Sunday, March 27, 2016

Weather It Is (Winter Holds On, But...)

Good Afternoon:

Thursday night's late update suggested that heavy rain would fall in the center of the country, as well as south.  Yet, later updates trended the position of the low and heavy rain further south, until the forecast model correctly predicted that the rain system would mostly affect the south (as well as a good part of Jordan).

The Thursday night forecast for Shabbat's heavy rain was a forecast made 36 to 48 hours in advance.  We had mentioned that storms approaching from the south (with a tropical moisture source) are the most difficult to predict -- one reason being that there are fewer radiosondes (and other data sources) over Africa.

Still, there always seems to be a limit of useful predictability for our little country and I would say that beyond 30 hours is it (at least in terms of predicting the area of heaviest rain or snowfall).  There is not much we can do about this, except to possibly run more forecast ensemble members, but the cost of producing these forecasts is proportional to the number of forecasts made.

Even so, we predicted correctly that our temperatures today are more similar to those of winter and that such cold temperatures should persist until Wednesday.  With the cold temperatures will come a chance of rain at night and Monday morning, with the highest chances in the north. Forecast amounts are  likely to be between 10 and 25 mm, with rain possible as far south as Beer-Sheva.  The area of Jerusalem may also see > 10 mm over the storm's lifetime, but the probability is lower than in the north.

Another wave of low pressure should occur on Wednesday, but then temperatures should begin to climb, and they may climb all the way into the second week of April.

Spring may have finally sprung, with the exception of Yom HaAtmahut, which always seem to be rainy and/or chilly, no matter when it comes on the Calendar.

Barry Lynn

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