Friday, December 16, 2016

Weather It Is (Change In The Forecast)

Good Afternoon:

There have been some strong, localized storms in the coastal areas, and rain from central Israel (Tel-Aviv) and northward will persist into Shabbat.

Otherwise, model forecast have swung back a bit towards winter, after being strongly committed to winter at the beginning of the coming week, only to recently build a ridge of higher pressure in the eastern Mediterranean instead.  Now, however, the European model and subsequently the GFS (and its ensembles) are indicating that winter (with heavy rain) will return on Sunday, and then Monday brings a good chance of rain, and even a 15% chance of snow.

What is a 15% chance of snow?  Why is he telling us this?  Strictly speaking, about 3 of the 20 (15%) of the ensemble members show the possibility of the middle and upper atmosphere supporting snow in the higher elevations on Monday. However, all the forecasts show temperatures near or below freezing in the lower atmosphere. Moreover, the strength of the building trough in the eastern Mediterranean is still uncertain, as there is still some divergence in the forecasts, and the trend is towards colder weather.

It depends in part on how the low over Spain develops, and where it moves, and more recent forecasts show it relatively weaker and further west, which means it should interfere less with the building of the trough in our area.

If all this sounds a bit like hand waving, it is -- because the global forecasts lack the information and resolution to forecast specifics more than 3 or 4 days in advance.  They are usually good (but not so good recently) at forecasting trends and general outlooks, but we need more information than this to forecast snow here because out temperatures during snowfall events are so close to freezing.

That's why we don't run our high resolution models more than a few days.  However, keep in mind that within about three days, our high resolution forecasts usually have good enough information from the global models and the grid resolution to be pretty accurate, which is reflected in the comments we receive from viewers of the site (thank you).

Moreover, with our lightning network in place, we can now run rapid updates of our forecasts that provide high short-term accuracy to predicting severe storms.

Shabbat Shalom,

Barry Lynn

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