Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 5:31 PM GMT on January 16, 2014
Record warmth and dryness have hit California this month, as one of the worst drought in state history continues to intensify. San Francisco Airport observed its warmest January day on record on Wednesday: 73°. This beat the previous all-time January record of 72° set twice before (on January 13, 2009 and January 24, 1948). Oakland hit 77° on Wednesday, and Monterey topped out at a remarkable 83°--which would be a daily record on many summer days. The record January heat has been accompanied by record dryness. California recorded its driest year in its history during 2013. The most widely used measure of drought in the U.S., the Palmer Drought Severity Index (PDSI), shows that December 2013 drought conditions in California were the 2nd most intense for any December going back to 1895, with only December 1898 being worse. If we look at 3-month PDSI for the first three months of the water year, October - December, 2013 ranks as the third worst such drought, behind 1898 and 2008.
Figure 1. Palmer Drought Severity Index (PDSI), shows that December 2013 drought conditions in California were the 2nd most intense for any December going back to 1895. Only December 1899 was worse. Image credit: NOAA/NCDC.
The forecast: no relief in sight
Less than an inch of precipitation has fallen over more than 95% of the state so far in January 2014, and the prospects for significant rain for the next ten days look bleak. A large and persistent ridge of high pressure has set up over the West Coast and shows no signs of budging. Since rain-bearing low pressure system tend to travel along the axis of the jet stream, these storms are being carried well to the north of California into Southeast Alaska, leaving California exceptionally dry. Today's U.S. Drought Monitor showed that the area of California experiencing extreme drought expanded from 28% to 63% over the past week, and I expect January 2014 drought conditions will challenge 1899 for the dubious honor of worst January drought in state history.
Figure 2. Color-coded wind speeds at a pressure of 300 mb (roughly 9,000 meters or 30,000 feet) from 00 UTC January 16, 2014, show the axis of the jet stream over North America, with a large upside-down "U"-shaped ridge of high pressure over the West Coast. California is outlined in orange. The strongest winds of the jet stream (orange colors, 160 mph) were observed over the Northeast United States. Image generated from the 00 UTC January 16, 2014 run of the GFS model, and plotted using our wundermap.
Top ten most severe winter drought months in California history, 1895 - 2013, along with the Palmer Drought Severity Index (PDSI) for the month:
1) Feb 1899, -6.28
2) Feb 1991, -6.21
3) Jan 1991, -5.74
4) Jan 1899, -5.67
5) Feb 1977, -5.62
6) Dec 1898, -6.28
7) Jan 2009, -5.26
8) Jan 1977, -4.82
9) Dec 2013, -4.67
10) Feb 2009, -4.49
Our weather historian, Christopher C. Burt, has much more detail on this historic drought in his latest post, Central California Enters a Drought Period Unprecedented in its Weather History.
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