Cu arcus

In this panoramic photo, the line of bad weather before an approaching cold front had been announced by a weak gust front on and ahead of the photographed line of Cumulus congestus with the second thumbnail showing a number of Cumulus congestus tops just before the clouds merged together to take a horizontal roll appearance (supplementary feature arcus). A Precipitation shaft (supplementary feature precipitatio) could be seen in the background. A single photo shot of the cumulus cloud on the first thumbnail taken few minutes earlier, clearly show both the congestus species and background showers. One could notice what looks like a cloud column protruding from the cumulus base when viewed against the Paola church in the background. If this was truly the case, the first thumbnail cumulus would have also acquired the very rare supplementary feature tuba. Underneath the passage of the arc cloud, the wind increased substantially from just a light breeze (Force 2) to slightly more than 40kmh before decreasing again. Some sparse and well-separated ragged shreds of the accessory cloud pannus have formed in the moistened layer beneath the precipitation shaft permitting the pannus to be identified as Cumulus fractus of wet weather.

The third thumbnail is the weather sounding taken at 1300hrs CET (some two hours later) showing a marginally unstable atmosphere conducive for cumuliform cloud formations along with moist mid-level airmass hence the overcast mid-level layer above the cumulus clouds. The visible satellite image on the fourth thumbnail taken at 1000hrs local time shows the cloud situation at the exact time when the photos were taken allowing a rare like with like comparison and analysis. Looking towards the Libyan Sea, many thin cloud lines could be noticed signifying a common forcing mechanism leading to the formation of cumulus radiatus clouds or possibly other arcus similar to the one photographed. This satellite image also corresponds perfectly with the surface pressure chart analysis on the fifth thumbnail with the cold front that was still yet to arrive in the early afternoon producing heavy thundery showers. Early night saw further local showers as the centre of the low moved southeastwards towards Malta whilst Gozo was left relatively unscathed. The sixth thumbnail shows the rain radar image highlighting the approach of a line of moderate rain showers from the photographed cumulus congestus arcus.

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