A change is coming in the central United States weather pattern. Yes, we have officially entered spring, as of March 19, as the Earth passed the Vernal Equinox, bringing more hours of light than darkness to the Northern Hemisphere. Springtime is a season of change. Average temperatures rise, precipitation is more likely to be rain than snow, and plants break dormancy. The U.S. has been stuck in a relatively stagnant pattern for a while now, with a storm track from the Plains through the Midwest. If models are correct, that could change starting next week.
Previously, the pattern has been rather stagnant with a trough in the west or off the West Coast, and a ridge in the southeastern U.S. This sets up a consistent storm track from the Southern Plains through the Delta and southern Midwest. Precipitation in these areas is running well above normal with widespread recordings of 5 to 8 inches of rainfall over the last two weeks. The pattern continues for this week and another couple of storms could produce some moderate-to-locally heavy rainfall. But that may be changing, at least for a little while.
Forecast models are suggesting that the trough that moves through the interior of the U.S. March 27-29 could be the last of the series of colder storm systems, followed by upper-atmosphere high pressure (ridge) building into the west and central states for the start of April. This is not to say that the spigot will shut off completely. Weaker disturbances in the jet stream may still produce some rain events. But the likelihood is that these systems will be weaker and more scattered. Also, the storm track is more likely to be over the Gulf Coast, which needs rain. That is particularly true in Florida where the peninsula has seen almost no precipitation in the last two weeks and less than 1 inch in the last month.
The result of this new pattern is below normal precipitation for most of the growing areas with an increase over the south for the period of March 29 through April 2. This outlook is based on the European model ensemble. This could be enough time for soils to dry out enough to get fieldwork back on track ahead of spring planting.
Not all models agree. The U.S. GFS model is not as dry as its European counterpart, and even the operational run of the European is wetter than its ensemble indicates. But the pattern presented is roughly the same. The differences come in how these models treat the weaker disturbances that move through. So while there is an indication that the overall pattern change could be toward a drier and warmer scenario for the start of April, minor disturbances could throw a wrench into the outlook.
In South America, Brazil continues to see showers over its northern zones that have generally finished planting second crop corn and cotton. These showers will help with emergence and establishment of these crops. It is a mixed bag of precipitation over central areas. Scattered showers are missing some areas and are becoming too dry. Others are having enough rainfall for their newly planted crops. But over the south, dry conditions are mounting. Even with widespread rainfall over this past weekend, soils have only seen about 20-40% of their normal precipitation over the last 60 days. This dryness is having an adverse impact on full-season corn and soybeans that have yet to be harvested.
Argentina continues to have concerns over adequate moisture. After another dry weekend, showers will be moderate during midweek in the central and southern growing areas. Rainfall may persist in bands and could exceed 30 millimeters (around 1 inch) of accumulation. The area also looks to have a few chances at meaningful precipitation over the next week.
John Baranick can be reached at firstname.lastname@example.org
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