Posted by: senorwx | August 2, 2009

Rain in July ’09 – Not So Much

At the end of June we were substantially ahead of last year’s rainfall in San Pancho.

Now we’ve fallen a few laps behind. The yearly rain total at the end of July 2008 was nearly 20 inches (19.86 to be exact). This year’s July: 15.37. A five inch shortfall!

As for the monthly precipitation: July ’09 was 8.09 inches while July ’08 was 13.02. And there’s the nub of the rain problem. July just didn’t cut it.

But our friend Frank Smith at Grupo Ecologico (a far more astute individual than I) has ferreted out the salient part of this rainfall story. Quoting from his July newsletter:

Within the last eight days of June and the first five days of July, we received about twelve inches of rain, a large amount for so early in the season. During this time, temperatures were well below normal, sending many for the blankets. Despite the earlier heavy rains we’ve had less than 4 inches through the remaining 26 days of July. In any case, the early rains washed the river clean with enough force to open the lagoon to the sea, months earlier than normal. Thus, the July 4th river cleanup was literally a washout.

By the way, if you’re not on Frank’s mailing list and would like to know more about this outstanding group, go to his web site.

Oh, yes! What about that river? While the bed of the rio was cleaned up by nature, I’m still waiting to see some water in it. Can anyone help me? I thought that it was running by this time last year. Maybe that five-inch rain shortfall is the reason it is still dry.

We’ve all been suffering through some hot weather this July, hotter than last year. Here are the comparisons:

Average Temperature in July 2009: 82.83
Average Temperature in July 2008: 80.99

But here’s the comparison info that counts:

Average Heat Index July 2009: 91.68
Average Heat Index July 2008: 88.03

Maximum Heat Index July 2009: 108.76 (on Friday, July 31 at 16:00)
Maximum Heat Index July 2008: 103.99

August/September had the high yearly Heat Index readings for 2008. If that pattern persists (and I don’t have any idea that it might/could/would/should), we have many uncomfortable days ahead. And for health’s sake, keep an eye on the Heat Index (near the top of the Weather Station home page) if you have a heart or other severe health condition. When the Heat Index is more than 100 degrees, just chill out. Put off any strenuous, or even lightly-strenuous activity!

If you haven’t read the “Definitions” page of my web site, here’s the low-down on the Heat Index. It is an apparent temperature reading which uses temperature and the relative humidity to determine how hot the air actually feels. When humidity is low, the apparent temperature will be lower than the air temperature, since perspiration evaporates rapidly to cool the body. However, when humidity is high (i.e., the air is more saturated with water vapor) the apparent temperature feels higher than the actual air temperature, because perspiration evaporates more slowly.

The Heat Index is calculated by the weather station only when the air temperature is above 57 F or 14 C, because it’s insignificant at lower temperatures. It is also not calculated above 135 F or 52 C (which we wouldn’t want to be around for in any case).

A friend asked me this week for the scientific formula for the Heat Index. It’s about 3 lines long, something you’d rather forget from those days in physics class. But if you’d like to see the formula and play around with some temperature/humidity combinations for fun and pleasure, just go here.

If you have any doubt that the folks in PV have it warmer than we do, you’re correct. Their high Heat Index in July was 110.15!

Here’s one more interesting fact about our warm-fest in July: in the two-plus years we’ve been recording weather conditions in San Francisco, we reached our weather station high temperature: 92.3 on the 29th of July. It amuses me to see that in my ‘hometown’ of Boston, the highest recorded temperature for this year was 93.2 °F on April 29. Warmer in Boston than San Pancho. Rarely!

Of course, all of this information is available at the San Pancho Weather Station. And if you click through to the Weather Underground link to our station data, you can dig up all kinds of data we’ve stored there.

Thanks for reading and be sure to pass along our blog address to friends so they can subscribe to our observations about the San Pancho weather. Just click on the RSS links to the right on this page. And please feel free to add your comments and observations to the blog.

See you around the pool!

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