Before I get into the meat of this blog just wanted to say that Saturday night I will be at The Grove Bar and Grill in Scotch Grove, Iowa (just outside Monticello). Carolyn and I will be there to enjoy some good food, a cool beverage, and take in some karaoke. I'll also get to catch up with my friends (and the owners) Brandon and Madalyn Schrader. If you get a chance, stop in and say hello. We'll talk some weather and have a few laughs.
Make no mistake about it, the dog days of summer are here. How quickly time flies. With cold air limited the storm track and pressure patterns tend to be weaker. Without the wrapped up storms of winter, spring, and early summer, rainfall becomes more scattered and sometimes hard to get. The absence of strong fronts makes precipitation more instability driven. That also makes it spotty. While one part of the county may get a good soaking, places a few miles away may not even see a drop.
Such a late summer pattern has evolved the past few weeks as evidenced by the lack of rain in parts of Iowa and Illinois that were drenched during the spring. These are the rain totals over the past week.
Most of Iowa, Illinois, and Indiana have less than half of its average rain for that period. Much of eastern Iowa and western Illinois were under 25 percent with some spots seeing no measurable rain at all.
Since July 1st, a few areas have accumulated deficits greater than 3". Iowa City currently is experiencing its 8th driest July to date with just 0.89" in the bucket.
The next 7 days promise one chance for rain in the areas that could use it across the central Midwest. A front will act as the trigger for scattered showers and storms Sunday night. The Weather Prediction Center has some amounts up to 1/2".
The GFS is even more bullish across the north with totals that look like this.
The EURO is far less impressed with the system producing lower rainfall totals.
The NAM is also in the camp of the EURO.
Several factors will come into play in determining the final outcome. For example, how much moisture pools ahead of the front and what time of day it passes will be critical The lower the moisture, the lower the amounts. The more instability, the better the chances of strong storms and updrafts that can dump heavier rains. An evening frontal passage is best as it can off-set capping yet still tap into the instability that exists from the days heating.
As I mentioned above, without a strong thermal gradient and surface low, storms in this type of environment can be hit and miss in nature. What would be best is a solid line of storms without gaps that lead to spotty totals.
While there is no way to know for sure how these key variables will play out, I am concerned amounts will end up more in the conservative side like the EURO and NAM depict. If you're looking for rain, I would employ cautious optimism in this particular case. We'll know soon enough.