A look at winter forecasts for 2014

Outlook_map_Precip_203F

NOAA’s winter forecast predicts ongoing drought conditions for the southwest, and ‘equal chances’ for California

Will the winter be wet or dry? On the heels of two dry years and in light of the recent announcement of the low 5% initial allocation for state water as well as rumors of some federal contractors receiving an allocation of 0%, it’s the question on every water manager’s mind.

According to the Farmer’s Almanac, a decline in solar activity combined with ocean-atmosphere patterns in the Pacific will bring us below-normal temperatures and lots of precipitation.  And if you take your signs from acorns, the hair on a bear’s back, or hungry critters seemingly stocking up for a rough winter ahead, the signs are good.

However, if you prefer to consider things such as sea surface temperatures and the like, the news is not quite so positive.  The NOAA’s long-term winter forecast is predicting little relief for the drought-stricken southwest and equal chances for above, near, or below-normal precipitation for California.  With conditions considered ENSO-neutral, meaning neither an El Niño or a La Niña event is in play to influence weather patterns, there isn’t much to go on.

“It’s a challenge to produce a long-term winter forecast without the climate pattern of an El Niño or a La Niña in place out in the Pacific because those climate patterns often strongly influence winter temperature and precipitation here in the United States,” said Mike Halpert, acting director of NOAA’s Climate Prediction Center. “Without this strong seasonal influence, winter weather is often affected by short-term climate patterns, such as the Arctic Oscillation, that are not predictable beyond a week or two.”

The Department of Water Resources has been working with researchers to develop an experimental winter outlook forecast, hoping to able to develop and improve forecasting skills up to a year in advance.  With the ENSO-neutral conditions not providing a signal, the experimental forecasts consider other influences, such as the status of the Pacific Decadal Oscillation (PDO), the Atlantic Multidecadal Oscillation,  the Madden-Julian Oscillation, and recent Alaskan temperatures.

This year’s forecast, prepared by Dr. Klaus Wolter of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado, predicts mostly dry conditions for California and near-normal to dry conditions for the Colorado Basin.

However, since California’s annual water supply is determined by a relatively small number of storms,  things could change rapidly.  “Atmospheric river (AR) storms are a wildcard in this forecast,” said Wolter.

Michael Anderson explained the phenomena of atmospheric rivers at a recent NWRI drought workshop“This is concentrated moisture happening in the first 5000 feet of the atmosphere that goes right across the ocean and runs into California, and what do you suppose it runs into,” he said. “We have some hills that get in the way, and they’re actually very effective in making that water fall out of the sky, but again it depends on the dynamics of that winter storm system that are driving it.  If it’s a warm system, there’s a lot of rain that can happen, and if it happens for a long enough duration, there is flooding.  If it’s a colder storm, these can be absolutely fantastic for water supply.”

HMT

The Hydrometeorology Test Bed (HMT)
California’s cutting edge technology for monitoring atmospheric river (AR) storms

Researchers have set up a cutting-edge monitoring system in California to track these storms and conditions.  “It’s great we found out about them, but now we need to start documenting that so we can start following along and looking at how a warmer atmosphere that might hold more water, how that might relate in terms of its sudden delivery to California,” Anderson said.

“New work is showing possible relationships between precipitation and phase of the Madden-Julian Oscillation (MJO), and between phase of the MJO and conditions favoring AR storms”, said Jeanine Jones of DWR. “DWR plans to collaborate with the research community to see how this information could continue to be developed to improve forecasting at timescales useful for water management”.

So how much precipitation Mother Nature decides to deliver to us remains to be seen, and even if precipitation is average, it won’t translate into average runoff, warned Jones.  “As we go into this year, we have generally dry antecedent conditions, so even if we get average runoff, a lot of that will be lost to replenishing soil moisture and those kinds of things,” she said.  “We know that storage in groundwater basins has been depleted, especially in some of the fractured rock basins that are critical for small water systems, and we know that in areas where there have been wildfires, there is a high potential for mud and debris flows and after effects of that.”

If 2014 is dry, wildfire will be the biggest risk in terms of its economic, public health and safety impacts, and small water systems, those with less than 500 connections, are especially at risk.   “Many of those systems struggle to maintain water supplies even in wet years, let alone average or dry years,” said Jones.  “They tend to be located in areas outside of a large municipal provider and they often have fractured rock groundwater sources which tend to be quite unreliable.”

So in light of low reservoir levels and continuing dry conditions, the Department of Water Resources issued an initial allocation of only 5%.  However, officials reminded the public that the initial estimates are dictated primarily by water storage levels and are typically low because they are made before the wettest period of the year, and commonly are increased as winter storms accumulate precipitation in the Sierras.

The lowest previous initial allocation for state water, also 5%, was in 2010; it was eventually increased to 50% as conditions improved.  In 2011, an initial allocation of 25% was improved to 80% as the season progressed.  And miracles have occurred – in 1993, an initial allocation of 10% was increased to 100% as a series of winter storms battered the state.

The final State Water Project allocation for 2013 was 35%; in 2012, the final allocation was 65%.

“We hope things improve with this winter’s storms,” said DWR Director Mark Cowin, “but there is no guarantee that 2014 won’t be our third consecutive dry year.  Today’s allocation is a stark reminder that California’s fickle weather demands that we make year-round conservation a way of life.”

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Written by Chris “Maven” Austin