KANSAS CITY — After a frustratingly slow start, durum planting across the northern Plains made good progress in the week ended May 12. At the same time, heavy rain across the durum areas of the northern Plains early this week temporarily halted planting as the struggle to seed the 2013 crop continued.

The U.S. Department of Agriculture’s field office in North Dakota indicated durum seeding in the state was 35% completed by May 12, which compared with 3% a week earlier, 91% on the same date last year, when planting was off to a historically early start, and 52% as the recent five-year average for the date. The U.S.D.A. said North Dakota durum wheat was 5% emerged by May 12 compared with 69% in 2012 and 28% as the average for the date.

Montana durum was 39% planted by May 12 compared with 15% a week earlier, 80% last year and 67% as the average for the date.

The only other U.S.D.A. field office to report on durum progress in the latest week was Arizona. The field office there said the condition of the Arizona crop, planted last winter for harvest in the next few weeks, remained in mostly fair to good condition.

Six states grow nearly all of the durum produced in the United States. Durum is planted in the winter in Arizona and California for harvest in late May and June. The rest of the nation’s durum is grown across the northern Plains and in Idaho with North Dakota historically the most important durum state. The northern Plains durum harvest is in the mid-summer with new crop supply in most years not reaching the market in volume until September. Until then, durum mills grind old crop supply.

The U.S.D.A. in its Prospective Plantings report issued at the end of March estimated durum plantings in Arizona and California at 155,000 acres, down 57% from 245,000 acres in 2012 and compared with 200,000 acres in 2011. Durum planting in the “desert states” fell short of the 170,000 acres the U.S.D.A. forecast a couple of months earlier in its Winter Wheat Seedings report.

In its Wheat Outlook issued May 14, the U.S.D.A. forecast durum production in the two desert states at 16 million bus, down from 24 million bus in 2012 because of a smaller projected harvested area that more than offset a forecast for an increase in average yields in 2013.

The U.S.D.A. forecast plantings in the six key states, including the desert states, at 1,751,000 acres, down 18% from 2,123,000 acres in 2012 and compared with 1,369,000 acres in 2011. Plantings in the key state of North Dakota were forecast at 1,100,000 acres, down 18% from 1,340,000 acres in 2012 but up but 47% from 750,000 acres in 2011, a year in which many acres intended for durum went unplanted across the northern Plains because of excessively wet weather in the spring.

The price of choice milling hard amber durum was on the rise despite weakness in the other wheat classes. The Chicago price was between $10.50 to $10.75 a bu. Prices may continue to advance at least in the short term as farmers were planting the new crop and not marketing additional old crop supply.

The U.S.D.A. will provide its first forecasts of harvested area, average yield and production for durum in July.