Convective Outlooks
March-May 2004
Jonathan
D. Finch
Links
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Bengal
Tornadoes--background information
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 convective
initiation
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 issue tornado watch
boxes just before events
unfold.
Day 1 April
14 : moderate
risk of high-end severe storms
Day 2 April
15: moderate risk of high-end
severe storms
Discussion
for day 1: 0100 UTC April 14 (valid 05 UTC April 14 to
21 UTC April 14)
Storm clusters will continue to develop night
and day across the Assam State of India as well as over the Khasi Hills
around
Cherripunji, leaving an outflow boundary across
north central and northeast Bangladesh. Strong mid-upper level flow will
continue to be diverted around the Tibetan plateau,
with 60kts at 500mb and 40-50kts at 700mb. 30-40kt south-southwesterly
low-level jet will continue across eastern Bangladesh,
with the deeper moisture confined along and east of the 90th meridian
--central and eastern Bangladesh. The edge of
the strong capping inversion will also remain across northeast Bangladesh.
Of
course, with surface dewpoints from 75-80F, surface
based CAPE will remain very high. Any storms that develop this afternoon
and evening will produce extremely large hail
and possiblly damaging tornadoes. Other severe storms will be possible
along
the sea breeze front in coastal East India with
large hail and primary threat. Isolated storms are also possible, but not
likely,
along the surface dryline where the capping inversion
will be very strong. But any storms that develop along the dryline could
be tornadic.
April
9 - a strong storm cluster moved southeast across central and
southern Bangladesh Friday night, killing 6 people.
April
13 - severe storms injure 6 people tuesday evening
The best internet site for quality model information
for Bengal is Plymouth
State Weather Center. The most valuable
model fields include 500mb height/winds/vorticity,
300mb winds and sea level pressure/precip. The positioning of the
high-level jet is one of the most important predictors
of severe storms in Bengal. These fields are available for the
UKMET-global, ECMWF-global, AVN-nh, AVN-global,
and MRF-nh. Of course the avn and mrf are now called the GFS.
Meteorologist Rob Stokes
has just arrived in the Bengal region today(April 8). He will be laying
the groundwork for
future, pioneering storm
chasing! He knows that the surface visibility is terrible there(due
in part to millions of people
cooking outside), and is
well aware of the many challenges. He is considering airborne chasing to
get above the wretched
haze layer. Just
found out that Rob is not in Bangladesh yet. He is still in Thailand trying
to get a visa. Perhaps he will
be in Bangladesh by Tuesday.
Unfortunately the upper air data over the Indian
subcontinent is very poor quality. The best quality site is Calcutta. Here
is
an example of how bad
the data is. This often makes analysis very dificult.