Jonathan D. Finch
Elevated Mixed Layer
Special Cases for the United States
Bengal Tornadoes--background information
Historical Tornado Tracks for East India and Bangladesh
Meteorological Charts for Historical Tornado Cases for Bengal
Latitudinal Comparison of the Geostrophic Wind Approximation
Assessing Instability on the Front Range Without Upper Air Data
Potential Temperature and Mixing Ratio--Contributions to CAPE on Elevated Terrain
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Forecasts will normally
be updated between 3 UTC and 6 UTC(0900-1200 BST) since surface based
is generally between 9 and 11 UTC. These are updated as needed through initiation time. In particularly active periods
I may update several times per day. If violent tornadoes are expected, I will try to issue tornado watch boxes before events
2006 Convective Outlooks
Discussion: updated 0520 UTC April 02 2006
The latest surface observations from Kurtimola showed 90F/76F with ssw wind at 12mph. Notcurnal storms
rolled across Meghalaya, India near Dhubri and Cherrapunji all night, undoubtedly leaving an outflow boundary
somewhere across northern Bangladesh. The jet streak that the models have been advertising for a week now
is approaching western India and is not quite close enough to impact Bengal today. However, adequate mid to
high level flow is in place for severe storms to develop. Unfortunately Dhaka is the only surface observation
available for the last 3 days in Bangladesh and this makes forecasting very difficult. Hopefully the MODIS
polar orbitor will make a close pass early this afternoon.
With 500 and 300mb temps around -13C, -40C across Bangladesh, the surface based lifted index at Dhaka
was -14(500) and -18(300) at 11 am local time. Needless to say, explosive instability was in place. The main
question is whether the low level shear will be adequate for violent tornadoes. The high level flow was favorable
with 75 to 90kt flow over Calcutta.
Discussion: updated 0500 UTC March 30 2006
The Bengal severe weather season may begin by April 2. I recently performed a composite reanalysis of 62
Bengal tornado cases. The synoptic situation for this coming April 2-5 is strikingly similar to this reanalysis.
Surface pressures lower across north India over the next few days. This pressure trough will deepen up to
850mb and allow for deep low level moisture to surge north into central and eastern Bangladesh.
A jet streak will approach by the April 4 and 5 time period. The ECMWF shows 850mb dewpoints
rising to around 16C with the nose of the high level jet impinging on Bengal. This is a great setup for severe
and possibly tornadic storms.
My composite reanalysis for 62 Bengal tornado cases can be found here. Note that tornadoes tend to
occur when the exit region of the high level jet is over Bengal.
GFS 114hr 500mb hgt and sfc wind from 18 UTC March 29 and valid at 12 UTC April 03 2006
ECMWF day 5 200mb and 500mb from 12 UTC March 29 and valid at 12 UTC April 03 2006
ECMWF day 7 200mb and 500mb from 12 UTC March 29 and valid at 12 UTC April 05 2006
The climatological tornado peak
is April 10-14. There is a sharp decline
in violent tornadoes after April 19. There have
been a few notable tornadoes in May. However, 2 of the most violent tornadoes on record occurred outside of the peak
period on April 26 and May 13, with 1300 and 700 fatalities respectively. The April 26th tornado path was 8 miles long
but up to a mile wide. Interestingly, the violent tornado on March 20, 2005 that killed 65 people was very early. Very
few violent tornadoes have occurred so early in the spring. The exceptions were March 19, 1961 when over 200
people were killed by a single tornado and March 13, 1953 when over 20 were killed. Only 2 violent tornadoes have
occurred after May 13.
Several factors lead to a very short but active severe weather season across Bengal.North and central India heats up and dries out in late March or early April. A deep, dry mixed
Severe storms or tornado hits Bangladesh killing over 20
people have been killed in a tornado or severe
May 17, 2005.
Bangladeshi picking up hail stones on April 25, 2005. This picture appeared in the "Daily Sangram".
Tornado hits northern Bangladesh killing 65
killed at least 65 people in northern Bangladesh on Sunday March 20,
This tornado hit Sadullahpur and Sudarganj
upazilas of Gaibandha and Mithapukur upazila of Rangpur. I am currently preparing a case study with surface and upper air charts.
On March 18, before leaving
town on a 2 day trip,
I issued a slight risk for March 19 and the first moderate risk of the
for March 20. Unfortunately, I apparently overwrote this file by mistake since I cannot find the March 20 forecast showing the
High winds and lightning killed 7 people in scattered locations across Bangladesh on March 30, 2005.
winds and lightning kill
Storms developed on March 23,
2005 in a tornado
watch. At least 16
people were killed across Bangladesh. The deaths
scattered in nature and were the result of strong straight line winds and lightning. Lightning killed 4 people working in a field.
An outflow boundary can be seen on the 06 UTC Mar 23 surface map. Surface dewpoints south of this boundary were in the
mid to upper 70s(24 to 25C) and surface based lifted indices ranged from -9 to -12 along and south of this boundary. Some of
these deaths may have been from storms on March 22.
A jet streak was approaching
Bengal as seen from
the UKMET 250mb initialization.
chart at 12 UTC March 23
showed a shortwave trough over western India. I analyzed this map despite the very poor data quality over India, and the paucity
of upstream data. The large view and small view 12UTC March 23 UKMET initialization 500mb maps are also available.
8 people were killed by lightning
in 4 separate cases in India over the past few days(March 19-23, 2005).
A late evening thunderstorm on Marh 19, 2005 killed a couple on the western end of the Khasi Hills in the Meghalaya state of India.
soundings from Dhaka--good
job BMD(Bangladesh Meteorological Department). These are
high quality soundings(especially the T/Td data)--a dramatic improvement from years past. These are from April 2004.
A tornado hit in northern Bangladesh on April 14, 2004, killing 75 people.
Click here for details about the tornado in far eastern Bangladesh on May 4, 2003.