Saturday, December 9, 2017

Weather It Is (Ups And Downs)

Good Evening:

People are speaking to me about the weather, which is a lot better than when they only glared.  Instead of being angry (with me) they want to know what's with all the changes, and why it's stopped raining.

But, first the weather: our storm has departed and it will be warming up quite nicely as warm air flows moves in with a trough of lower pressure centered over the deserts to our southeast.  The warmth will peak on Tuesday, prior to the first night of Chanukah.

A cold front should then arrive Tuesday night from the west and temperatures should fall into Friday morning.  In contrast to yesterday's forecast, we're now getting indications of a chance of rain from Thursday through Shabbat. At the moment, it doesn't look  like a heavy rain.

Getting back to "why" it has stopped raining.  Unfortunately, the regional climate change models forecast that increased Carbon Dioxide levels should lead to more frequent, if not severe droughts in our area, with the drought more intense in northern areas.  This would be in response to a northward drift of the winter jet stream that provides us with "Cyprus Low," our main rain producers.

As you are aware, there are those who object to the idea that climate change caused by industrial gases is a serious problem or if it exists at all. For instance, the IPCC (Intergovernmental Panel on Climate Change) has relied on a range of climate forecast models to warn us of dire consequences in the decades ahead.  These models have produced a range of possible temperature increases during this century, from devastatingly hot to more temperate, with the mean of the projected changes depending on how much greenhouse gases we produce.  In reality, the global mean temperatures have increased (by a few tenths of a degree), but this is below or just within the lower boundary of the predictions.  In other words, > 95% of the global forecasts were/are hotter than our current reality.  Clearly, there are physical processes not well represented by most of the models.

On the other, there have been terrible fires in the western US, where it was terribly hot during the summer, and winter rains are late.  In contrast, it just snowed in Houston, Texas, and Atlanta Georgia just had its largest snow in years (several inches or more) -- and it is early December.

How do we explain that?  In simple terms, the increase in greenhouse gases has increased the energy "retained" by the atmosphere.  More energy in the system means that the waves that grow because of latitudinal (north to south (or south to north)) temperature differences can amplify more strongly (deeply) than without the added energy.  These waves can transport unseasonably hot weather further north then "normal," and colder air further south.  On the net the earth is warmer, but some areas can experience unseasonable heat or cold.

As for us, we're ahead of last year in terms of rainfall.  In fact, last year at this time it had barely begun to rain.  After rainfall began on the 13th of December, it rained a number of times before the end of the month. However, January was very dry, and February not particularly wet. We had about 50% of the normal seasonal rainfall.  However last year's fall was particularly dusty and warm, while this year's fall has felt more winter-like.  Based on this, I think there is hope for this year.

Happy Chanukah!

Barry Lynn

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