0920z S F4-5 4km BR 7St004 8St006 05.6/05.2 1016.5
RMK: Min temp reached between 19 and 20z yesterday
when breeze picked up and disrupted inversion. Quite a
sharp wind this morning.

09-09: Tx 7.9 Tn -0.4 Tg -3.6 RR trace(w) sss 2.9

Philip Eden
Whipsnade 214m

On 15 Feb, 09:38, "Philip Eden" philipATweatherHYPHENukDOTcom wrote:

RMK: Min temp reached between 19 and 20z yesterday
when breeze picked up and disrupted inversion.
09-09: Tx 7.9 Tn -0.4 Tg -3.6 RR trace(w) sss 2.9

Hi, Philip,

Evening minima then mixing seem to be a feature of your site. The same
often happens here with light winds and minima two or three hours
after sunset on clear evenings. During the rest of the night the
temperature graph fluctuates with the katabatic wind which then
disappears just after sunrise when another dip in temperature occurs.
I assume it's a feature of hill country. Min last night was at 2030Z
yesterday evening before the katabatic and again at 0750Z after it
ceased.

The katabatic penetrates down to the Lead Mill for less time and
sometimes not at all.

Met O site 09-09 Tx 8.1 Tn -0.3 Tg -5.7 RR trace sss 7.3
Lead Mill 09-09 Tx 7.7 Tn -1.5

Ken
Copley 253metres, nr Barnard Castle, Teesdale, County Durham
http://copley.mysite

"Ken Cook" wrote :
On 15 Feb, 09:38, "Philip Eden" philipATweatherHYPHENukDOTcom wrote:

RMK: Min temp reached between 19 and 20z yesterday
when breeze picked up and disrupted inversion.
09-09: Tx 7.9 Tn -0.4 Tg -3.6 RR trace(w) sss 2.9

Evening minima then mixing seem to be a feature of your site. The same
often happens here with light winds and minima two or three hours
after sunset on clear evenings. During the rest of the night the
temperature graph fluctuates with the katabatic wind which then
disappears just after sunrise when another dip in temperature occurs.
I assume it's a feature of hill country. Min last night was at 2030Z
yesterday evening before the katabatic and again at 0750Z after it
ceased.

The katabatic penetrates down to the Lead Mill for less time and
sometimes not at all.

Met O site 09-09 Tx 8.1 Tn -0.3 Tg -5.7 RR trace sss 7.3
Lead Mill 09-09 Tx 7.7 Tn -1.5

Ken ... yes, it's been a revelation since I moved here. I think
I've read most of what's been published on frost hollows
(although I'm not sure how much of it I've retained!) but I
can't recall detailed comparisons of the characteristics of
different types of hollow.

If you stick Whipsnade into multimap (or whichever is your
map of choice) and look up the NGR square 00-01 18-19
you'll get a rough feel for the sort of country it is. I'm just 300m
walk from the top of the scarp slope which is 228m amsl, about
1km from the highest point hereabouts (243m), in a shallow
dry valley on the dip slope (the valley is no more than 10m
deep and the slopes have a gradient of about 1:10). The
katabatic catchment is probably less than 0.5km^2 but it
seems to work extremely efficiently for a couple of hrs after
the sun sets.

When the gradient wind is from the western half of the
compass the breeze picks up after only 2 or 3 hours
(katabatic assisted by gradient?) but on one evening last
week when the gradient wind was N to NEly, I didn't
reach my min until 21-22z - that was the -9°C which was
lower than most of the regular cold spots in Beds/Herts/
Bucks.

I'm still in temporary mode re instrumentation (no data-
logging AWS yet) but some time this year I aim to have
AWSs both in my garden and at the summit (and perhaps
eventually at the bottom of the scarp slope at the Gliding
Club too).

Endlessly fascinating, this climate stuff, isn't it?

Philip

"Philip Eden" philipATweatherHYPHENukDOTcom wrote :

0920z S F4-5 4km BR 7St004 8St006 05.6/05.2 1016.5
RMK: Min temp reached between 19 and 20z yesterday
when breeze picked up and disrupted inversion. Quite a
sharp wind this morning.

1250z S F4-5 15km 1Cu016 7Ci250 09.6/05.7 1015.7
RMK: St broke up between 10 and 1030z. Now tr of
Cu fra, tr of Sc ~030, 1Ci200 and 7Ci250.

Philip Eden
Whipsnade 214m

"Philip Eden" philipATweatherHYPHENukDOTcom wrote:
"Philip Eden" philipATweatherHYPHENukDOTcom wrote :

0920z S F4-5 4km BR 7St004 8St006 05.6/05.2 1016.5
RMK: Min temp reached between 19 and 20z yesterday
when breeze picked up and disrupted inversion. Quite a
sharp wind this morning.

1250z S F4-5 15km 1Cu016 7Ci250 09.6/05.7 1015.7
RMK: St broke up between 10 and 1030z. Now tr of
Cu fra, tr of Sc ~030, 1Ci200 and 7Ci250.

1550z S F5 40km 2Ac150 6Ci180 7Ci220 08.0/04.0 1013.8
RMK: Some depth of moisture at medium to high levels ...
what I have called Ci at 180 is clearly fibrous, but dense
in places with slight shading. Max appears to be 10.2 -
higher than I thought it would be here.

