Weather: Could It Be Snow?

January 16, 2018

Illustration (Image credit: Wix)

 

You've probably heard: the weather indicators are pointing towards rainy and unusually cold weather. Yet, our overall weather pattern hasn't changed much. We're still expecting a series of storms to move across the eastern Mediterranean this week.

 

After issuing a "Winter Storm Watch" for Thursday night and Friday morning, the forecasts from the Global Ensemble Forecast System (GEFS) trended a bit warmer. There were still some forecasts with unusually cold temperatures, but the majority are pointing towards "just" a rain event.  This is discouraging if you're a snow-liking person.  

I know where my wife stands on this matter, because she was going around telling people that I said that it wouldn't snow. What I really said was that looking at the weather maps Tuesday morning made me less optimistic, but not completely pessimistic. Well, "a man hears what he wants to hear and disregards the rest..." (as so aptly sung in "The Boxer" by Simon and Garfunkel).

 

However, Tuesday’s forecasts (0z (00:00 UTC)) were again pointing towards a cold event.  Looking at the GEFS mean weather forecast field maps, one notes the arrival of unusually cold air Thursday night into Friday morning. In terms of the potential for snow accumulation, this will be helped out by very cold temperatures at 700 mb in the presence of strong vertical velocities. The ideal temperature for "growing snowflakes" (interlocking dendrites) is between -12 and -18 C; at the moment 40% of the forecasts indicate a drier, i.e. more likely to accumulate, snow after the rain transitions to snow Thursday night (probably after at least some have gone to bed).

 

Current forecast puts the probability of snow at even low (or lower elevations) at just 10%. Still, the European Centre for Medium Range Weather Forecast (ECMWF) at 500 mb is colder than the GEFS, so this may not be the last word on this subject.

 

In the meantime, Wednesday should bring more rain and Thursday's storm should bring even heavier precipitation, strong gale-force winds, and a chill just about everywhere. The temperatures should warm up on Shabbat and Monday, but the next storm should also bring chilly weather (with another chance for snow) mid-next week. In terms of actual snow amounts, the reader should check here on Thursday morning for an estimate by location.

 

Jerusalem forecast (click here for updated national forecasts):

Image credit: The Jerusalem Herald

 

Dr. Lynn is a lecturer at The Hebrew University of Jerusalem, Earth Sciences Department.  He is also CEO of Weather It Is, LTD, a company that specializes in reducing weather risk.

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בס"ד

...הָרִימִי בַכֹּחַ קוֹלֵךְ מְבַשֶּׂרֶת יְרוּשָׁלִָם הָרִימִי אַל תִּירָאִי אִמְרִי לְעָרֵי יְהוּדָה הִנֵּה אֱלֹקֵיכֶם! (ישעיה  מ:ט)

...Raise your voice with strength, herald of Jerusalem; raise it, do not be afraid; say to the cities of Judah, "Here is your G-d!"

(Isaiah 40:9)

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