Don't Expect the Wetness of June to Continue

The NWS Hastings prominently documented the impressive near-record rainfall of last month. You can find the summary here. However, the pattern that brought the excessively wet June is gone and the region has transitioned to a much drier pattern. Now, that does not mean that expanding drought is right around the corner, just that the chances for rain will be fewer and farther between, at least through mid-month. It is entirely possible that rainfall totals could end up close to normal (generally 3 to 5 inches from north-to-south, with the greatest amounts over north central KS).

The image below shows the mean jet stream pattern for last month. Note the dip (or "trough") over the western United States. This indicates that the month was dominated by disturbances moving in from the Pacific Ocean. This pattern was also responsible for the very wet June's of 1967, 1968, 1975, 1990, 2008, 2009, and 2010.

Now, much of the numerical weather prediction model guidance we have access to indicates the pattern has switched - from a trough in the West to a Ridge. On the average, this results in less rainfall.

The image below shows, among other things, the flow in the atmosphere at the jet streak level. (Note the pattern of the 1200m and 1220m lines). This is the forecast, from one of the numerical models, for the entire month of July. Notice that the trough is gone from the western U.S. and that a ridge is forecast. The trough is forecast to be over the eastern U.S.

 

 

Below is what this model has forecast for rainfall departures from normal for the month of July. The oranges, reds, and browns indicate less than normal rainfall is forecast.

 

 

This model forecast does resemble the official monthly guidance from the NWS Climate Prediction Center. Because forecasters do not always take numerical model guidance verbatim, the CPC has indicated equal chances for above, near, or below normal rainfall over the Central Plains.

 

This means that irrigation may become necessary very soon.



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