Rain record reached in north state

This graph displays the cumulative amount of precipitation for the northern Sierras and Cascades so far this water year, 2016-2017 (darker line). This water year surpassed the previous record holder, 1982-1983 (lighter line), on April 11. The box at bottom right lists the previous record holders. Image from the National Weather Service, Sacramento

“We did it.” Craig Shoemaker, meteorologist with the National Weather Service in Sacramento, told the Mercury News, “We didn’t just beat the record, we shattered it.”

As of 4 a.m., on April 13, northeastern California broke its historic record for how much precipitation is received in a water year.

If we have to put up with the rain anyway, it’s nice to have a silver lining. Like going to football game where you have to sit through the cold and rain, but are rewarded when the game turns out to be a notable one.

Precipitation during this water year so far is equivalent to 90 inches of rain, which is more than twice the historic average.

El Nino or no El Nino

This new record was set just five days after Governor Jerry Brown, Jr. issued an order on April 7 officially ending his five-year drought emergency order.

Also, the water year 2016-2017 is not an El Nino year. El Nino years tend to have increased precipitation along the West Coast as compared with normal years.

Yet, water year 2016-2017 has overwhelmed the previous record holder, 1982-1983, which occurred during one of the strongest El Nino events on record

A water year starts on Oct. 1 and end on Sept. 30, so the state  still has time left to run up the score.

Snow pack

Due to relatively warm temperatures, much of the snow received this winter was washed off the mountains during rain-on-snow events.

Therefore, though the current snow pack is relatively good, its total water content does not match that of the previous precipitation contender, water year 1982-1983.

This graph displays the water content of snow packs in northern California for various years. Overall precipitation, rain and snow, in water year 2016-2017 has already exceeded precipitation in water year 1982-1983, the previous record holder. However, the water content of our current snow pack does not match that of the snow pack that existed in 1982-1983. Image from the National Weather Service, Sacramento

What’s going on?

Strong storms, traveling from west to east across the Pacific Ocean, usually peter off in this area by April, as storm tracks have normally moved further north by then.

However, this year the storms just keep on coming and the region can expect more rain and snow, at least for a while.

One reason for this may be that there has been a very strong high pressure zone located north of the Pacific Ocean this winter.

  This high pressure zone has kept low pressure cells containing storms from moving north as they are also migrating from west to east across the Pacific.

This time of year, high pressure represents colder, denser air.

Low pressure cells and storms, represent warm, less dense air. These low pressure cells generally move north from the hot, moist tropics, carrying warm, moist air with them.

Like a quarterback trying to move through a hefty defensive line, the low pressure cells can’t move north through the high pressure zone. So, the storms have to make an end run around the high pressure before they can move north.

The greater the temperature difference from the equator to the North Pole, the greater the differences in air pressure between stationary high pressure zones and migrating low pressure cells.

Higher temperatures during the winter months can change the relative blocking strength of high pressure zones and thus change where storms travel and where moisture is released.

Varying temperatures thus cause changes in where storms travel and where precipitation is released.

Air pressure from Eastern Asia eastward across the Pacific Ocean and North America to Greenland. Darker Hs represent high pressure zones. Lighter Ds represent low pressure cells (storms). Large stationary high pressure zones to the north are keeping migrating storms from migrating north as they move from west to east across the Pacific Ocean. This has concentrated storms along the west coast of North America this winter. National Weather Service Ocean Prediction Center