Sunday, September 12, 2010

MONSOON WITHDRAWAL... how do we know?

this is the time of year when you'll hear conflicting information about the status of the monsoon. of course everyone has an opinion (including the weathergeek), and everybody thinks they're right!

BUT... the india meteorological department has a set of criteria that determines the official withdrawal of the monsoon from the indian subcontinent.  here are the three conditions:
1- NO RAIN for 5 consecutive days in any given region
2- the establishment of an anti-cyclone (high pressure area) in the lower part of the atmosphere
3- reduction in moisture content of the prevailing airmass, as infered by water vapor satellite imagery

some of this may sound like meteorological mumbo-jumbo, but basically it means this: the daily rainfall must stop, and the humidity/moisture in the air must drop.  the FOG is really the tell-tale sign of the monsoon's presence.  also... i think i mentioned several days ago that one of the practical signs of the end of the monsoon season is the "yellowing" of the ferns and mosses growing on tree trunks.  i have noticed that starting to happen in the last 2-3 days.

some perspective... although the historical/climatological average date of monsoon withdrawal in the dharamsala area is on or near 15 september, it has actually occurred much later than that during each of the past 6 years.
-2005... 28 sept
-2006... 25 sept
-2007... 1 oct
-2008... 28 sept
-2009... 27 sept
-2010... 27 sept (*added 3.sep.11)

so... stay tuned as we make our way through september, the most unpredictable month of the year!