Weather It Is (Severe Winter Storm Warning)

Good Afternoon:

Some time ago we wrote about a generally stagnant long wave weather pattern. For a while, we were on the warm side of the ridge/trough couplet.  We suggested that this type of pattern could eventually lead us to a more wintertime scenario.   This has now occurred.

The ridge has shifted to east and the trough has intensified over the eastern Mediterranean.  The result is that an intense storm should arrive here Tuesday afternoon. The storm will enter with gale force or higher winds and a sharp plunge in temperatures that will bring us below 0 at 850 mb (1500 m above the surface) by late Tuesday night.  These should sustained winds speeds of 70 km along the coast and Hermon/Golan, and 60 km/h in the areas of Sefad and Jerusalem from afternoon Tuesday into Tuesday night.  Gusts will approach 100 km/h in some  locations, especially along the coast. Strong (or gale force) winds will occur on Wednesday.

With the heavy expected precipitation late Tuesday afternoon, there is the potential to "flash-freeze" the ground in many areas of the country, including the central mountains, Galilee peaks (including Sefad) and, of course, the Golan, producing a quick snow/ice accumulation.  Initially (late Tuesday afternoon), this would be mostly large ice particles. The real snow, if it comes to the center/Safed, would have to wait until Wednesday afternoon (see below). The Hermon, however,  should steadily accumulate snow from late Tuesday into Shabbat.

Were the storm to arrive more directly from the north, it would be obvious that there is a potential for a large accumulating snow in many locations.  However, we all know that even when there is a synoptic (general picture) potential for a large accumulating snow, surface temperatures can still be a bit too warm in the not quite so high areas -- like Jerusalem.

We'll have to watch this system closely and we'll make use of our highest resolution data one to two days before to get a better idea about the potential for snow accumulation.

Regarding potential snow accumulation: temperatures at 700 mb will be marginally cold enough for good snow growth, while the very cold 500 mb temperatures will help support the development of convective snow, which is what is needed for snow accumulation under these circumstances.

The forecast suggests that it will remain quite cold into Shabbat, with periods of precipitation throughout.  The best chance for an accumulating snow in the normally snowier areas of Jerusalem and Sefad is Wednesday afternoon into Thursday afternoon, although convective periods of wet snow could continue into Shabbat.  The fly in the ointment: the sea surface temperatures will eventually warm the lower atmosphere unless another shot of cold air enters the system late Thursday.  It's possible, but not likely.

What is also possible is the potential for another storm early next week, where the cold air will arrive more directly from the north as the ridge over central Europe re-intensifies and helps set up a redevelopment of the trough in the eastern Mediterranean.

Between the wind, heavy rain/lightning, and possible snow, this is potentially an extremely dangerous winter storm.

Barry Lynn