Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 5:01 PM GMT on December 28, 2012
Rain and snow from the massive winter storm that swept across the nation over the past week put only a slight dent in the Great Drought of 2012, according to the latest U.S. Drought Monitor report. The area of Iowa in extreme or exceptional drought fell 9 percentage points to 32 percent, thanks to widespread precipitation amounts of 0.5" - 1.5". However, the area of the contiguous U.S. covered by moderate or greater drought remained virtually unchanged from the previous week, at 61.8%. According to NOAA's monthly State of the Drought report, the 61.8% of the U.S. covered by drought this week was also what we had during July, making the 2012 drought the greatest U.S. drought since the Dust Bowl year of 1939. (During December of 1939, 62.1% of the U.S. was in drought; the only year with more of the U.S. in drought was 1934.) The Great Drought of 2012 is about to become the Great Drought of 2012 - 2013, judging by the latest 15-day precipitation forecast from the GFS model. There is a much below-average chance of precipitation across the large majority of the drought region through the second week of January, and these dry conditions will potentially cause serious trouble for barge traffic on the Mississippi River by the second week of January. The river level at St. Louis is currently -3.6', which is the 9th lowest level of the past 100 years. The latest NOAA river level forecast calls for the river to fall below -5' by January 4. This would be one of the five lowest water levels on record for St. Louis. At this water level, the river's depth will fall to 9' at Thebes, Illinois, which is the threshold for closing the river to barge traffic. The Army Corps of Engineers is working to dredge the river to allow barge traffic to continue if the river falls below this level, but it is uncertain if this will be enough to make a difference, unless we get some significant January precipitation in the Upper Mississippi watershed. The river is predicted to set a new all-time low by January 13 (Figure 4.)
Figure 1. The December 25, 2012 U.S. Drought Monitor showed that approximately 62% of the contiguous U.S. was in moderate or greater drought.
Figure 2. Predicted 7-day precipitation for the period ending on Friday, January 4. Very few regions of the main U.S. drought area are predicted to receive as much as 0.5" of precipitation (dark green color.) Image credit: NOAA.
Long-term drought outlook
NOAA's December 20 Seasonal Drought Outlook called for drought to persist over at least 80% of the U.S. drought area through the end of March. I don't see any signs of a shift in the fundamental large-scale atmospheric flow patterns during the past few weeks, or in the model forecasts for the coming weeks, and it is good bet that drought will be a huge concern as we enter spring. NOAA's Climate Prediction Center predicts an increased chance of drier than average conditions over southwestern portions of the drought region during the coming three months. In general, droughts are more likely in the Central U.S. when warmer than average ocean temperatures prevail in the tropical Atlantic, with cooler than average ocean temperatures in the tropical Eastern Pacific (La Niña-like conditions.) This is the current situation, though the equatorial tropical Pacific is only slightly cooler than average (0.2°C below average as of December 24). Most of the Midwest needs 3 - 9" of precipitation to pull out of drought.
Figure 3. Amount of precipitation needed to bust drought conditions over the U.S., according to NOAA's Climate Prediction Center. Eastern Oklahoma and Western Arkansas need the most rain, 9 - 15".
Figure 4. The latest NOAA river level forecast calls for the Mississippi River to fall below -5' at St. Louis by January 4. At this level, the river may close to barge traffic due to low water. By January 13, the river is expected to fall to its lowest level on record, -6.2'. The record was set in January 1940, after the great Dust Bowl droughts of the 1930s.
Figure 5. This Nov. 28, 2012 photo provided by The United States Coast Guard shows a WWII minesweeper on the Mississippi River near St. Louis, Missouri. The minesweeper, once moored along the Mississippi River as a museum at St. Louis before it was torn away by floodwaters in 1993, is normally completely under water. However, it has become visible--rusted but intact--due to near-record low river levels on the Mississippi. (AP Photo/United States Coast Guard, Colby Buchanan)
My post on Lessons from 2012: Droughts, not Hurricanes, are the Greater Danger discussed how drought is our greatest threat from climate change.
Ricky Rood blogs about the Dust Bowl
Have a great weekend, everyone!
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