The US is poised for yet more of the rainfall, while boosting potential for row crop yields, are undermining barley and wheat condition, spurring worldwide concerns over the availability of quality supplies.
The spring wheat belt running from the northern US Plains into Canada's Prairies is poised for more rainfall this week which, while not expected on the same extent as last week, will continue to interrupt an already-slow harvest.
"Heavy weekend rains in key areas of North American spring wheat and durum production will limit harvest progress early this week," said Brian Henry at Benson Quinn Commodities, based in Minnesota, a big US spring wheat-growing state.
"The potential for additional rain is noted this week and current forecasts indicate the potential for heavier amounts into next week."
In Chicago, Terry Reilly at Futures International said that "the harvest of the spring wheat crop has been largely put on hold, and rain late in the week will again interrupt harvesting".
US Department of Agriculture data overnight showed the US spring wheat harvest only 27% completed as of Sunday, below an average of 49% by then.
In North Dakota, the top spring wheat growing state, just 10% of the crop was in the barn, compared with a typical 34% by now.
"Heavy rainfall last week halted small grain harvest," USDA scouts said.
"Almost the entire state received at least an inch of moisture last week, with areas in the southwest reporting totals of 4-5 inches."
In South Dakota, where the harvest was 30 points behind the typical 87%, "rain and humid conditions across South Dakota slowed small grain harvest".
And in Minnesota, where growers have only 12% of spring wheat in the barn compared with an average of 66%, "widespread rains in slowed small grains harvesting".
Furthermore, the rainfall has threatened quality too, at a time when harvest-time rains have already damaged much of the European Union harvest, expected by Strategie Grains to show an unusually low proportion of wheat fit for milling, with talk too of depressed protein levels in Russia's crop.
The proportion of US spring wheat deemed "good" or "excellent" dropped 2 points to 66%, falling below last year's reading too.
Mr Reilly said: "US quality problems are starting to raise concerns, leaving some wonder if supplies of high protein wheat will be ample enough throughout the 2014-15 season."
The results of Australia's harvest, not expected to start for another couple of months, "will be important this year" in determining world supplies of quality wheat.
The decline in US spring wheat quality was particularly severe in Idaho, where the proportion of spring wheat rated good or excellent tumbled by 12 points to 37%, thanks to rains which reached "extreme levels" in some areas.
"Throughout the state there were reports of mould damage in wheat and alfalfa," USDA scouts said, flagging too reports that, in barley, "premature sprouting has degraded the quality from malting capabilities to feed-only grade.
"Extreme weather conditions have increased concern of economic losses for cereals, alfalfa, and beans."
However, the rainfall has, broadly, been positive for row crop condition, helping the proportion of US corn rated good or excellent rise 1 point last week to 73%, the best rating for the time of year since at least 1993.
Condition improved in states including Minnesota, where USDA scouts said that the rains which delayed harvesting "helped improve row crop and pasture conditions".
Similarly in North Dakota, scouts said that the heavy rains "were needed for row crop development".
In South Dakota, "above-average temperatures in the east aided row crop development".
The proportion of US soybeans rated good or excellent fell 1 point last week but, at 70%, was also the highest since at least 1993.