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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    The purpose of this website is to forecast high-end severe storm episodes in Bangladesh and East India. High-end
    severe weather (1.75 inch or larger hail and destructive tornadoes) is usually produced by supercell thunderstorms,
    so supercell storms will be the main focus of these forecasts.

    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.




    Updated April 14, 2004 0100 UTC

    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.
          



    Recent storm news for Bangladesh and India

    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.