Snow in the Sahara Desert – Unbelievable But True!

11 01 2018

Dale C. S. Destin |

sahara-desert-map

A few days ago, snow fell over parts of the Sahara Desert. To many this was unbelievable, especially in this era of fake news and alternative truth. However, it really snowed in the Sahara Desert, and not for the first time. Precipitation (rain, snow, hail, etc.) in deserts are rare but certainly not unheard of.

Algeria - dark green

Location of Algeria – dark green

 

Snow covered dumes in the Sahara Desert. Photo by Geoff

Snow in the Sahara Desert near the town of Ain Sefra, Algeria – 07 Jan 2018. Photo by Geoff Robinson 

It is understandable the disbelieve one would have about the news of snow taking place in the Sahara Desert. After all, it is “only” the hottest desert in the world – consisting of some of the hottest places on Earth. The mean temperature is around 29 °C (84 °F) but can reach as high as 50 °C (122 °F).

What is not well-known is the fact that very cold temperatures do occur in the Sahara Desert. Temperatures, particularly during winter can fall below freezing (below 0 °C or below 32 °F). So, temperatures do become conducive for snow in the Sahara, at times. However, temperature is not sufficient for snow – moisture is needed.

Contrary to popular belief, precipitation does take place in deserts, including the Sahara. Not a lot takes place but they do get precipitation. There is no universal definition for a desert but a good working one is an area receiving less than 250 mm (10 in) of rainfall annually.

In the case of the Sahara, the annual rainfall is less than 100 mm (3.9 in). It rains from December to March and in August. The rains in August are said to be characterized by thunderstorms, which can produce flash floods. And of course, snow falls at times during the winter months, as was the case a few days ago.

It snowed in the same location last year; however, before then it had not snowed in 2012 and 1979 -nearly 40 years ago.

Sahara snow event of 2012 as reported by Algerian TV channel, Central TV

Weird precipitation events are rare for deserts but they do occur:

In January 2013, a NASA satellite observed the Taklimakan Desert, in western China, covered with snow. The Taklimakan Desert temperature range from – 20 to 38 °C (68 °F to 100 °F) and the annual average rainfall is less than 40 mm (1.60 in).

In August 2011, Stephane Guisard of the European Southern Observatory photographed snow in the Atacama Desert. The annual average rainfall is around 1 mm (0.04 in).

A dusting of snow in the Atacama Desert

A dusting of snow in the Atacama Desert. Photograph was taken by Stéphane Guisard on 1 August 2011. 

In March 2015, Flash floods took place in the Atacama Desert – the driest desert in the world and one of the driest places on Earth. The annual average rainfall is around 1 mm (0.04 in). The floods caused two deaths and left 24 persons missing.

Precipitation may be rare for the deserts of the world but far from unprecedented. No only do they get light precipitation but also solid, on occasions.

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Windy Weather to Cause More Hazardous Seas and Economic Losses

8 01 2018

Dale C. S. Destin |

Hazardous seas being caused by frequently strong winds – gusting to near gale force at times, will continue to keep most mariners in or near port over the upcoming week – causing further significant economic losses for many.

Seas around Antigua and Barbuda have been rough for most of the year, so far, and are set to remain that way or even worsen over the next seven days, at least. As usual, this type of weather is very disruptive to marine activities and have a negative economic impact, particularly on fisherfolk, those alone the fisheries value-chain and those involve in offshore pleasure cruises and adventures.

Small craft warning remains in effect for hazardous seas around Antigua and Barbuda and will likely remain in place for the rest of the week. Hence, small craft operators, especially inexperienced ones, should avoid navigating in these conditions.

Warnings are also in effect for beach-goers as high surfs are affecting beaches, producing beach erosion and dangerous swimming conditions. Beach-goers should avoid the waters, especially those on the northern and eastern side of the islands. These high surfs are likely to subside to more manageable levels by Tuesday.

High surfs can also cause strong rip currents, which can carry even the strongest swimmers out to sea, and seawater splashing onto low-lying coastal roads, causing damage. Further, high surfs can also knock spectators off exposed rocks and jetties. Breaking waves may also occasionally impact harbours making navigating the harbour channel dangerous.

The wind speed will range between 14 and 22 knots (16 to 25 mph) and at times gusting to near 30 knots (35 mph). The winds will be strongest on Tuesday and Friday and will blow from near east for most of the week.

Wind speed – valid at 6 am, Tue, Jan 9, 2018

Seas will remain hazardous with steep waves ranging between 2 and 3 metres (7 and 10 ft), occasionally reaching near 4 metres (13 ft), mainly in open waters on the eastern or windward side of the islands.

Significant wave height (ft) – valid at 6 am, Tue, Jan 9, 2018

These strong winds not only cause hazardous seas but also cause certain onshore activities to be uncomfortable, if not dangerous. Hence, certain outdoor work will be hampered, if not halted, at times; thus, reducing productivity in other sectors.

The windy conditions and hazardous seas will also be experienced by all the islands of the Eastern Caribbean along with Hispaniola and the Bahamas, particularly the Atlantic coastal waters or the eastern and northern coastal waters.

The strong winds are not due to any storm system but rather because of steep pressure gradients across the area. Recall that winds blow due to pressure differences or pressure gradients, and the greater the gradients the stronger the winds and vice versa.

Also, the strength and position of the ever-present subtropical/Atlantic high-pressure system modulate the steepness of the pressure gradient. The closer and or stronger the subtropical high, the steeper the gradient, the stronger the winds and vice versa.

The subtropical high-pressure system will be stronger than normal for much of the next week; hence, the forecast continuation of strong winds, hazardous seas, disrupted marine activities and economic losses.

Although windy, the weather will be mostly dry with only occasional brief showers likely.

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