© 2019 Terry Swails

ANOTHER DAY OF THUNDERSTORMS...

July 26, 2017

The Midwest is well known for its climate diversity. Extremes are as common as the corn fields that ripple in the summer breeze. This year a dramatic extreme has developed across Iowa where a huge rainfall disparity has been noted the past 30 days. The northeast is excessively wet while the southwest is excessively dry and in moderate drought.

 

This is due to a persistent July weather pattern that has baked southwest Iowa in 90 to 100 degree heat capping the atmosphere and thwarting thunderstorm development. Further northeast, the ring of fire has allowed cooler temperatures over NE Iowa and numerous rounds of thunderstorms. Just look at the 3o day rainfall totals. Parts of Clayton County, Iowa have had as much as 20" of rain. Serious flash flooding has resulted in nearly a dozen Iowa counties being declared disaster areas.

As you would expect in that part of Iowa excessively wet soil conditions exist with a moisture surplus of more than 3 inches.

Further south the lack of rain has resulted in drought conditions over the southwest half of the state. It's not often you see such a dramatic contrast over such a small geographic area.

 

Turning to Wednesday, the weather issues of the day will be focused around a cold front that advances across the central Midwest. Ahead of the front warm and very moist air will prevail. In those areas that stay storm free most of the day highs of 85-90 and dew points in the mid to upper 70s will make for a searing day.

 

Eventually thunderstorms will explode later in the day. There is still some discrepancy on the speed of the front and where the storms develop. The GFS is faster and further south with the severe threat and heavy rains keeping them near or even south of I-80. Considering the conditions I just described above this would be great news for the driest areas of Iowa. Here's what the GFS shows for total rain.

Here's a larger perspective.

Some of the hi-res models are further north with the heavier rain getting it more into central Iowa near HWY 30. No way to know until we cross that bridge late Wednesday morning. As it stands now the Storm Prediction Center has this part of the Midwest under a risk. Based on what I've seen this will probably be cut back eliminating parts of northeast Iowa and southern Wisconsin in later outlooks.

Whatever happens Wednesday, it's a certainty that the end of the week and upcoming weekend will be nice around the Midwest. High pressure will be in full control allowing comfortable temperatures and plenty of sunshine. A fine way to close out the month of July. Roll weather...TS 

 

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