Currently, in Bangladesh, the danger level is designed and updated considering the riverine flood during the monsoon season (Jun–Sep). There is no warning or danger level to inform the community to save the Boro crops from flash floods (Mar - May) in that region. Hence, this study attempts to establish a flash flood danger level at 40 locations in the northeast region of Bangladesh based on flood frequency analysis and elevations of the river floodplains. Among the candidate distributions, the Generalized Extreme Value (GEV) distribution was found to be the best distribution for flood frequency analysis. Then, the danger level was fixed on the basis of the flooding inundation scenarios of different return periods at which the stage is at or near the floodplain level. The results showed that for most of the stations, the 2.33-year flood level coincides with the existing floodplain level. For the rest, flash flood danger levels were fixed at the 5-year return period’s flood level. The recommended flash flood danger levels were found much lower than the existing monsoon flood danger levels. For example, at Sunamganj station, the existing flood danger level is 8.25 mPWD (Public Works Datum), whereas the recommended flash flood danger level is only 6.41 mPWD. At some stations, the difference is too prominent, even more than 5 ft, which can cause severe destruction for the Boro rice cultivation during a flash flood.