Soybean Soil Moisture Running Down, Rainfall Needed

August 19, 2011

The USDA issued a low soybean yield in the first official estimate of the new season.   The August report last week, reflecting August 1 conditions, indicated  a national yield of  41.4 bushel per acre and 5% below trend. 

 

Since the beginning of the month,  drought conditions have worsened in soybeans.   Month-to-date rainfall has accumulated to only 1.68 inches,  as a weighted soy average,  and 70%  of normal.    That compares to  2.9 inches last year,  and 20% above-normal .      The US soybean yield in 2010 was  slightly above trend with 43.5 bushels per acre. 

 

 

August Rainfall Key To Soybean Yield

 

August is the month when rainfall matters the most for soybean in the key pod-filling stage.   When August rainfall is very heavy, soybeans in the pod are much larger.   Under ideal wet conditions,  4 beans may even develop instead of the 3 beans normally.     There is ample evidence in history showing the best yields occur in wet Augusts.    

 

 

Forecast More Hopeful For Rain

 

The new forecast is hopeful for generous rainfall in many key growing areas.   Heaviest rainfall would occur in the southern Midwest,  Delta and Mid South.       The  northern Midwest  would be slighted,  receiving around .50 - .60  inch  in South Dakota, Minnesota, Wisconsin and the Great Lakes area farms.   Normal weekly rainfall is .90 inch in late August.

 

Strong thunderstroms erupted early this morning in Missouri and Illinois.   Some 2-inch rains occured in central  Missouri but Illinois rainfall was more scattered and mostly under 1 inch. Southeast  Missouri got heavy rain  1.5-inches in scattered thunderstorms.     

 

Unstable weather is expected to continue with a high risk of thunderstorms in the next few days.   More details are coming in the Friday weather forecast summary.   See where soybeans are grown.    

Monsoon Wind Circulation Pronounced

 

The Southwest monsoon is the driver for strong thunderstorms  delivering  humid, unstable air to the US heartland .  The pronounced wind circulation would continue from the Mexico tropics north and east into to the US heartland.       Showers are  “ridge-rider”  thunderstorms tracking along the northern rim of large heat dome in the southern United States.

 

 

 

Is this La Nina?

 

The rainfall pattern just described is very similar to the “weak” La Nina case in the July-September period.     The La Nina effect has been strengthening,  evidenced by steady cooling the past month in the equatorial Pacific Ocean. 

 

 

See the La Nina rainfall  July-September, and based on 7 previous episodes.   This analysis comes from the Climate Prediction Center.   It indicates a propensity toward drought in the  Midwest northern areas which, this year is beginning to manifest:

 

 

Not matching the La Nina pattern is the ongoing severe drought in Texas and Oklahoma.  Normally this area would be rather  wet.   The Southeast United States is dry also, when heavy rain ought to be occurring.  Perhaps a tropical storm will track up the Southeast US coast in September, changing the dry pattern.  

 

The cooler forecast for the Northern Midwest is reflected in the  La Nina tempertures,  below.   To see the new outlook open the US August 19 weather maps (page 2).