Synopsis of 2010-11 wet seasons

By the first of June an extended dry season is typically underway at the summit of Kilimanjaro, one of the most reliable features of a climate with considerable interannual variability. In a regional context, this dry season follows the "long rains" (Masika) which generally encompass much of the 3-month interval March through May. A second, shorter wet season (Vuli) happens in November-December and is somewhat more variable in magnitude and timing.

This year, neither Vuli nor Masika resulted in net accumulation, which will likely result in tremendous ablation on Kilimanjaro's horizontal glacier surfaces during the next 5-6 months. Just how little accumulation was there? Well, between 1 Nov. and 1 June (encompassing both accumulation seasons), a 30 cm net lowering of the Northern Ice Field was very consistent between the two sensors (i.e., -28 and -32 cm). For the same interval of 2009-10, the surface increased by over 60 cm.

During the brief dry interval between Vuli and Masika (usually occurring during January and/or February), ablation also predominated, except for one snowfall event detailed earlier that turned out to be the largest snowfall event of either 2010-11 wet season, and the largest since the previous May.

More humid... but no accumulation for March

During March, there was no snow accumulation on the Northern Ice Field. Telemetry indicates a couple minor snowfalls which weren't recorded by both of the ultrasonic sensors, and then an event of 5-10 cm on 18 and 19 March. Nonetheless, the average net change in surface height amounted to 0.0 cm.

Atmospheric humidity increased during the month however, so accumulation during April and May is more likely. This is the typical pattern, as the long rains (Masika) get underway with passage of the ITCZ over the region (see here, for example). February is rather dry on average, relative to the prior 3 months (NDJ), with the mean vapor pressure increasing 0.2-0.3 hPa from February into March. This year, the mean relative humidity increased by 20 percent; vapor pressure data are not yet available.

new video

Here is a new video produced by Caleb Medders at NBC Learn about glacier recession in general, including some brief thoughts on Kilimanjaro.

Snow!

A 3-day snowy interval was underway at this time last week, bringing over 50 cm of snow on Tuesday to Lava Tower camp at the 4,600m level - and ending an extended dry period. This snow required some climbers to turn back, according to Simon Mtuy at Summit Expeditions, as continuing up the mountain became too difficult. We hope to post photos of the event here shortly.

At the summit, snow began accumulating on Sunday the 13th and continued into the 16th. Telemetry indicates that the event brought somewhere between ~19 and 28cm to the glaciers. Through noon today (local time) the new snow had settled and ablated by 5-10cm, over the past ~5 days.

Hopefully this snowfall brought much-needed rainfall to northern Tanzania. Perhaps the "long rains" are beginning, a bit early?

[UPDATE 3/4:  Below are a couple images as the event was beginning. The first illustrates slight accumulation around the two stations on the first day of snowfall. The lower image is a view of Birafu Camp on the second day. The heaviest snowfall came the next day, which some guides describe as the most they can recall in ~4 years. Both images courtesy of Clavery Tungaraza]

Weather station images

Here is a link to October images of Kilimanjaro's weather stations. Penitentes were present at the time on most glacier surfaces, and these appear in the images. Depending upon their size, penitentes can make glacier travel rather difficult. On Kibo it is unusual to find them greater than about 0.5m in height, but in the dry Andes they develop to heights of several meters. Currently the glacier surface is likely to be much flatter, as ablation continued through what normally are the wet months of November and December.

Little snowfall to the Solstice

The 'short rains' typically bring snowcover to the summit crater by the Solstice, but not this December. One event during the second week resulted in ~10 cm of accumulation on the glacier. This was followed by drier weather, so quite likely the crater is now largely snowfree. Any first-hand observations from the summit during the holidays are welcome!

Timelapse: watch 129 days in 11 seconds

In early 2005 we installed a timelapse camera system near the weather station, with objectives of visually documenting the variability of weather (esp. clouds), glacier surface texture & roughness, accumulation & ablation, and crater snowcover. Images demonstrate the pronounced and typical diurnal cycle of convection on southwestern slopes, as well as interesting variability within the seasonal cycles.

A movie of 129 days worth of images is available here, spanning 8 Oct. 2009 to 14 Feb. 2010. To provide consistent lighting, these images are all from 6 PM local time, when the upper Breach Wall and the Furtwängler Glacier are illuminated. To fully appreciate the day-to-day variability of weather and snowcover depicted, try watching just one portion of the image (e.g., convection to the South, glacier in foreground).

The two images below are from the same time interval, illustrating dry conditions on a clear day, and fresh 'short rains' snowcover (respectively). Note the white ablation stake in the foreground; 42 cm was exposed in early October of 2009 (shortly prior to date of upper image), increasing a year later (8 Oct. 2010) to 120 cm.