yokel wrote:
On 16/01/2013 21:36, willie eckerslike wrote:

On Wednesday, January 16, 2013 8:52:47 AM UTC, Metman2012 wrote:

On 16/01/2013 06:44, Wendy Tinley wrote:



Is the type of fog we are experiencing in the North Midlands radiation fog? Just been reading about fog and the current weather conditions.

There are two kinds of fog, radiation and advection.

What about sea fog?





Most sea fog is advection fog. Warm moist air runs over cool sea whose

surface temperature is below the dewpoint temperature of the air.




Thanks for that, but it seems not to explain the sharp edges that North Sea fog has on occasion, or the isolated but regular days when radiation fog over south Dorset drifts out over Lyme Bay and not only becomes sea fog but expands its area when clear of the coast.

There are two kinds of fog, radiation and advection.
What about sea fog?
Most sea fog is advection fog. Warm moist air runs over cool sea whose
surface temperature is below the dewpoint temperature of the air.
Thanks for that, but it seems not to explain the sharp edges that North
Sea fog has on occasion
That is due to very small variations in sea surface temperature or low-level
humidity
or the isolated but regular days when radiation fog over south Dorset
drifts out over Lyme Bay and not only becomes sea fog but expands its area
when clear of the coast.
This is advection fog - moist air moving out to sea. Probably expanding due
to further evaporation of moisture from the sea surface.
--
Freddie
Bayston Hill
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/#!/BaystonHillWx for hourly reports

On Thursday, January 17, 2013 9:52:46 AM UTC, Freddie wrote:
There are two kinds of fog, radiation and advection.

What about sea fog?

Most sea fog is advection fog. Warm moist air runs over cool sea whose

surface temperature is below the dewpoint temperature of the air.

Thanks for that, but it seems not to explain the sharp edges that North

Sea fog has on occasion

That is due to very small variations in sea surface temperature or low-level

humidity

or the isolated but regular days when radiation fog over south Dorset

drifts out over Lyme Bay and not only becomes sea fog but expands its area

when clear of the coast.

This is advection fog - moist air moving out to sea. Probably expanding due

to further evaporation of moisture from the sea surface.


Thanks. It has always intrigued me why the fog does not disperse in winter when moving over sea temperatures that are higher than the land, but I have noticed it persist for two or three days; a number of times over the last few years.

On 16/01/2013 21:09, Simon S wrote:
On Wednesday, January 16, 2013 6:44:46 AM UTC, Wendy Tinley wrote:
Is the type of fog we are experiencing in the North Midlands radiation fog? Just been reading about fog and the current weather conditions.

Hi Wendy

Did you have any ice crystals falling out the fog during the morning?
All surfaces were coated around the Rotherham area.

Simon S (South Yorkshire)


Hi Simon,

Didn't see any ice crystals... and the surfaces remained dry - apart
from the snow cover we still have.


--
Wendy Tinley
Sheffield