Weather It Is (A Storm Arrives And Then What?)

Good Evening:

Highlights:

Winter Storm Warning for the Hermon and Golan for Wednesday into Thursday.

High Wind Warning for Gale Force Winds.

Flood Risk from south-central Israel to northern Israel (with the heaviest rain occurring as one moves northward).

Winter Storm Watch for Gush Etzion and the Highest peaks around Jerusalem.

I am writing late because I spent the afternoon trying to find the last "Who" in "Whoville" who might be keeping quiet. The one who might the tip the balance in favor of those who want snow versus those who don't.  I didn't find him (or her).

Hence, there is quite a conundrum.  The forecast has changed quite substantially within the last couple of days.   Instead of extreme cold in the lower levels and relatively mild temperatures aloft, the forecast is showing "snow" cold in the lower levels and extreme cold in the upper levels. This makes it less likely that temperatures will be cold enough for accumulating snow in Jerusalem.  Snow, though, is still likely in the higher elevation of the Galilee and hills surrounding Sefad.

Moreover, there are large forecast differences between the new version of the Global Forecast System (GFS) and its old version (still in operational use).  The new GFS produces a deep, wintertime trough over the eastern Mediterranean, similar to the ECMWF and Canadian model.  So, in the discussion below, we're relying on the new GFS and our downscaled Weather Forecasting and Research (WRF) model based on it, rather than the old GFS.

The extreme cold in the upper levels is conducive to the production of "thunder-snow," which often leads to a snow accumulation when combined with cold lower atmospheric temperatures.  However, our high resolution forecast is again showing that surface temperatures will remain above freezing in a saturated surface layer.  This means -- again -- that snow will melt with the exception at the highest elevations of Gush Etzion.  Folks even in Jerusalem should see snow, especially from noon Wednesday to about midnight Wednesday night, but it maybe hard pressed to stick around.  Regardless, expect there to be elevation dependent icy conditions anytime during the height of the storm. Heavy rain and/or blowing snow could reduce visibility to only several meters.

In a previous blog I wrote that there are things we know and things we don't know. One of them was could one rely on  the Global Ensemble Forecast System (GEFS) model forecasts after the individual forecasts converged to a tightly clustered group.  In our case, we were wondering whether after the different forecast members of the ensemble converged to produce greater certainty would they as a "close-knit" group deviate from their previous forecast of extreme cold.  The answer is in, and they have deviated.  As noted, the upper levels have cooled off significantly from their previously shown values, but the lower levels have warmed up significantly.  Whether this indicates a problem with model physic and numerical integration (or simply that the distribution of possible forecasts is not wide enough) is still an unknown.

What I hope to find out after a bit of research I am engaged in now is what is the probability that a forecast that is tightly clustered will occur as previously forecast some days in advance.  This is on going research, and there is no clear answer yet. In other words, there are forecast probabilities and then there is the probability that the mean of the forecast will be within a certain range.

At the moment, no significant storms are shown for next week, which is a big change from the past several weeks.

Barry Lynn