WEATHER: Cold Snap Decisions

Airbus Undergoing De-Icing by Alex Pereslavtsev [GFDL 1.2] via Wikimedia

When your own daughter turns against you, you know it is time to take down your barometer. She is not the only one who asked me to end winter, reset the clock (if possible), and go forward to spring.

Based on conversations within my Israel Winter Weather group, I should mention that rainfall is much above normal this winter season, while temperatures are cumulatively below normal. The combination has made for both a chilly and wet winter — and led to rather disgruntled readers who don't remember what winters used to be like. There have been only two colder-than-normal winters since 2003-04, but this is probably the only wet one of the bunch.

Despite the chilly start to the week, temperatures should rise slowly over the next few days, but then they will start a persistent decline towards the last week of the month.

When deciding what to write next, one should be very careful with one’s words. For instance, I won't mention that 10 cm. of snow fell on March 18th, 1998 in Jerusalem or that during March 26 through 27, 1967, there were snow accumulations from the north to the northern Negev. One might also not mention that according to meteorologist Uri Batz there were 15 cm. of snow in March 1874 and 20 cm. in March 1880. Also, I wouldn't dare to mention that 10 cm. of snow fell in Jerusalem on March 16th, 1948.

I can mention that the last week of March should be a wet one with strong winds but I won't mention that the chance of snow has risen from 15% to 25% from yesterday to today. I won't mention this because climatologically speaking snow is very, very unlikely at this time of year. Instead, what is more likely is strong winds, rain, and hail.

Should I mention snow? In general, there are both good and bad decisions made everyday. Some are made out of hubris, and some are made out of greed. Others are made out of kindness. In fact, my decision to take care of a stray cat led indirectly (but it did) to my meeting my wife (who DID NOT like cats at that time).

While it seems comparatively trivial, I certainly could have decided not to mention that the forecasts are hinting at a possible late month, early Spring snow. Yet sometimes, decision making can lead to tragic circumstances.

In a much more somber example, a number of bad decisions led to the 2009 Air France Flight 447 crash; yet some of the decisions were not connected to each other. The pilots chose incorrectly not to divert around a tropical storm (like most other flights that day). Then, the radar on the plane was not tuned to the right mode, so they inadvertently entered an area of intense thunderstorms. This led to the clogging of sensors that enabled the automatic pilot to function (based on measured air-speed). Then, the junior co-pilot tried to take the plane over the area of bad weather, and both co-pilots initially ignored the warning that the plane's speed was decreasing enough to stall. In the meantime, the captain had just previously left the cabin to take a nap, and when he returned he was not able to take effective action in time to save the plane.

However, one decision made far from the airplane itself was the final touch. Airbus decided to link the "side sticks" that control the plane tilt — nose up or down. That meant that when one pilot tried to lower the nose of the plane to pick up speed, he was unaware that the other was (incorrectly) doing the opposite. A decision made well prior to the crash of this plane in the end doomed it.

Replicating a similar design flaw, another aircraft designer, Boeing, is in a lot of trouble for decisions made (both past and present) in creating a plane and system that has already led to two plane crashes — the most recent earlier this month in Ethiopia. As noted, if one sensor measuring the pitch of the plane's nose malfunctions, the automatic system can send the plane into a dive. One wonders, as one commentator pointed out, who designed a critical system where just one of two sensors malfunctioning could doom a plane?

But back to snow — it can snow when it is climatologically unlikely as in the super snowstorm of December 13, 2013. But, the relatively strong spring sun now means that we would need a very dark and persistent cloud cover, or a nighttime storm, to bring about any accumulation.

It all seems so unlikely, so why mention it? Because it is in the monthly forecast — and ignoring the possible can have very dangerous consequences.

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. Click here to read more of this writer’s work in The Jerusalem Herald.


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

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(Isaiah 40:9)

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