Monday, January 2, 2017

Weather It Is (Winter Storm Watch)

Good Evening:

Ynet is reporting that December was one of the coldest and wettest in many years.,7340,L-4901825,00.html

This is good news.

We've been writing for the last few weeks about the waviness in the atmospheric circulation, and how changes to the very large scale from November to December provide an extra reason to "expect" snow this year.

The problem with expecting snow is that snowstorm happen in Israel once or twice a year even when global circulation patterns or not on average favorable, and sometimes not at all.  Folks report that the winter of 1991/92 actually brought an unusually high number of snow storms, but this was followed by a period of time in which the general knowledge was that it rarely snowed in Jerusalem.

Yet, anyone born since 2011 would have a different opinion, and remember snow in more years than less, and even snow twice a year in some.

Theoretically, if the global ensemble shows a snow storm 30% of the time (where time here is the period of one week), it should snow at least one of those times during a month.  Up to now, I have been wondering if the ensemble is a bit progressive (over-predicting the possibility of extreme cold/snow).  We've seen the possibility of snow appear on the week plus forecast and then disappear as the future blends into the present.

However, the storm on the horizon (for early next week) may just restore our faith in the GEFS (if not your weather forecaster). Perhaps, even more encouraging is the agreement between the EURO and GFS deterministic models, and their ensemble for a negatively tilted trough to move in (early next week).  When troughs are oriented NW to SE, it means that the circulation around the trough will encourage divergence aloft and the spin up of a surface low pressure (bringing strong vertical motion and plenty of moisture).

In the meantime, we'll continue to have chilly weather and light rain from time to time through Wednesday. before a bit of a warm up before the next storm.

Stay tuned.

Barry Lynn

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