Trough of low pressure moves over Oman
13 March 2014 00:00 UTC–16 March 23:45 UTC
Low pressure affected Oman from 13–16 March, causing six deaths, despite numerous warnings being issued by the Oman Met Office.
29 September 2022
12 March 2014
by Khalid Al-Jahwari, Mahmood Al-Khayari and Shima Al-Yazidi (DGMAN, Oman), Jan Fokke Meirink (KNMI), Rob Roebeling and Jochen Kerkmann (EUMETSAT), HansPeter Roesli (Switzerland)
In mid-March 2014 the weather of Oman was influenced by a trough of low pressure, which caused several days of unsettled weather
Rains in northern Oman started on 13 March when a first cloud band reached the UAE and the northern tip of Oman, as seen in Figure 1.
Download animation of Meteosat-10 IR10.8 images for northern Oman, 13 March 00:00 UTC–16 March 23:45 UTC
Upper image: Meteosat-10 IR10.8 image with 300 hPa absolute topography (ECMWF analysis, Credit: EUMeTrain), lower image: Meteosat-10 Dust RGB image (Credit: EUMeTrain).
In this converted PDF the IR10.8 image of 13 March, 06:00 UTC (slide 2) shows many clouds over the southern part of the Arabian Peninsula, but from this image alone one would not be able to tell from which clouds the rain is coming from.
The Natural Colour and the Dust RGBs (slides 3 and 4) help to discriminate ice from water clouds and to identify moisture boundaries (Dust RGB). But one has to look at the Day Microphysics RGB (slide 6) to better identify thick ice or water clouds that may produce rain.
Slides 9 and 10 show a comparison of the Day Microphysics RGB product with the precipitation product from the KNMI cloud products web map service.
All clouds identified as rain showers in the RGB products are also identified as rain clouds in the quantitative precipitation product.
More information on the KNMI cloud products from MSG SEVIRI is available on the KNMI web portal.
Musandam (the northern tip of Oman) continued to receive moderate to heavy rains on 14–15 March. The highest total rainfall amount recorded was 48.2mm at the observation station of Khasab.
However, there is a rain gauge operated by the ministry of water resources in Lima (circled in red in the map) which recorded 415mm of rain. This is a very large amount of rain, even exceeding the amounts of rain recorded during Tropical Cylone Phet in 2010 — hard to believe.
As there is no weather radar data available to verify the high rain values measured in that area, we calculated the accumulated rainfall from two KNMI precipitation products.
Firstly, the simple IR-based product, which is a simple product that estimates the rain-rates directly from the observed infrared brightness temperatures at the cloud top.
Secondly, the microphysical cloud properties-based precipitation product (daytime only), which uses cloud water path, cloud particle size and the height of the liquid column to retrieve rain rate, see description of the algorithm, Roebeling et al., 2012.
The results are shown in Figures 2 to 7. Both satellite products do not confirm the very high amount of rain recorded at the station of Lima, but the microphysical product gives higher values, in the order of 32mm/12 hours on 14 March (due to parallax shift the pixels with high rain are shifted a bit to the north-east).
The IR-based product shows no precipitation on the 14th for the area of Lima. This indicates that much of the rain that had fallen in Lima was from water (warm stratocumulus) clouds and not from cold, ice clouds.
On 15 March, the upper level trough caused the formation of convective cells over the Al-hajar mountains and neighbor areas in Oman, see Figure 8, and animation of IR-HRV sandwich product, the coordinates of Bahla are highlighted by the red cross. The formations were enhanced by moisture feeding from the Arabian Sea and mechanical uplifting of the Al-hajar mountains.
The most intense period was around 11:00–13:30 UTC. Meteosat-10 captured two marked convective cells: one brought heavy rain in Al-Dhahira and Al-Batina regions; the other (to the south) passed over Bahla and produced hail.
The cloud top temperatures reached 220K, as seen in the IR 10.8 images, which is not particularly low. The other parts of Oman reported light rain.
This infrared animation shows development of thunderstorms that continued during the night over the Al-sharqia region.
This image shows that Ibra recorded 58.2mm and Al-Mudhaibi 9.4.mm.
This event also resulted in the flow of Wadis in different parts along the Al-hajar mountains. The animation of Dust RGB images from 16 March, 05:00–07:00 UTC showed the post-frontal dust plume blowing over the north part of Oman.
Additional content
Animation of Meteosat-10 microphysical precipitation product, 15 March 08:00–13:00 UTC (Credit: KNMI)
Meteosat-10, Convection RGB product, 15 March 12:30 UTC
Terra MODIS image, 16 March 06:55 UTC (Credit: NASA)
References
Roebeling, R. A., E. L. A. Wolters, J. F. Meirink, H. Leijnse, 2012: Triple Collocation of Summer Precipitation Retrievals from SEVIRI over Europe with Gridded Rain Gauge and Weather Radar Data. J. Hydrometeor, 13, 1552–1566. doi: http://dx.doi.org/10.1175/JHM-D-11-089.1
