Monday, January 25, 2016

Weather It Is (Winter Storm Warning)

Good Morning:

Winter Storm Warning for Extreme Cold and Possible Snow/Ice.

We've had reports of a light accumulation of snow in the higher hills of Gush Etzion, including Kiryat Arba.  However, here in Efrat, this was the extent of our snow (picture below).

The difficulty is forecasting snow amounts pertains to the forecast temperatures being just above freezing throughout the day (right now, it is 1 C here in Efrat).  This means that snow must fall faster than it melts, and this is very hard for surface snow algorithms to predict. Our current forecast shows 17 cm in Gush Etzion by tomorrow morning, but only a couple of centimetres in Jerusalem.

However, there are complicating factors which are making this snow prediction very hard.

First, temperatures at 850 and 700 mb will fall by a degree today (to about -2 C and -12 C), which is more favourable for snow, and temperatures will fall by another degree at 850 mb tonight. More importantly temperatures will fall by almost 5 C at 500 mb, reaching ideal temperatures for snow in the higher elevations, including Jerusalem, and stay this way until almost Wednesday Evening. The decrease in temperatures at 500 mb also opens the door for convective snow with lightning, as the onset of the upper level trough will bring divergence aloft and deep formation of clouds.

Second, the highest amount of convective-like precipitation is predicted Tuesday morning, but temperatures with the influx of moisture will rise a bit at 850 mb.

Third, there seems to be an issue with phasing of the northern and southern Jet streams (at pointed out as well by in interested reader).  Hence, even though it will be intensely cold from Tuesday afternoon, in Wednesday afternoon there may be a lack of significant moisture, reducing potential snow amounts.

Yet, our forecasts show temperatures in the late afternoon falling to the freezing mark, and during snow episodes possibly a two to three degrees below.

In summary, accumulating snow is most likely in the area of Gush Etzion and surrounding higher elevations around Jerusalem, and roads will definitely become icy late afternoon/evening (with possible snow on roads in heavier snow bursts this afternoon).  Snow in most likely in Jerusalem tonight and tomorrow morning, but our forecasts don't show a heavy accumulation there.

Keep in mind, that the temperatures will be extremely cold and that the synoptic conditions are set for a major snow storm -- given the caveats I mentioned.

The Israeli Meteorological Service is quite favourable for snow, even in Jerusalem.  For snow lovers around, perhaps they'll be correct.

On my end, I've put on my boots, red wool hat, and I  even rebooted my computer.  Will it be enough, I don't know.  Sometimes, the meteorologist is not necessarily better off than you who reads this column.

Barry Lynn

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.