Philip Eden
Whipsnade 214m

"Philip Eden" philipATweatherHYPHENukDOTcom wrote in message
...
"Ken Cook" wrote :
On 15 Feb, 09:38, "Philip Eden" philipATweatherHYPHENukDOTcom wrote:

RMK: Min temp reached between 19 and 20z yesterday
when breeze picked up and disrupted inversion.
09-09: Tx 7.9 Tn -0.4 Tg -3.6 RR trace(w) sss 2.9

Evening minima then mixing seem to be a feature of your site. The same
often happens here with light winds and minima two or three hours
after sunset on clear evenings. During the rest of the night the
temperature graph fluctuates with the katabatic wind which then
disappears just after sunrise when another dip in temperature occurs.
I assume it's a feature of hill country. Min last night was at 2030Z
yesterday evening before the katabatic and again at 0750Z after it
ceased.

The katabatic penetrates down to the Lead Mill for less time and
sometimes not at all.

Met O site 09-09 Tx 8.1 Tn -0.3 Tg -5.7 RR trace sss 7.3
Lead Mill 09-09 Tx 7.7 Tn -1.5

Ken ... yes, it's been a revelation since I moved here. I think
I've read most of what's been published on frost hollows
(although I'm not sure how much of it I've retained!) but I
can't recall detailed comparisons of the characteristics of
different types of hollow.

If you stick Whipsnade into multimap (or whichever is your
map of choice) and look up the NGR square 00-01 18-19
you'll get a rough feel for the sort of country it is. I'm just 300m
walk from the top of the scarp slope which is 228m amsl, about
1km from the highest point hereabouts (243m), in a shallow
dry valley on the dip slope (the valley is no more than 10m
deep and the slopes have a gradient of about 1:10). The
katabatic catchment is probably less than 0.5km^2 but it
seems to work extremely efficiently for a couple of hrs after
the sun sets.

When the gradient wind is from the western half of the
compass the breeze picks up after only 2 or 3 hours
(katabatic assisted by gradient?) but on one evening last
week when the gradient wind was N to NEly, I didn't
reach my min until 21-22z - that was the -9°C which was
lower than most of the regular cold spots in Beds/Herts/
Bucks.

I'm still in temporary mode re instrumentation (no data-
logging AWS yet) but some time this year I aim to have
AWSs both in my garden and at the summit (and perhaps
eventually at the bottom of the scarp slope at the Gliding
Club too).

Endlessly fascinating, this climate stuff, isn't it?

Philip


It sure is.
I am completely confused at times by what goes on here, other than I know
that there is some sort of influence by the katabatic breeze. (I wish I'd
paid more attention at school.)
I'm slightly above the dry chalk valley floor, which runs approx N to S.
A log from yesterday /this morning.
Steady fall in temperature to:
2020 1.5c, brief breeze sets in.
2030 1.7c, breeze subsides.
2130 1.1c, breeze sets in.
2140 1.3c, breeze subsides.
2200 0.9c, breeze sets in.
2310 2.2c, breeze subsides.
0200 0.3c (night min), breeze sets in.
0330 2.2c, breeze subsides.
0420 1.2c, breeze sets in.
0530 2.4c, breeze persists.
0630 1.1c, breeze persists and temp continues to rise.

Eleven rise and falls???

--
David Mitchell, 70m amsl, Langtoft, East Riding of Yorkshire.

"Philip Eden" philipATweatherHYPHENukDOTcom wrote :
"Philip Eden" philipATweatherHYPHENukDOTcom wrote:
"Philip Eden" philipATweatherHYPHENukDOTcom wrote :

0920z S F4-5 4km BR 7St004 8St006 05.6/05.2 1016.5
RMK: Min temp reached between 19 and 20z yesterday
when breeze picked up and disrupted inversion. Quite a
sharp wind this morning.

1250z S F4-5 15km 1Cu016 7Ci250 09.6/05.7 1015.7
RMK: St broke up between 10 and 1030z. Now tr of
Cu fra, tr of Sc ~030, 1Ci200 and 7Ci250.

1550z S F5 40km 2Ac150 6Ci180 7Ci220 08.0/04.0 1013.8
RMK: Some depth of moisture at medium to high levels ...
what I have called Ci at 180 is clearly fibrous, but dense
in places with slight shading. Max appears to be 10.2 -
higher than I thought it would be here.

1850z S F5 30km 3Ac120 8Cs200 06.8/03.1 1013.7

09-18: Tx 10.2 RR nil sss(00-18) 4.1

Philip Eden
Whipsnade 214m

On 15 Feb, 12:38, "Philip Eden" philipATweatherHYPHENukDOTcom wrote:

Endlessly fascinating, this climate stuff, isn't it?

Hi, Philip and David,

Absolutely! I've lived in this area since the sixties and it still
fascinates me! Last Friday evening for instance. We had our usual R
Met Soc meeting in Durham (Adrian Hilton - climate change co-
ordinator, north-east) and Durham City (300ft asl) was wet, 3C and the
very occasional blob of sleet. I mentioned that snow had been falling
back home but by the look of things it would now be all gone. I could
not imagine that it would still be snow there.
The return journey home showed just how marginal our winters are and
how difficult it is to forecast snow. At 500ft asl wet snow lying in
patches, at 600ft wet snow cover, 700ft tricky road conditions with a
good snow cover, and at Copley rutted snow on the roads and 10cm
lying, -1C and 4x4 on the Jeep! By morning 15cm Copley, 27cm
Boltshope Park (1400ft, same as Dave at Howshill) and cars stranded on
local Pennine roads with the Fell Rescue in action.
You do get strange looks walking around the supermarket in wellingtons
in Bishop Auckland during these situations when there is only rain
there!


Ken
Copley, 253metres asl, nr Barnard Castle, Teesdale, County Durham
http://copley.mysite.orange.co.uk