In a stark reversal from Easter weekend, temperatures have moderated and gone below normal for a large portion of the Plains and into the Midwest as of April 13. Sometimes Mother Nature needs to remind us that spring is a time of variability; and, just because it was warm most of March and early April, conditions can go the other way, too.
Winter wheat progress is moving into more vulnerable phases. The Kansas winter wheat crop is 29% jointed as of April 12, seven points behind the five-year average 36%. The Colorado crop is 19% jointed, eight points ahead of the average 11%. It is at this point that we start to worry more about temperatures getting below the freezing mark. As wheat starts to joint, temperatures that dip into the mid-20s Fahrenheit for a minimum of two hours can result in moderate to severe impact on yield. The Colorado crop is ahead of average at 19% jointed.
Here is the mechanism which is producing this sharp cooldown: Upper-level lows have been cut off from the main atmospheric flow as a ridge has developed over the top of them, stalling them in the Midwest and West. A trough of low pressure will force the ridge to split both east and west, eventually setting up a ridge in the western half of North America, and a deep trough across the eastern half. This scenario will likely remain in place through next week.
The trough will allow cooler air from northern Canada to flow south through the Plains and Midwest. The largest push of this cold air appears to come early next week across the northern tier of the country; but the coldest air for the western High Plains actually comes this weekend, behind the departing upper-level low currently over the West. Both waves of cold will have chances to bring low temperatures below freezing and into the 20s F.
The European forecast model currently suggests that low temperatures will be in the middle to upper 20s over western Kansas, Colorado, and the northern Texas Panhandle this weekend, and again over Colorado, Nebraska, and Kansas and points northward during the first half of the April 18-to-April 24 week. Winter wheat in these areas will be at risk for some frost damage, especially in Kansas and Colorado where wheat is likely more advanced.
Corn planted early in the Midwest may be at some frost risk depending on its progress. Low temperatures may not make it into the 20s F this week, but they might next week. The same European model also indicates sub-freezing temperatures in at least Iowa and northern Illinois early next week. Meanwhile, the temperature may reach down to 30-32 F in several other spots around the Midwest.
Iowa, Illinois, Indiana, Michigan, and Ohio have already reported corn planting progress on the latest NASS weekly report. If germination occurs before the colder air moves out, there could be frost damage.
Climatologically, frosts are typical through much of the Midwest through the end of April and for the northern and far eastern Midwest into May, making these early plantings a bit risky, especially if the potential for cold were to stick around for an additional week.
A beneficial item that is arising out of this pattern change is moderate precipitation in the far Northern Plains. North Dakota, the nation's leading spring wheat producer, has seen drought continually increase since last summer. Moderate precipitation fell as one of the upper-level lows moved through over this past weekend, and the showers continued through April 13 before waning.
Precipitation has fallen mostly as snow with around 0.50 inch of liquid equivalent and some locally higher amounts. It is not enough to reverse the drought by any means, but it should provide some beneficial soil moisture when it melts. With temperatures being below normal for the next 10 days at least, that melting will be slow, providing better infiltration into the soil profile rather than running off into local streams and rivers.
Another aspect to the current pattern developing will be increasing temperatures and overall dryness in the Pacific Northwest. The wheat crop rated good to excellent in Idaho and Oregon fell by 8 and 4 percentage points, respectively, during the last week. These were places that saw below-normal snowfall in the mountains during the winter and may be a little more reliant on springtime precipitation to supplement the lesser snowmelt. The heat and dryness may cause plants to advance more rapidly and if moisture does not follow, could cause stress. There does not seem to be much help as systems are looking to mostly go around the region.
John Baranick can be reached at firstname.lastname@example.org
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