|
The example of the 30
October storm
The changes in weather features which took place in
southern England on 30 October, were a typical example
of the marked changes that can happen when an intense
and well-developed frontal system passes over during the
winter months. The table below shows the typical changes
that occur in weather features. Table 1. The typical changes in
weather features associated with the passage of a mature
depression across the UK in the winter months
| |
Ahead of the warm front |
The passage of the warm
front |
The warm sector |
The passage of the cold
front |
The cold sector |
|
Pressure |
starts
to fall steadily |
continues to fall |
steadies |
starts
to rise |
continues to rise |
|
Temperature |
quite cold, starts to
rise |
continues to rise |
quite mild |
sudden drop |
remains cold |
|
Cloud cover |
cloud
base drops and thickens (cirrus and
altostratus) |
cloud
base is low and thick (nimbostratus) |
cloud
may thin and break |
clouds
thicken (sometimes with large cumulonimbus) |
clouds
thin with some cumulus |
|
Wind speed and
direction |
speeds increase and
direction backs |
veers and becomes
blustery with strong gusts |
remain steady, backs
slightly |
speeds increase,
sometimes to gale force, sharp veer |
winds are squally |
|
Precipitation |
none at
first, rain closer to front, sometimes snow on
leading edge |
continues, and sometimes heavy
rainfall |
rain
turns to drizzle or stops |
heavy
rain, sometimes with hail, thunder or sleet |
showers |
| The passage of the warm
and cold front can be seen clearly on Figs 5, 6
and 7, which show the synoptic pressure charts
for 0000, 0600 and 1200 UTC on 30 October. |
 |
|
Figure 5. 0000 UTC, 30
October 2000 |
|
Figure 6. 0600 UTC, 30
October 2000 |
 |
|
Figure 7. 1200 UTC, 30
October 2000 |
 |
Table 2 shows the changes
in rainfall amounts and temperature that took place
every hour at the weather station at Heathrow Airport
between 1000 on 29 October and 1700 on 30 October. The
changes can be easily linked with the passage of this
depression. Temperatures start to rise as the warm front
passes over in the early hours of 30 October. They
remain high until around 0600, as the warm sector passes
over. Further rain occurs as the warm air is undercut by
descending cold air from the occlusion. A sharp decrease
in temperatures takes place as the cold front approaches
around 0700. A heavy period of rain then occurs as this
front passes over, before easing off in mid-morning as
the cold sector passes over behind the warm front.
|
Date |
Time |
Rainfall amount
(mm) |
Dry bulb temp
(°C) |
|
29/10/00 |
1000 |
0.0 |
10.0 |
|
29/10/00 |
1100 |
0.0 |
10.8 |
|
29/10/00 |
1200 |
0.0 |
11.6 |
|
29/10/00 |
1300 |
0.0 |
11.6 |
|
29/10/00 |
1400 |
0.0 |
11.8 |
|
29/10/00 |
1500 |
0.0 |
11.6 |
|
29/10/00 |
1600 |
0.0 |
10.5 |
|
29/10/00 |
1700 |
0.2 |
10.8 |
|
29/10/00 |
1800 |
1.6 |
11.4 |
|
29/10/00 |
1900 |
2.0 |
12.1 |
|
29/10/00 |
2000 |
2.4 |
11.7 |
|
29/10/00 |
2100 |
2.4 |
12.7 |
|
29/10/00 |
2200 |
1.6 |
13.2 |
|
29/10/00 |
2300 |
0.8 |
11.4 |
|
30/10/00 |
0000 |
5.4 |
13.1 |
|
30/10/00 |
0100 |
2.4 |
13.3 |
|
30/10/00 |
0200 |
2.4 |
13.2 |
|
30/10/00 |
0300 |
1.6 |
13.1 |
|
30/10/00 |
0400 |
1.6 |
13.0 |
|
30/10/00 |
0500 |
2.0 |
13.1 |
|
30/10/00 |
0600 |
1.4 |
12.8 |
|
30/10/00 |
0700 |
2.8 |
9.8 |
|
30/10/00 |
0800 |
5.0 |
10.2 |
|
30/10/00 |
0900 |
1.0 |
8.9 |
|
30/10/00 |
1000 |
0.0 |
8.4 |
|
30/10/00 |
1100 |
0.0 |
6.6 |
|
30/10/00 |
1200 |
0.2 |
7.6 |
|
30/10/00 |
1300 |
0.4 |
9.9 |
|
30/10/00 |
1400 |
0.2 |
10.8 |
|
30/10/00 |
1500 |
0.0 |
11.3 |
|
30/10/00 |
1600 |
0.0 |
11.0 |
|
30/10/00 |
1700 |
0.0 |
10.5 |
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