"Active" continues to be the word used most often when describing the weather patterns this spring. It doesn't seem to matter the configuration; storm systems have continually pushed through North America over the last several months. That is partially due to the above-normal sea surface temperatures in the tropical Pacific which are indicative of an El Nino base state. While those ocean temperatures have been cooling for months and are on the precipice of neutral on the latest update from the Climate Prediction Center, the active storm track has continued regardless.
The latest upper-air setup has featured a ridge in the East and troughs that move into the West and have bombarded the eastern ridge. The clockwise motion around the ridge has brought significant moisture from the Gulf of Mexico northward into the middle of the country. And as those storm systems have moved out of the west, through the Plains and then the Midwest, they have had a lot of energy and moisture to produce areas of heavy rainfall. That has helped reduce the long-standing drought and long-term rainfall deficits but has also brought round after round of severe weather and heavy rain that has produced flooding.
A change in the pattern is upon us this week as one of those troughs finally beats down the eastern ridge. At the same time, a new ridge is forming in the Gulf of Alaska. So instead of a western trough and eastern ridge, our pattern is going to be more indicative of a western ridge and eastern trough, a sort of 180-degree flip in the pattern.
Usually, you would think that would mean opposite weather conditions. Instead of a warm and active pattern, it would induce a cool and dry one. However, that will not be the case with this one. The jet stream is going to split into two as this change occurs, but both jet streams are active ones, with multiple disturbances within the streams to produce more storm systems across the U.S. and Canada.
There will be changes, though. While the northern stream will continue to produce storm systems across Canada and the northern U.S., the source region of these storms will be northwestern Canada, which is a drier region. Storm systems that move through starting this weekend will have less access to moisture and thus be more isolated to scattered showers instead of widespread heavy ones.
They will also be moving at a rather decent clip with less of a chance of severe weather. Recent storm systems have been lingering across some areas for a couple of days at a time. The ones on tap should be more like clippers, moving through rapidly. They may leave behind frontal boundaries that continue to produce showers at times as well, giving the impression of lingering rain, but overall, these systems are going to be moving along quickly.
Across the southern tier of the U.S., the active stream may bring beneficial rain to a lot of areas. This active track starts in the Southern Plains and then works along the Gulf Coast starting Sunday and continuing through much of next week. Two or three of these storms may occur and that could mean widespread showers for the southwestern Plains winter wheat areas that have been very dry this spring. However, that is not guaranteed as the access to the Gulf of Mexico moisture will be limited, occurring more as the systems approach the Gulf. Therefore, heavier rain across the Gulf Coast and Southeast looks more likely. These areas have not been as active as the Plains and Midwest in recent weeks and planting there has gotten off to a very good start. The active pattern here will favor those who have already planted but will likely produce delays for those who haven't. Severe weather will also be more likely with this southern track than the northern one, giving those in the Plains and Midwest a break from the incredibly active severe season thus far.
This double-jet pattern may not last long. Long-range models are suggesting the two combine across the Rockies for the following week, suggestive of more large storm systems for the northern tier while getting quieter across the south. Extended versions of the American GEFS and European ECMWF models both show a similar change taking place that could last well into June.
For those with crops yet to plant, we'll be watching how this active season continues going into summer and whether significant planting delays will last into June, which would set back yields to some degree, even if they have good rainfall throughout the summer months.
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John Baranick can be reached at john.baranick@dtn.com
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