From: Dr. Bob Klein (drbob@troop111.org)
Date: Fri Mar 08 2002 - 05:26:20 CST
Here is my standard blurb on this, FYI:
I (and many others) have oft repeated the fact that the monsoon starts
at Philmont around mid-July, so treks in mid- to late-July and in August
tend to be wetter. I suspect a lot of folks don't understand why (that
is, what the heck are we talking about?)
To most Americans, "monsoon" implies torrential rains for months on end
in southern and southeastern Asia. In weather terms, however, monsoon
is not an phenomenon that is specific to southern and southeastern Asia,
but rather a general term, to whit: a seasonal change in the prevailing
wind currents over a region (any region). In India and the rest of
southern/southeastern Asia, the monsoon is a 3 month change where the
wind blows from the southwest. This entrains huge amounts of tropical
moisture off the Indian Ocean (one heck of a humidifier!) over the
continental land mass - and yeah, it rains buckets as a result.
At Philmont, the prevailing wind flow for about 9 months of the year is
from the northwest. This air has already been "scrubbed" of most of its
moisture in its travels over numerous mountain ranges from the Pacific
Northwest to New Mexico. So, generally drier conditions.
In early to mid-July, however, the monsoonal flow over New Mexico
changes from northwesterly to south and southwesterly. This means that
the primary moisture source becomes the Gulf of Mexico and the southern
Baja coast of Mexico - like the Indian Ocean two hot, moisture-rich
areas. So, you start seeing a dramatic increase in rain and truly
impressive afternoon thunderstorms as this tropical moisture gets
dragged over the mountain ranges throughout the desert southwest. This
is easily viewed on the Weather Channels national radar images - you can
actually see the thunderstorms in New Mexico heading south to north
across the Ranch.
Is this a hard and fast rule? Of course not. There is a constant
battle between the northwesterly flow and the monsoonal flow all year
long; the monsoonal flow is just a bit stronger for 3 months. In
August,
a particularly strong high pressure system in the desert southwest can
reverse the trend (back to northwesterly) for a week or more. In
addition, conditions in the Gulf of Mexico and off the southern Baja
coast are not always favorable for pumping up a lot of moisture -
there's plenty of times when you can see on the satellite imagery that
both of these areas are 100% cloud-free. Translation: drier weather at
Philmont for the next few days. This is why people can go to Philmont
in late July and August and report pretty dry weather conditions for
their trek, or sporadic thunderstorms that missed them. Conversely,
people that go in June and early July can have very heavy and nearly
constant rain (e.g., Wally Feurtado, the co-author of Cooper Wright's
Advisor's Guide, once had a June trek where it rained heavily nearly
every day. And on one of my mid-90's treks, it rained very heavily for
6 out of 7 days, then the next 5 days were "perfect." Go figure.)
However, I agree with all those who have stated that the weather is just
another part of Philmont. We have an expression in my Troop for all
camping outings which I think you'll appreciate: "Weather or Not." Got
lemons? - make lemonade.
- Dr. Bob
Becky Shifman wrote:
>
> So what is the rainy season at Philmont. Our crew is going out the first 2
> weeks in August, 2003. Does it rain on and off all summer? (and, yes, to
> anticipate some of the responses, of course we will be completely prepared
> for rain - just curious to know what you know).
>
> Becky
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