By Darren Peck

SAN FRANCISCO (CBS SF) — As extreme drought conditions continue to expand across the San Francisco Bay Area, a leading climate researcher issued a new warning Thursday of another sign that a water supply crisis is developing across the region.

Dan McEvoy, a researcher with the Western Region Climate Center, told KPIX 5 he was startled to discover that several locations in Sierra had seen the biggest decline in snowpack’s water content on record for the time span covering the first three weeks of April.

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At several key reporting locations across the Sierra range, the water content being stored within the snowpack has lost almost half of what was there at the start of the month.

That comes in the wake of a California’s Department of Water Resources survey on April 1 which found the snowpack in the central Sierra was 63% of the average or 16.5 inches.

Typically the snowpack is at its highest on April 1. However, since that date, the snowpack in the central Sierra has declined significantly to just 37% of average.

McEvoy said while many factors were at play in such an alarming rate of loss, the primary culprit is the intense warmth California experienced over the past month. Much of Northern California experienced temperatures 4-degrees above average for the period.

“It may not sound like a lot, but averaged out over an entire month, 4 degrees is quite a lot,” said KPIX 5 meteorologist Darren Peck.

On Thursday, federal water officials release their latest U.S. Drought Monitoring statistics. Extreme drought conditions continued to expand with Solano County and parts of Contra Costa and Alameda counties now added to a growing federal list of California regions facing water supply challenges.

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For weeks, Lake, Napa, Mendocino counties and a wide swath of Sonoma County have fallen in the extreme drought category with the remaining Bay Area regions experiencing conditions that fall under a severe drought designation.

ALSO READ: KPIX 5 California Drought 2021 Special Section

Now, the daunting red area of extreme drought on the map has expanded south and eastward.

Click To View Updated U.S. Drought Monitor Map

Federal drought officials said a year ago less than 5 percent of California was experiencing extreme drought conditions. This week that had grown to nearly 50 percent of the state.

According to the National Weather Service, downtown San Francisco is currently experiencing its 4th driest rainy season with just 8.72 of precipitation.

Gov. Gavin Newsom was in Mendocino County declaring a drought emergency on Wednesday, and while it specifically applies to Mendocino and Sonoma counties, the entire North Bay is already struggling with drought conditions.

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“Oftentimes we overstate the word historic, but this is indeed an historic moment, certainly historic for this particular lake, Mendocino,” Newsom said, standing where 40 feet of lake water was supposed to be. The lake is at about 40% of normal capacity.

Darren Peck