Wednesday, January 20, 2016

Weather It Is (A Lot Of Confusion And Some Clarity)

Good Evening:

You might be confused, or your friends might be confused, but it's not you or them I am speaking about.  I am speaking about the forecast models.

There have been some very snowy forecasts in our past -- and by past I mean just last night, or even this morning.

In the snowy forecast, a strong trough arrives early Sunday bring heavy rain and rapidly cooling temperatures -- and rain changes quickly to snow. After a slight let up, extremely cold air streams southward again and we chill down even more -- all the way until Wednesday.  This is a very snowy forecast.

In the non-snowy forecast: a strong trough arrives early Sunday, but it doesn't quite get going. The 500 mb really cold temperatures arrive before the cold air in the lower atmosphere, and then exits too soon. Then, before the second storm arrives the main area of cold air swings too far east.  The result: some wet snow, maybe, and then several days of just wet, cold, and nasty weather -- but no snow (except on the Hermon).

If one looks at just the main models, for example: the GFS, EURO, GEM, etc, one will see a snowstorm on the near horizon in some of these models, in some part of their forecast cycle, and even more than once in a row, and then no-snow at all.

Likewise, if one looks at the ensemble forecasts -- like the one late night -- one sees several days of frigid cold weather (80% chance).  However, the next ensemble run suggests an initial storm (possibly snow), and then a 50% chance of additional snowstorm.

If it makes you feel any better, there is a similar problem facing the forecasters who are forecasting the next storm on the east coast (just three days away).  The still don't know if there will be a blizzard or just some wet snow in NYC, rain on Long Island, and dusting in the cooler suburbs.

What this means is that there simply are still too many unknowns to really say much about next week's weather.  There are simply too many interactions happening in areas where there isn't enough data to properly resolve these circulation features (there may also be problems predicting them as well). If one were to average the ensembles and average the individual models, I'd put the probability at about 35% for snow in Jerusalem, and 50% in Gush Etzion and the upper Galilee.

Will it snow as early as Sunday morning?  Stay tuned.

Barry Lynn

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