When considering an ascent of Kilimanjaro we frequently receive enquiries about what climbers should expect in terms of temperatures and precipitation. While this information is of course useful, it tells only a very small part of the story in terms of informing a climber how they should prepare.
The following widget advises current temperatures at Kilimanjaro's assault launch camps (though please bear in mind that the large characters denoting current temperature represent the temperature at the airport, not on the mountain!).
So while these are of interest, we wish to caution strongly against the notion that climbers be overly reassured by these figures or that they may conclude that since these temperatures look much friendlier than say, a Canadian winter, or a skiing holiday on piste, as these temperatures do not offer an effective equivalent skin extremities temperature once one has factored-in the highly significant considerations associated with the body's response to altitude. Please read the below explanation for further discussion of this.
The most underestimated factor that is responsible for how a climber copes with Kilimanjaro's weather, is altitude. Until one has experienced cold at altitude, and without asking a biologist to assist us with a complex description of how the body responds to oxygen-starved environments, it is difficult convincingly to communicate the magnitude of the effect of altitude on how cold one actually feels. Nonetheless, we will attempt to offer a very simplistic explanation.
Most readers will already understand very well that at altitude the proportional composition of the air is pretty much identical to that at sea level, with oxygen making up a little under 20% of all inspired air. However, as one ascends there is effectively a smaller column of air pressing down upon the climber, between the outer reaches of the earth's atmosphere and the climber's location. As the weight of the air above the climber reduces with the increase in altitude, the force that binds air molecules together is correspondingly lessened, so the air becomes less rich, less dense. Or in common terms, we say that the air pressure becomes lower.
Depending on where one lives, we can describe normal sea level air pressure as being 1 atmosphere, or 1,000 mbar. By the time one reaches the elevation of Kilimanjaro's summit (5,895m) the air pressure will usually have dropped to around 480 - 520 mbar, or around half an atmosphere. This of course means that the density of the air being inspired on Kilimanjaro's summit is roughly half that at sea level, and therefore the number of oxygen molecules that are inspired in each breath is also around half.
Unless the breathing rate is significantly increased then, the body is trying to work with too little supplied fuel. (As an aside, it may be of interest to climbers to know that Diamox [acetazolamide] achieves this increased respiration rate synthetically by acidifying the blood, thereby effectively asking the chemoreceptors in the person's neck to acknowledge that a message should be sent to the hypothalamus to tell the autonomic respiratory system to breath more frequently so as to flush out excessive accumulated CO2 [in order to achieve the central objective of inspiring more O2].
Climbers should also bear in mind, however, that where a climber understands what is required, it is not actually necessary to artificially induce this increased respiration rate, as the climber can themselves voluntarily increase their breathing rate through practised [non-autonomic] breath control. Obviously this is not possible during sleep, however, provided oxygen debt is not experienced during daytime exposure to the day's highest elevation, hypoxia need not be expected during depressed respiration at sleep).
Thermoregulation of the body in mammals is of course very resource-intensive, wherever ambient temperatures differ significantly from temperate zones. In cold areas then, the body requires a good supply of oxygen in order to generate heat in the skin (which is obviously the largest organ in the human body), where the reduced intensity of muscle activity (necessitated by a significantly diminished fuel / oxygen supply) becomes inadequate to produce the requisite heat by-product that the body can normally use to maintain necessary skin temperature. So the problem arises in that we are asking our bodies to make a difficult decision between continuing to provide vital organs (such as the brain, which is very greedy for oxygen) with fuel, and at the same time requiring that the body expend much of this valuable and sparse supply on raising skin temperatures.
Predictably, the body's response to these demands are principally two-fold: i) substantial vasoconstriction of the small blood vessels serving the skin, with the effect being most pronounced at the extremities, namely in the hands and feet, and ii) it reduces supply to processes like digestion and higher brain function, with a corresponding reduction in IQ and lower resultant fuel demands. (We have heard difficult-to-prove assertions by alpinists that without a supplemental oxygen supply, on Everest's summit and the reduced mental function of an adult of average intelligence is roughly equivalent to that of an average 6-year old, making complex decisions almost impossible.
Climbers should please understand then, that while the minus 8 degrees Centigrade that typically can be expected at the summit may not sound very daunting, when combined with the effects of low oxygen and windchill, the level of care with which climbers should plan their clothing strategy, is a matter of very great importance that we are very happy to advise with via email correspondence.
Broadly speaking, while we are happy to arrange climbs on Kilimanjaro on any given day of the air, most climbers tend to avoid April, May and November as these represent the greater part of the two annual rainy seasons. Climbing during rainy months offers advantages in terms of lower crowds and a more beautiful summit that is often enveloped in snow, however, lower elevations are more often overcast with photographic opportunities sometimes being compromised, and a greater likelihood of being rained on.