ERRATIC AS FLIES AT A PICNIC...

August 2, 2017

Summer rains are as erratic as flies at a picnic. They come and go and can be just as irritating, drenching some and bypassing others. It's always a trick to get the right amount at the appropriate time, just ask a farmer...it's something they've learned to live with.

 

This summer is an excellent example of just how extreme rains can be over a very short distance. Look at this graphic showing July rainfall. It goes from top 3 all-time wetness in SW Wisconsin to top 9 all-time dryness in south-central Iowa...a distance of less than 200 miles. The data is based on 125 years of records.

In my viewing area alone, rainfall varied from 14.28" in Guttenberg to 0.74" in Sigourney. A range of 13.54" in 150 miles. That's the difference between severe flooding and significant drought.

On the topic of drought, a small part of south-central Iowa is classified as being in severe drought conditions. All told, 64% of the state is considered abnormally dry.

The next chance of rain comes Wednesday into Thursday along a vigorous summer cold front. The timing of the front will hold the key to how much rain falls and precisely where.

 

Any rain that falls Wednesday looks spotty and tied to a weak wind shift line that washes out over southern Iowa. Coverage looks to be on the order of 20-30%, that's if the convective temperature can even be reached.

 

Later Wednesday night and Thursday the true cold front makes its move and that's when a more organized chance of storms exists. Even so, the clusters look broken and forcing is not particularly strong. Most rain totals in my area should be light to moderate at best. The EURO has this for rainfall through Friday. The heaviest up north in Minnesota and Wisconsin. More bad news for the drought areas.

Once this disturbance gets out of the Midwest a very pronounced and unseasonal NW flow sets up for the long term period. You can see the very low 500mb heights the GFS is forecasting next Tuesday.

The cool air will engulf much of the U. S. east of the Rockies. Just look at this remarkable 10 day temperature departure the CFSv2 is showing for the period August 1-10th. Wow!

 

Even the GFS which is often warm biased is sensing the cool air by the weekend. It has this for highs the next 10 days...8 consecutive 70s. Pretty impressive for the dog days of summer!

For those of you who like fall, get ready for a legit preview this weekend. That's a wrap for now. Until next time roll weather...TS

 

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© 2019 Terry Swails