NOTE: Thanks to the proofreaders who caught my dyslexia ;-). Also added some information from another diary on the importance of heat stress on vegetation (i.e. crops!) and added a few clarifying words in other spots.
Here, have some corn ... :-(
MAY-JULY and JULY CLIMATE
Precipitation over the breadbasket of the US has been deficient for months, ever since we experienced the warmest March in the continental US (CONUS) on record. The precipitation percentage departure from normal over the Great Plains Region for the last 90 days is below. Anything red or darker is less than 50% of normal. Those brick red colors you see in a few places are anywhere from 5-25% of normal. Keep in mind that this is the wettest time of year for many of these places.
- Hot weather increases evaporation, and this year in particular, started the growing season (and the demand of vegetation for soil moisture) about three weeks early. So that was three extra weeks of demand on soil water stores.
- Vegetation cannot take extreme heat, and will shut down at very high temperatures.. See 8ackgr0und N015e's diaryon that topic from late last month during one of the spikes in this summer's heat waves.
IMPACTS on SOIL MOISTURE
The percent of each state with short or very short soil moisture in the top 6" of soil is shown below. Some states are almost completely deficient, including IL at 100%. IA, NE, KS, MO, IN, and OK are all at greater than 90% short or very short. With precipitation, this soil will have to be saturated for any water to effectively move further down into the vegetation root zone and to the ground water below.
IMPACTS ON AGRICULTURE
The following two graphics show the percentrage by state of corn and soybeans in poor and very poor condition as of 29 July 2012. In the case of corn, it's the largest area with such conditions since 1988, the last major drought, with 48% of the crop poor or very poor. For soybeans, it's the largest area in the record at 37% poor or very poor. For both crops, the area with these conditions increased from the previous week.
This graphic shows the percentage of the US corn, soybean, and pasture and range (for cattle feeding) conditions for all categories on 29 July 2012. Very little of the crop is in good or very good condition. Pasture and range conditions pretty much mirror those for corn and soybeans. Some farmers are prematurely slaughtering their cows and pigs because they cannot afford to feed them, and/or the heat is increasing the risk that they will die before they can be brought to market.
The Climate Prediction Center at the National Centers for Environmental Prediction have posted their usual week-2, monthly, and three-month outlooks. The graphics below show the probabilities of precipitation being above or below normal (green and brown shades, respectively) for those three periods. No shading means equal chances of above or below normal precipitation. Note the brown in the middle of the CONUS.
If El Niño occurs this winter, which now looks more likely than not, analogs to other El Niños tell us that it is more likely to be dry in the drought areas than wet, and more likely warm than dry. The 2009-10 El Niño was an exception, with wet, cold weather over much of the country. La Niñas are typically opposite in character from El Niños, and 2010-11 and 2011-12 were both La Niña seasons. 2010-11 mostly conformed to this rule though it was colder than normal, rather than warmer than normal, in the southern tier of the CONUS. 2011-12 was warm and dry almost everywhere.
Whether climate change makes the usual equatorial Pacific/El Niño/La Niña relationships not work as well, or the last few years have been a random fluke of nature, we can't yet say with certainty. That being said, the following is a November through January precipitation composites for previous El Niño events from the US National Centers for Environmental Prediction's Climate Prediction Center.