Flash flood and related hazards occurred over the Haor (wetland) areas of northeast Bangladesh during 17–18 April 2010. Prediction of this sudden incident is challenging when it happened on the high terrain of Meghalaya Plateau and adjoining Bangladesh. Flash flood event occurred when convective cells assembled into a mesoscale convective system (MCS) over the steep edge of the Plateau. The MCS obtained its extreme point after getting moisture support from the southerly flow of the Bay of Bengal (BoB). This study investigated the synoptic flow patterns and large-scale characteristics of the flash flood-producing storm and its associated tropospheric conditions in northeast Bangladesh using the Weather Research and Forecasting (WRF) model. The model used a 3-nested domain with the horizontal resolution of 27 km, 9 km, and 3 km, respectively. The study revealed that the model underestimated the strength of the flash flood in general in respect of rainfall. The 48-h simulated rainfall was about 152 mm for outer domain-1, about 195 mm for inner domain-2 and about 209 mm for the innermost domain-3 whereas actual rainfall was 223 mm as recorded by Bangladesh Meteorological Department (BMD). The southerly wind was strong at 950 hPa and the westerly wind prevailed at 500 hPa level. The model simulated results show that cloud water mixing ratio was 1.8 mg m−3 and extended vertically up to 17 km. Ice water mixing ratio was 200 mg m−3 and found in between 12 and 20 km, indicating the formation of ice in the upper troposphere. The maximum values of x, y, and z-wind components over Cherrapunji were − 11 ms−1, − 21 ms−1 and − 2.8 ms−1, respectively which indicated the strengthening of the convective system to produce flash flood.

中文翻译：

---

孟加拉东北部山洪暴发的天气流型和大尺度特征

2010 年 4 月 17 日至 18 日，孟加拉国东北部的 Haor（湿地）地区发生了山洪暴发和相关灾害。当它发生在梅加拉亚高原和毗邻孟加拉国的高地时，预测这一突发事件具有挑战性。当对流单元在高原陡峭边缘聚集成中尺度对流系统 (MCS) 时，就会发生山洪暴发事件。MCS 在得到孟加拉湾 (BoB) 向南气流的水分支持后获得了极值点。本研究使用天气研究和预报 (WRF) 模型调查了孟加拉国东北部引发山洪暴发的风暴及其相关对流层条件的天气流动模式和大尺度特征。该模型使用水平分辨率分别为 27 公里、9 公里和 3 公里的 3 嵌套域。研究表明，该模型总体上低估了山洪暴发在降雨方面的强度。外域 1 的 48 小时模拟降雨量约为 152 毫米，内域 2 约为 195 毫米，最内域 3 约为 209 毫米，而孟加拉国气象部门 (BMD) 记录的实际降雨量为 223 毫米。950 hPa 偏南风强，500 hPa 盛行西风。模型模拟结果表明，云水混合比为1.8 mg m−3，垂直延伸达17 km。冰水混合比为 200 mg m-3，发现在 12 至 20 公里之间，表明对流层上部有冰形成。Cherrapunji 上 x、y 和 z 风分量的最大值为 − 11 ms−1、− 21 ms−1 和 − 2.8 ms−1，