India Meteorological Dept press release
Posted by CypressTX on 4/15/2010, 1:40 pm
http://www.imd.gov.in/section/nhac/dynamic/pressrelease.pdf (easier to read at the link)

Subject: Severe thunderstorm activity over West Bengal and adjoining Bihar
Severe thunderstorm activity meteorologically called Nor'westers and locally
known as Kalbaisakhi, is one of the most frequent climatological features of the premonsoon
season (March-May) over Chhattisgarh, Jharkhand, Bihar, West Bengal,
Orissa and northeastern states. The most common type is one which originates over
Bihar & Jharkhand and moves southeastwards towards West Bengal. These
localized severe thunderstorms in the form of squalls /tornadoes are devastating in
nature mainly because of very strong winds (more than 100 kmph) and also due to
sudden heavy downpour.
The favourable conditions for development of severe thunderstorms over
these areas are:
(i) Conditional instability
(ii) Availability of moist air at lower levels
(iii) Insolation and orography for initial lifting of moist air to higher levels
(iv) Presence of high lapse rate of temperature, due to dry westerly at upper levels
and moist southerly/southwesterly air at lower levels
(v) Presence of trough or cyclonic circulation in lower levels over the region
Weather conditions on 13 April 2010
A trough existed in lower levels from Bihar to northwest Bay of Bengal
causing moisture incursion over West Bengal. Satellite imagery of 1730 hrs IST on
13 showed deep convective clouds over East Bihar and Sikkim areas. It led to the
development of a severe thundercloud called cumulonimbus with its height upto 14
km. The clouds containing multiple cells got intensified and moved in East to South-
easterly direction. At 2247 hrs IST the vertical extent became more than 18 km. The
distance of the multiple cell system from Kolkata was 408 km in North-Northwest
direction. The cloud system further intensified into a squall line structure at 2317 hrs
IST and moved over Bhagalpur and Purnia region in Bihar and adjoining North
Bengal region. At 2332 hrs IST, the intensity of the system was maximum and this
is the probable time of devastation due to strong downdrafts with wind speed might
be exceeding 100 kmph. Thereafter, the system moved away and entered
Bangladesh almost in a squall line formation but with reduced intensity. Over all
duration of the system was about two hrs.
This severe thunderstorm with large vertical extent may be associated with a
tornado and the damage caused may be due to tornadic rotation associated with the
severe and tall thunderstorms.
Affected Districts
The preliminary reports indicate that it has affected mainly Dinajpur and
Jalpaiguri districts of West Bengal and Kishanganj district of Bihar, as also revealed
by the visual media reports. There are reports of uprooting of trees, damage to
communication/ electric lines and also damage to many houses. There are also
reports of some causalities, the maximum loss is reported from Dinajpur district.
To know the severity and exact extent of damage, a team of experts of
India Meteorological Department has already been sent to the affected areas. The
detailed report will be submitted shortly.
Note: It is clarified that this was not a cyclonic storm as has been reported by
some of the media.
28
In this thread:
Cyclone kills 76 people in eastern India - Fred, 4/14/2010, 8:12 am
< Return to the front page of the: message board | monthly archive this page is in
Post A Reply
This thread has been archived and can no longer receive replies.