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Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.Crunch Time for California Drought
Crunch Time for California Drought
The most dangerous month of the year for wild fires is underway in California and starting off with a significant heat wave. Last week’s rainfall had little impact on the overall drought conditions but was a welcome respite nevertheless and hopefully a harbinger of some drought relief as the rainy season approaches.
Welcome rainfall of 0.30” to over 3” brought relief to the northern half of California on September 24-26 and helped squelch the massive King Wild Fire but, unfortunately, they hardly made a dent to the state’s overall drought situation and ground moisture conditions, let alone reservoir levels.
A comparison of the Drought Monitor maps at the beginning of the dry season in May and the latest map issued. The latest drought map (top) released on October 2nd shows only an imperceptible improvement in conditions (in the far northwestern county of Del Norte) following the rainfall during the last week of September. Map from NOAA/NCDC et al.
As the U.S. Drought Monitor reported in their Western Regional text summary, ”The rains had little impact on the ongoing drought, especially in California, where deficits are huge and the normal annual precipitation in parts of the northern coastal areas can reach 75-100 inches. Topsoil in a few areas benefited, wildfires were hindered, and stream flow increased, but the stream flow recovery was short-lived as streams rapidly returned to the low flows they had prior to the rain event, and reservoir levels did not improve. Statewide, California soil moisture conditions were the same as last week, with 80% of topsoil and 85% of subsoil rated short or very short of moisture by the USDA.”
To make matters worse, a significant heat wave has now engulfed the state and raised the specter of more wild fires to come. Temperatures on Thursday, October 2nd, broke records in southwestern California where Santee, Ventura, and Fullerton all hit 102°F (38.9°C), the warmest places in the nation. Santa Maria, on the normally cool coastline hit 100°F (37.8°C) breaking its previous daily record of 96°F (35.6°C) set in 1945. Long Beach (in the Los Angeles area) had a record 98°F (36.7°C) beating out the former record for the date of 96°F (35.6°C) also set in 1945. The San Francisco Bay Area was also hot, but not in record territory. Salinas was the warm spot reaching 97°F (36.1°C) and San Francisco (airport location) reached 91°F (32.8°C), its 2nd hottest day of the year so far (following a 92°F/33.3°C reading on May 13th). Although impressive, October often registers the hottest temperatures of the year for coastal locations in the state. Monterey’s hottest temperature on record occurred on October 5, 1987 when a scorching 104°F (40°C) was observed and it was 102°F (38.9°C) in Downtown San Francisco, its October monthly heat rtecord. Eureka’s all-time heat record happened even later in the month, on October 26, 1993 with an 87°F (30.6°C) reading. San Francisco has seen several occasions of 100°F+ temperatures during October. SATURDAY UPDATE: On Friday, October 3rd, record temperatures continued. San Francisco Airport reached 95°F and San Francisco Downtown 92°F, both figures represent the warmest temperatures observed so far this year. Pacifica, right on the coast, reached 96°F. A little further south, Gilroy peaked at 105°F, the hottest place in the nation on Friday. Monterey measured a daily record high of 96°F. Santa Cruz was 99°F. SUNDAY UPDATE: San Francisco Airport reached 91°F on Saturday, October 4th. This was the 3rd consecutive day with temperatures above 90°F. The last time this occurred was over six years ago on June 19-21, 2008. If the temperature hits 90°F on Sunday it would be the first time with four consecutive 90°+ days in 10 years, the last time being September 4-7, 2004. Oakland registered a new daily record high of 92°F.
Here are the monthly maximum temperatures observed so far this year at Downtown San Francisco:
JAN: 72° on Jan. 15
FEB: 69° on Feb. 21
MAR: 76° on Mar. 15
APR: 90° on Apr. 30
MAY: 90° on May 13
JUN: 78° on 2 occasions
JUL: 85° on Jul. 25
AUG: 71° on 3 occasions
SEP: 80° on Sep. 10
OCT: 92° on Oct. 3 (so far)
Notice how it actually got warmer in January than it ever did in August!
The cause for the October warmth is when the first outbreaks of cold air from Canada invade the Rocky Mountain states which causes a high pressure ridge to build over California and strong offshore flow winds to form at the surface. These are the same winds (known as the Santa Ana and Diablo winds) that have caused some of California’s worst wild fires on record. Fortunately, during the current heat wave, very strong offshore winds are not forecast to develop. In any case, the heat wave is expected to last through the weekend with even hotter temperatures expected at most locations on Friday and Saturday (I will update the numbers and new records this weekend).
Needless to say, the hot dry conditions have completely eliminated the beneficial effects of the September rainfall, and conditions have set the stage for a critical month, both in terms of the drought and potential wild fires. Reservoir capacities continue to shrink: Lake Oroville, one of the state’s most important water storage facilities, is now down to 30% capacity, approaching its all-time record low of 26% set in 1977 during the state’s worst drought on record.
Lake Oroville when at full capacity in 2011 (top) and in August, 2014 (bottom) when it had shrunk to 32% capacity. Since August it has declined to 30% capacity. Photos by Paul Hames, California Department of Water Resources and Justin Sullican, Getty Images.
Statewide reservoirs are at 36% capacity, which is 57% of normal for this time of the year.
State-wide reservoir levels as of October 2nd. Map from the California Department of Water Resources.
Meanwhile, the crisis is worsening for the state’s farmers and residents, especially in the Central Valley as this report from the New York Times dramatically relates.
In a normal year, the winter rainy season should begin around the third week of October for the northern third of California and gradually work its way south with each succeeding week until mid-November when regular rainfalls should become statewide. Everyone is keeping his or her fingers crossed!
