Rain sweeps nation for fifth day

In the year 2000, 219 mm. were measured in the month of October at the Mikve Yisrael station - making the current amounts "very close," he said.

By SHARON UDASIN
Updated: OCTOBER 30, 2015 04:20
Stormy weather in Israel
Heavy rain continued on Thursday, drenching Israelis and flooding traffic arteries for a fifth day in a row.
Beginning in the late morning, Thursday’s precipitation began in the Coastal Plain, then moved inland and eventually to the Jordan Valley, greatly diminishing in quantity by the late afternoon, Dr.
Amos Porat, head of the Climate Department at the Israel Meteorological Service, said.
There was flooding on both city streets and intercity highways, with the worst disruption on Route 90 in the Arava Desert, north of Eilat.
In the early afternoon, the flooding on Route 90 swept away a couple trapped in their car, necessitating a helicopter rescue, the police’s Arava search and rescue unit said.
Two youths also required rescue, after they were stranded near the Tzin Bridge west of Nahal Tzin, which had become a gushing river, the unit added.
Rain has been bountiful over the past month, exceeding October averages fivefold in some areas. At the IMS monitoring station in Shefayim, north of Herzliya, the rainfall matched all-time records for the month, reaching 219 mm.
Nonetheless, Porat explained, national records were not broken as the heaviest rain fell in limited areas.
Nir Stav, deputy director of the IMS, told The Jerusalem Post on Thursday evening, “October is a crazy month in Israel, not only on the ground but also in the atmosphere. You sometimes have a very dry October and sometimes you have floods. It’s really fluctuating.
“What we have here are bursts of rain, you have showers,” he said. “Those events are intense but of very short duration.
One event can change the month. When you talk about the rain of October, sometimes when you look at the historical record, you have only one day or a few hours of rain in October, and sometimes you have several days and sometimes a week. It’s very different year to year.
“I think it’s maybe the month with the greatest variability in the calendar in terms of rain,” Stav added. “So it’s not very practical to talk about the average in October.”
On Thursday, the most rain – 27 mm. – accumulated at the IMS’s Beit Dagan station, located near Rishon Lezion, according to data provided by Porat.
Since the storm began on Sunday, 40-80 mm. fell in most areas of the Coastal Plain and the Shfela region, with much more accumulated in isolated spots: more than 100 mm. in portions of the Sharon region (124 mm.
in Ra’anana, 148 mm. in Shefayim) and in the Gaza perimeter (112 mm. at Kibbutz Erez). Relatively large quantities were also measured in typically dry areas, such as 42 mm. at Kibbutz Gilgal in the Jordan Valley, 37 mm.
in Sodom, 35 mm. in Mitzpe Ramon and 31 mm. in Yotvata.
Over the course of the storm, the Judean Hills received only about 20-25 mm. and the northern mountains just about 10-25 mm.
Mass power outages, mostly in the Sharon region and the surrounding cities from Sunday through Wednesday, had been repaired by Wednesday evening, but many cities continued to experience flooding on Thursday.
Although acknowledging that he is not an authority on drainage, Stav said he assumed that much of the urban flooding was caused by trees, branches and leaves that were “scattered all over because of the gusty winds” on Sunday.
“They could devastate the drainage system,” he said.
“Therefore, when the rain arrived, the system was not able to do its job. But this is just speculation.”
The five-day storm was the result of an upper air trough accompanied by a Red Sea trough in its lower levels, Porat explained on Sunday.
A meteorological trough is an elongated region that features low atmospheric pressure, as opposed to a ridge, which features high atmospheric pressure.
“Those clouds that arrived on Sunday were not typical Israeli clouds,” Stav said on Thursday. “They were more like the clouds you encounter in the Southwest [United] States, those tornado-producing and big hail-producing thunderstorms.”
Such “super thunderstorms” require tropical or subtropical conditions, with high humidity and a thick atmosphere to sustain the clouds, he explained.
“We get severe thunderstorms only in either autumn or in spring,” Stav said. “We never get them in the middle of the winter.”
This time, an influx of high humidity arrived to the region from the South Atlantic, entering the Mediterranean on October 19 and gradually making its way to Israel, he continued. Just days before the system hit Israel, Greece experienced floods, following similar events in Italy, Stav explained.
Both the sea and atmosphere stayed warmed enough, with just the right conditions for the storm to develop.
“This entire mixture created something very unique,” Stav said.
For Friday, the IMS forecasts partly cloudy skies with isolated showers in the northern and central regions, accompanied by a light risk of flash floods in the eastern wadis and a slight rise in temperatures.
Partly cloudy to fair conditions are expected on both Saturday and Sunday, with a rise in temperatures both days.
Although partly cloudy conditions will likely persist on Monday, with no significant change in temperatures, the IMS warned of possible showers and flash flood risks in the eastern regions, with strong winds blowing over the northern and mountain regions.