Overnight on 19-20 December 2016 there were heavy snowfalls in Jordan and in Turaif city in Saudi Arabia.
10 November 2020
19 December 2016
By Ahmed Alhayek (Al-Damam, Saudi Arabia), Hilal Al-Hajri (Muscat, Oman)
Generally in the winter the northern part of Saudi Arabia is affected by a passage of upper air troughs. The areas ahead of these troughs always have the significant weather, in terms of heavy rain and snow falling, sometimes with a strong downdraft.
Due to the wind divergence at the upper level of the atmosphere, a convergence of wind in the lower atmosphere occurs. This convergence generates the uplifting mechanism considered as the main process for cloud formation and vertical extension of cloud.
In addition, the position of the jet stream also enhances the convection. Moreover, the zero level was down at approximately 800 hPa.
A combination of these condition late on 19 and early on 20 December caused snow over Turaif city. Figure 1 shows the location of the affected area.
As can be seen in the water vapour image, Figure 2, there was significant upper-level moisture in the affected area. Knowing that, the yellow dashed line is the jet stream, the green line is the deformation zone, located directly over Turaif, (N) is an area of minimum vorticity and (X) is an area of maximum vorticity. The maximum vorticity was located over the affected area.
On the Night Microphysics image (Figure 3) the number 2 indicates cold-thick high level cloud which caused the falling of snow, number 1 indicates low-level cloud over a cold surface and number 3 indicates low-level cloud over a warm surface.
By adding the surface 10m wind the story becomes clear — two different characteristic air masses (green and black arrows) converged over the affected area and formed a good convergence line (white line), as can be seen on Figure 4.
Looking at the Natural Colour RGB (Figure 5) there is no difference between the ice cloud and the snow over land. However, by looking to the animated Natural Colour RGB images (Figure 6) it is very easy to differentiate between them as the cloud is moving and the snow is fixed in its location. Moreover, the snow started to melt when the sun rose over the horizon.
Snowfall in Saudi Arabia (Arab News)
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