Weather It Is (Winter Storm Warning)

Good Morning:

Highlights:

Snow: Most snow should fall in Gush Etzion and the Golan. Rising temperatures should reduce snow accumulation in Jerusalem on Friday morning.

Winds: Gale force winds along the coast late Thursday afternoon into Friday.

Rain: Heavy rain inland Thursday night and Friday, leading to city flooding in the north and possibly in coastal areas, Jordan Valley, and Dead Sea Basin.

Dust: Heavy Dust from Jerusalem southward tomorrow morning.  High dust concentrations in the desert Thursday night and Friday.

The discrepancy between the US Global and European models has been resolved, and the US Global model (both deterministically and as an ensemble) came out ahead.  This might be a bit disappointing to snow lovers, who were hoping that this storm would rival the three day storm  of December 2013 (even in Jerusalem). On the other hand, if one sets his/her sights on the snow of Boston (or closer to home: Har Hermon), no one would ever be satisfied.  One can even go back to 1992 where the snow was hip high (and this from a relatively tall person).  Nevertheless, the snow is coming and it should accumulate.

The authors of this article from the Times of Israel keep repeating this statement:

Last week, forecasters predicted a heavy snowfall throughout the country, but the storm brought heavy rain, dust storms and gale force winds to most of Israel instead.

Read more: Israel braces for major winter storm | The Times of Israel http://www.timesofisrael.com/israel-braces-for-major-winter-storm/#ixzz3S42D3dGw 

But, this is simply wrong.  We repeated over and over again that last week's storm would arrive from the west.  As the storm would be resident over the sea for quite a while, the sea would warm the lower atmosphere, making it most likely that a wet snow would fall only in the highest elevations, but the Golan (where "real" snow fell"). We also pointed out that the marginal temperatures would result in a high melting rate. True, the path over the sea would bring lots of moisture, but for snow to accumulate it must remain a couple of degrees below zero in the lower atmosphere or be exceptionally cold aloft (at 500 mb).  We didn't see these conditions with this storm.

In fact, the forecast for heavy rain, exceptionally strong winds, and heavy dust concentrations was very accurate, including the prevalence of dust, not rain in the Jerusalem area.

This storm, in contrast, will arrive from a much more northerly direction and this will help to maximize the cold air available to this storm to produce snow. 

The cold air at lower levels will arrive towards evening, while the coldest air at highest levels should arrive from midnight to noon on Friday.  As the coldest air arrives aloft, the lower atmosphere will warm slightly as moisture flows in off the sea.  It's here that the forecast gets complicated. 

It will be exceptionally cold aloft from mid-night Thursday to Friday morning (in fact, the mean ensemble 500 mb temperatures are about -30 C in the Jerusalem area, with a range of -28 C to -34 C).  While a period of heavy snow even in Jerusalem is likely late night, there is the possibility that warming temperatures Friday morning will hold down further snow accumulations in the Jerusalem area on Friday morning, and more rain than snow is expected in the afternoon because of continued warming of surface temperatures.  

Unless anything changes in the atmospheric pattern (i.e., there is another injection of cold air), the snow should taper to light to moderate rain in many places sometime Friday afternoon and night, and end as showers on Shabbat.  

In most place, snow should begin to fall in the late afternoon or evening, depending on elevation. Here are the expected snowfall amounts from the 4 km forecast through 8 IST Friday morning. These numbers are conservative numbers, as they arrive via our 4 km forecast.

Hermon: 50 cm
Golan: 25 cm
Gush Etzion: 15 to 25 cm
Jerusalem: 5-10 cm
Bet-El/Har Bracha: 10-15 cm
Sefad: 5 to 15 cm.

Otherwise: 

Gale force wind expected late Thursday afternoon along the coast into Friday morning. Strong winds elsewhere.

Precipitation amounts: 25 to 50 mm along the coast, 50 to 100 mm inland.

Flood Potential in many locations from Thursday night onwards, including the Jordan and Dead Sea Valleys.

High dust concentrations from he southern Jerusalem area southwards from Thursday morning, with high dust concentrations sinking southward to the desert areas during the storm

Barry Lynn