Wednesday, May 2, 2018

Weather It Is (Hot Day for Races)

Good Afternoon:

It looks like the next several days will be quite hot, with temperatures in the upper 20s to low 30s until about next Tuesday.  The hot weather is a result of complementary weather systems.  The first is a  high pressure located over northern Africa, which is nosing its way northwards along the coast.  The hot winds are blowing from southwest around this area of high pressure. The second is actually a series of weak low pressure areas moving along the southern Mediterranean coast.   The  winds   associated with the low pressure systems are called "Sharav" or "Chamsim" (Hot) Winds"

Yet, no matter what you call them, they are hot winds.  Moreover, for those participating in various races or other sporting events, the dry heat associated with them can be dangerous. So, it may interest you to know that I received a phone call asking about the intensity of the heat for the races in Gush Etzion this Friday.  While I would like to help, one has to be careful when providing an answer to such an important question.  One can look at global model forecasts, but the grid-spacing is too large and the time intervals too coarse to provide a meaningful (or useful) answer (this is done far too often) Yet, when I mentioned that I would need a bit of time to formulate an answer (meaning to run forecast simulations at the appropriate grid size-spacing and forecast output intervals), I was told that they had to decide and that they would make due with the information they have.

Of course, this approach is not an optimal use of forecasts.  For instance, our web site shows that the temperature range during the race (e.g., 0600 to 0900 in the morning) should be between 28 and 32 Celsius.  It also shows that the Sharav will be approaching the coast after the race, which implies that the peak temperatures will be during the race.

Considering the summary of heat stress effects at this U.S National Weather Service link,, one might be concerned that temperatures would be approaching levels that could lead to heat cramps, and heat strokes. However, the forecast on our web site while providing a general idea of the weather (it will be hot) was not run a high enough grid-resolution to provide the details the race organizers need to make an informed decision. In addition, there is the issue of risk, which can only be determined by a probabilistic forecast (i.e., ensemble). The goal would be to calculate the chance that temperatures, for example, will exceed certain values during the race itself.

All of these approaches, i.e., using higher grid-resolution forecasts and making multiple (ensemble) forecasts can be done given some "heads-up" warning time, and the will to obtain the best information available.

Otherwise, we make-due" until we don't, and tragedies happen.

Stay cool,

Barry Lynn

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