By John Nyaradi

The Midwest remains under a record heat wave, sending shock waves through agricultural commodities.

Supplies are threatened and crop failure is being discussed as summer wears on.  June was the fourth-hottest month ever, according to the National Oceanic and Atmospheric Association.

Most analysts forecast higher prices, as the drought is expected to continue into late July. Soybeans have reached record highs, and corn is also near a record high on commodity futures exchanges.

PowerShares DB Agriculture ETF (DBA) was up 3% last week. The ETF tracks the Deutsche Bank Liquid Commodity Index -- Optimum Yield Agriculture Excess Return and its components include corn, wheat, sugar and soybeans

Tecrium Corn ETF (CORN) added 4.2% for the week. This ETF tracks the closing prices of three corn futures contracts on the CBOT

Tecrium Soybean ETF (SOYB) rose 4.9% last week. The ETF tracks the weighted average of the closing settlement prices for the three soybean futures contracts.

Overall, ETF prices have seen sharp rises with PowerShares Agriculture ETF up 17% since June 4, Tecrium Corn advancing 41% since mid-June and Tecrium Soybean ETF up 23% since June 1.

Bottom line

Profit opportunities could be ahead for agriculture ETFs, but the sector will be volatile and completely weather dependent. Investors and traders need to be nimble and able to respond quickly to changing market conditions.

John Nyaradi is Publisher of Wall Street Sector Selector and author of the book "Super Sectors: How to Outsmart the Market Using Sector Rotation and ETFs." His articles have appeared in Market Watch, and Yahoo Finance among others. Follow him on Twitter @WSSectorSelect