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ekspeditionsdeltager Bob Oglesby
The Wacky Weather on Mustagh Ata July 14-19 2004: An Analysis
As most of you know, we suffered a prolonged, 6 day snowstorm on Mustagh
Ata from July 14-19, followed by more bad weather July 21-23. This
was not a small scale event; northern Pakistan and much of western
China suffered from the same storm.
I’ll start with a summary of my personal observations. On Mustgah,
I first noticed a change in the weather the morning of Wednesday July
14 at base camp, with low stratus clouds across the Pamir plateau,
and fairly warm (for 14,500 ft) relatively calm conditions. More ominously,
the flow seemed to be from the east or southeast, rather than the southwest
to northwest as in previous days. During that day, conditions were
not too bad; I hiked up to Camp 1 in the afternoon under partly sunny
skies. But that night in Camp 1 it snowed heavily all night (I repeatedly
had to shake snow off the roof of the tent). Temperatures were quite
mild for that altitude (17,600 ft) and there was almost no wind – just
the heavy snow. The next morning (the 15th) the snow tapered off and
the sun peeked through the clouds occasionally, though it remained
calm and mild with a southeast flow. About 2 pm, it became overcast
and began to snow very heavily again, with essentially whiteout conditions.
The remainder of the Mountain Madness team struggled to Camp 1 under
these conditions. Later that night the snow tapered off again, continuing
a pattern of approximately 7-8 hours of heavy snow followed by improving
conditions for 7-8 hours, then snow again, etc, a pattern that persisted
throughout the storm. The morning of the 16th it began snowing hard
again and at the advice of our Tibetan ‘sherpas’ we did
not even attempt Camp 2. It snowed once again all that afternoon and
night, with spectacular thunder and lightning, and the following morning
(the 17th) was our last shot at Camp 2 and then the summit. Even though
at that point something like 6 feet of new snow had fallen at Camp
1, we did try but only got up a few hundred vertical feet under windy
conditions with blowing snow before Awang, one of our Tibetan sherpas,
said it was too difficult, with which I agreed as I was already struggling
and falling behind. (The trail broken by Awang was largely filled in
by the wind within the 10 minutes it took me to reach it.) So we turned
back, alas giving up our summit attempt, and went back to Base Camp.
That night, even at Base Camp it snowed heavily (about a foot fell)
and the weather remained poor especially up the mountain all that
next day and the day after (the 18th and 19th). On the 20th the
weather appeared to break, with the wind finally backing around
to the north.
Too late for us, but a mass movement of other groups began to the
upper
camps. However, by the afternoon of the 21st the weather turned
bad again, with the same south-southeast flow setting up. It snowed
again
at Base Camp the night of the 21st, and the weather remained poor
the next day when we headed back to Kashgar. Kashgar is semi-desert,
and
only receives about 180 mm of rain per year, yet all night of the
22nd and the morning of the 23rd it rained steadily. It continued
to rain
up until we had to catch our flight out to Urumqi (fortunately
Kashgar only has a few flights so no delays!). We joked that Kashgar
received
half its annual rain just that day! (More likely it received 25-30
mm, i.e., about an inch). I understand that the weather did start
to improve in subsequent days, but I was already on my way home
by then.
So what happened? While on the mountain, I kept saying that it
looked like the monsoon flow had come up to us and that while
no one big
storm system plagued us, little ‘ripples’ or short waves in the
flow every few hours brought the bursts of heavy snow. Upon analyzing
the situation, it appears this is indeed exactly what happened. One
does not expect the monsoon moisture to make it as far north as the
Mustagh Ata-Kashgar region, so this was a fairly anomalous pattern.
This same bad weather also plagued the Karakorum range of northern
Pakistan (and the many climbers on K2 and G2). Kudos to the Pakistani
meteorology bureau, which unbeknownst to us at the time had predicted
the inclement weather as early as July 9th (5 days in advance!) and
issued warnings for climbers in the Karakorum for the same July 14-19
period.
Specifically, the Pakistani meteorologists noticed a jet stream
disturbance (essentially a middle-latitude storm) coming in
from Europe to the
west. The disturbance stalled and became stationary just to
the west of the Mustagh-Ata/Kashgar region. This upper air disturbance
triggered
a surface low pressure anomaly centered pretty much right over
us. This in turn induced a strong southerly flow of moist air
into our
region. Surface pressure anomaly maps for this time period
show
a high pressure anomaly further to the east over China and
Southeast Asia.
So in essence, this disturbance caused the summertime monsoonal
flow
to move considerably further west and north of its normal position.
Surface wind anomaly maps for the period show this strong southerly
flow into the Mustagh Ata region. Upper air wind and height
field maps show that this moisture flow was very deep, extending
most
of the way
through the troposphere (weather producing part of the atmosphere).
(Because of size considerations, I’m not including any graphics
with this write-up, but would be happy to send some maps to anyone
who might be interested, or show you where to download them yourselves
from the US Climate Diagnostics Center.) Of course even a strong flow
of moisture only sets the stage; something has to actually lift this
moisture to cause rain or snow. This lift was provided by little ripples,
or waves, embedded within the deep southerly flow. Lifting occurs during
the front portion of one of these waves, causing the snowfall, while
air descends in the back portion, accounting for the partial clearing
after a snow event. These waves typically travel through in about 12-18
hours, accounting for the approximately 8 hours of snow followed by
about 8 hours of improving conditions.
So that, hopefully in laymen’s terms, is what happened (remember
I am a professional meteorologist/climatologist so hopefully I’ve
kept the ‘jargon’ to a minimum). The other question on
everybody’s mind is how often does an event such as this happen,
that is, how unique was it? While still on the mountain, I heard plenty
of anecdotal evidence from people with experience in the area that
it was pretty rare – comments such as ‘the monsoon never
gets here; its blocked by K2’; ‘it never snows here in
summer for more than a day or so at a time’; ‘in all my
years around here I’ve never seen so much summertime snow’,
etc. But of course anecdotal evidence is not scientifically rigorous
(‘100’ year storms really happen about every 10 years!).
Unfortunately, this is a very remote region of the world that has been
little studied, so I was unable to find historical work from which
I could base a more quantitative determination of how frequently such
an event might occur. (If anyone knows of such a source please let
me know!) I did find one compelling, and somewhat disturbing study
by a Chinese climatologist named Hu Ruji form the Xinjiang Ecology
and Geography Institute, performed under the auspices of the Chinese
Academy of Sciences. This study found that over the past 15 years,
much of western Xinjiang (west of the Tianshan Mountains) has been
shifting from warm and arid to warm and humid. In particular, he has
found that runoff and lake levels have increased significantly over
this period, with at least one major lake reaching historic record
high levels in 2001 and 2002 (the study was published in early 2003).
He implies this may be due to ‘greenhouse-gas’-induced
global warming. If Ruji’s study holds true, it does suggest that
heavy snowfalls in the Mustgah Ata region (recall the summer of 2004
had exceptionally heavy snows even before the big storm) may become
more frequent as time goes by!
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