The study deals with an intense rainstorm that hit the Middle East between 24 and 27 April 2018 and took the lives of 13 people, 10 of them on 26 April during the deadliest flash flood in Tzafit Basin (31.0^∘ N, 35.3^∘ E), the Negev Desert. The rainfall observed in the southern Negev was comparable to the long-term annual rainfall there, with intensities exceeding a 75-year return period. The timing of the storm, at the end of the rainy season when rain is relatively rare and spotty, raises the question of what the atmospheric conditions were that made this rainstorm one of the most severe late-spring storms.The synoptic background was an upper-level cut-off low that formed south of a blocking high which developed over eastern Europe. The cut-off low entered the Levant near 30^∘ N latitude, slowed its movement from ∼10 to <5 m s⁻¹ and so extended the duration of the storm over the region. The dynamic potential of the cut-off low, as estimated by its curvature vorticity, was the largest among the 12 late-spring rainstorms that occurred during the last 33 years. The lower levels were dominated by a cyclone centred over north-western Saudi Arabia, producing north-westerly winds that advected moist air from the Mediterranean inland. During the approach of the storm, the atmosphere over Israel became unstable, with instability indices reaching values favourable for thunderstorms (e.g. CAPE>1500 J kg⁻¹, LI=4 K) and the precipitable water reaching 30 mm. The latter is explained by lower-level moisture advection from the Mediterranean and an additional contribution of mid-level moist air transport entering the region from the east. Three major rain centres were active over Israel during 26 April, only one of them was orographic and the other two were triggered by instability and mesoscale cyclonic centres. The build-up of the instability is explained by a negative upper-level temperature anomaly over the region caused by a northerly flow east of a blocking high that dominated eastern Europe and ground warming during several hours under clear skies.The intensity of this storm is attributed to an amplification of a mid-latitude disturbance which produced a cut-off low with its implied high relative vorticity, low upper-level temperatures and slow progression. All these, combined with the contribution of moisture supply, led to intense moist convection that prevailed over the region for 3 successive days.

中文翻译：

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大气条件导致以色列内盖夫沙漠发生特大致命的山洪

这项研究涉及强烈的暴雨袭击了中东24和27之间2018四月花了13人，其中10人在4月26日的生命Tzafit盆地最致命的洪水期间（31.0 ^∘  N，35.3 ^∘  E），内盖夫沙漠。在内盖夫南部地区观测到的降雨可与该地区的长期年降水量相媲美，强度超过了75年的回归期。在雨季相对稀少和多雨的雨季结束时，风暴的时机提出了一个问题，即使这次暴雨成为最严重的后期暴风雨之一的大气条件。东欧形成的突破性高点以南形成的低水平截止低点。临界点低至30附近进入黎凡特^∘N 纬度将其运动从〜10减慢到<5  m s ^-1，因此延长了该地区的风暴持续时间。截止低点的动态潜力（根据其曲率涡度估算）在过去33年中发生的12次晚春暴雨中是最大的。较低的水平是由集中在沙特阿拉伯西北部的旋风主导的，产生的西北风使地中海内陆的潮湿空气平流。在暴风雨来临期间，以色列上空的大气变得不稳定，不稳定指数达到有利于雷暴的值（例如， CAPE> 1500  J kg ^-1， LI = 4 K），可沉淀的水达到30毫米。后者的解释是来自地中海的较低水平的对流平流，以及从东部进入该地区的中等水平的湿空气运输的额外贡献。4月26日，三个主要的雨中活动在以色列上空，其中只有一个是地形上的，另外两个则是由不稳定和中尺度的气旋中心触发的。不稳定的加剧是由于该区域的负高层温度异常引起的，该异常温度是由阻塞性高地以东的北风向东支配的，占主导地位的是东欧，并且在晴朗的天空下数小时内地面变暖。归因于中纬度扰动的放大，其产生了低截止值，并暗示了较高的相对涡度，较低的上层温度和缓慢的进展。所有这些，加上水分供应的贡献，导致该地区连续3天出现强烈的湿对流。