[pct-l] katabatic, adiabatic, and other noteworthy tics

[blisterfree at isp01.net (Brett)]

>>>If you descend into the desert from the dry side (east 
>>>side in CA) of
mountains, the temperature increases at a rate faster than 
it was decreasing
as you climbed the west side. That's why the deserts to the 
east of the
Sierra are not only dry (the rainshadow effect) but so damn 
hot!<<<

Slightly OT, but www.weather.com now offers 30+ day 
forecasts. That's right - a whole month's worth, for every 
dang place in the country. Okay, so it's more like the 
farmer's almanac beyond the 10th day (or is that the 2nd?). 
In fact, after day 14, all they offer are statistical 
averages for that calendar date at that locality.

This information is utterly useless for planning purposes, 
and is not a forecast in any way. Then again, maybe they 
know that, since much of their tv programming seems aimed at 
garnering the weather geek quotient from the sum total 
viewership.

But the information is very useful for understanding how 
weather, and in particular temperature, patterns shift over 
the course of days, weeks, and seasons. In most regions of 
the country, both high and low average daily temperatures 
are now, in early February, just beginning to climb from 
their winter minima. Like the hours of daylight as we trend 
toward spring, this upward creep in temperature begins 
slowly at first, then picks up steam as the sun gains 
greater dominance over our hemisphere. Hours of daylight 
increase most rapidly toward the vernal equinox, and then 
increase more slowly until the summer solstice. Temperatures 
follow a similar pattern, but lag behind the gains in 
daylight, much the same way the ocean's temperature lags 
behind that of the air.

So everyone, on average, is currently gaining heat as well 
as light. But some areas are gaining heat much more quickly 
than others. These tend to be the regions with the greatest 
differential between winter average and summer average 
temperatures, especially where the length of time between 
these extents are the shortest.

Take a gander at Tucson, Arizona for example, my old home 
town. Currently, average daily high temps are climbing by 
about 1 degree per week. However, in a few weeks from now, 
they begin to gain 1 degree every 5 days. Then a week later, 
every 4 days. By mid April, the dry desert air, minimal 
ground cover, and strong unfiltered sunlight allows that air 
to climb 1 degree every 3 days. I'm not sure what happens 
next, as WC "calendar" doesn't progress beyond this point 
yet. However, having lived there, I believe every bit of it. 
Whereas the northeast, my current locale, hails March "in 
like a lion, out like a lamb," it seems the Sonoran desert's 
seasonal adage best applies to the month of April. "In like 
a lamb. Out like a well-done goat."

The PCT is a "mountain trail" that happens to descend into 
the desert at various places. Springtime temperature 
differentials between the two regions can be amazingly 
pronounced. A thru-hiker might prefer to hike the desert 
when it's cool, if not for all the snow still up high. Or 
hike up high without a trace of snow, if not for the 
sweltering conditions down below.

- blisterfree

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