Christopher C. Burt
Weather Historian
The most dangerous month of the year for wild fires is underway in California and starting off with a significant heat wave. Last week’s rainfall had little impact on the overall drought conditions but was a welcome respite nevertheless and hopefully a harbinger of some drought relief as the rainy season approaches.
Welcome rainfall of 0.30” to over 3” brought relief to the northern half of California on September 24-26 and helped squelch the massive King Wild Fire but, unfortunately, they hardly made a dent to the state’s overall drought situation and ground moisture conditions, let alone reservoir levels.
A comparison of the Drought Monitor maps at the beginning of the dry season in May and the latest map issued. The latest drought map (top) released on October 2nd shows only an imperceptible improvement in conditions (in the far northwestern county of Del Norte) following the rainfall during the last week of September. Map from NOAA/NCDC et al.
As the U.S. Drought Monitor reported in their Western Regional text summary, ”The rains had little impact on the ongoing drought, especially in California, where deficits are huge and the normal annual precipitation in parts of the northern coastal areas can reach 75-100 inches. Topsoil in a few areas benefited, wildfires were hindered, and stream flow increased, but the stream flow recovery was short-lived as streams rapidly returned to the low flows they had prior to the rain event, and reservoir levels did not improve. Statewide, California soil moisture conditions were the same as last week, with 80% of topsoil and 85% of subsoil rated short or very short of moisture by the USDA.”
To make matters worse, a significant heat wave has now engulfed the state and raised the specter of more wild fires to come. Temperatures on Thursday, October 2nd, broke records in southwestern California where Santee, Ventura, and Fullerton all hit 102°F (38.9°C), the warmest places in the nation. Santa Maria, on the normally cool coastline hit 100°F (37.8°C) breaking its previous daily record of 96°F (35.6°C) set in 1945. Long Beach (in the Los Angeles area) had a record 98°F (36.7°C) beating out the former record for the date of 96°F (35.6°C) also set in 1945. The San Francisco Bay Area was also hot, but not in record territory. Salinas was the warm spot reaching 97°F (36.1°C) and San Francisco (airport location) reached 91°F (32.8°C), its 2nd hottest day of the year so far (following a 92°F/33.3°C reading on May 13th). Although impressive, October often registers the hottest temperatures of the year for coastal locations in the state. Monterey’s hottest temperature on record occurred on October 5, 1987 when a scorching 104°F (40°C) was observed and it was 102°F (38.9°C) in Downtown San Francisco, its October monthly heat rtecord. Eureka’s all-time heat record happened even later in the month, on October 26, 1993 with an 87°F (30.6°C) reading. San Francisco has seen several occasions of 100°F+ temperatures during October. SATURDAY UPDATE: On Friday, October 3rd, record temperatures continued. San Francisco Airport reached 95°F and San Francisco Downtown 92°F, both figures represent the warmest temperatures observed so far this year. Pacifica, right on the coast, reached 96°F. A little further south, Gilroy peaked at 105°F, the hottest place in the nation on Friday. Monterey measured a daily record high of 96°F. Santa Cruz was 99°F. SUNDAY UPDATE: San Francisco Airport reached 91°F on Saturday, October 4th. This was the 3rd consecutive day with temperatures above 90°F. The last time this occurred was over six years ago on June 19-21, 2008. If the temperature hits 90°F on Sunday it would be the first time with four consecutive 90°+ days in 10 years, the last time being September 4-7, 2004. Oakland registered a new daily record high of 92°F.
Here are the monthly maximum temperatures observed so far this year at Downtown San Francisco:
JAN: 72° on Jan. 15
FEB: 69° on Feb. 21
MAR: 76° on Mar. 15
APR: 90° on Apr. 30
MAY: 90° on May 13
JUN: 78° on 2 occasions
JUL: 85° on Jul. 25
AUG: 71° on 3 occasions
SEP: 80° on Sep. 10
OCT: 92° on Oct. 3 (so far)
Notice how it actually got warmer in January than it ever did in August!
The cause for the October warmth is when the first outbreaks of cold air from Canada invade the Rocky Mountain states which causes a high pressure ridge to build over California and strong offshore flow winds to form at the surface. These are the same winds (known as the Santa Ana and Diablo winds) that have caused some of California’s worst wild fires on record. Fortunately, during the current heat wave, very strong offshore winds are not forecast to develop. In any case, the heat wave is expected to last through the weekend with even hotter temperatures expected at most locations on Friday and Saturday (I will update the numbers and new records this weekend).
Needless to say, the hot dry conditions have completely eliminated the beneficial effects of the September rainfall, and conditions have set the stage for a critical month, both in terms of the drought and potential wild fires. Reservoir capacities continue to shrink: Lake Oroville, one of the state’s most important water storage facilities, is now down to 30% capacity, approaching its all-time record low of 26% set in 1977 during the state’s worst drought on record.
Lake Oroville when at full capacity in 2011 (top) and in August, 2014 (bottom) when it had shrunk to 32% capacity. Since August it has declined to 30% capacity. Photos by Paul Hames, California Department of Water Resources and Justin Sullican, Getty Images.
Statewide reservoirs are at 36% capacity, which is 57% of normal for this time of the year.
State-wide reservoir levels as of October 2nd. Map from the California Department of Water Resources.
Meanwhile, the crisis is worsening for the state’s farmers and residents, especially in the Central Valley as this report from the New York Times dramatically relates.
In a normal year, the winter rainy season should begin around the third week of October for the northern third of California and gradually work its way south with each succeeding week until mid-November when regular rainfalls should become statewide. Everyone is keeping his or her fingers crossed!
Christopher C. Burt
Weather Historian
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.