MID-SUMMER SLOG...

We are into that time of year when the seasonal jet tends to be at its weakest due to the lack of cold air intrusions from Canada. Some of you are no doubt familiar with the term dog days, a period in mid to late summer when the weather tends to be at its hottest and most unbearable on a consistent basis. You might even say, it's not fit for a dog!

Wednesday was one of those days with a decided "bark" to it, thanks to heat index values of 101 to 107. However, we were able to put it behind us relatively fast Thursday thanks to a decaying line of storms that dumped heavy rain just NW of my area. Those storms fell apart before they could impact my area with any rain. Even so, they were a substantial force, producing an outflow boundary that impacted the majority of my area Thursday. For those who don't know, an outflow boundary is the leading edge of rain cooled air that's pushed out of a thunderstorm complex by way of downdrafts. They act like mini cold fronts and in this case the outflow boundary significantly tempered the atmospheres potential to heat up due to debris clouds and rain cooled air.

I anticipated such a development over my NW counties and accounted for far less heat in that part of my area Thursday. What's hard to know is just how far the outflow boundary can progress before it washes out. The general idea was that it would reach the Quad Cities and stall, leaving my counties in SE Iowa and WC Illinois vulnerable to another blistering day. In general that was the case, although the outflow over-performed and the only place that reached the 100 degree threshold necessary for a heat advisory was Macomb, located on the southern fringe of my area. These are the peak heat index values around 3:00pm, much lower than 24 hours earlier.

With the outflow boundary stalling well south of my area, new thunderstorms erupted along it Thursday evening, some grazing SE Iowa and WC Illinois. The more intense storms were found further south in Missouri and central Illinois, as you can see in this radar image snapped around 9:00pm Thursday evening.

Up in my northern counties around Dubuque, the skies were clearing, and it was actually a pretty nice evening. I took this picture from my deck of this exceptional sunset over the Mississippi.

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MORE STORMS & HEAT...

Over the next 5 days, the 500mb jet stream pattern is projected to look like this around North America. You will notice that a heat ridge over the east is shown retrograding west towards the Midwest. My area remains on the northern edge of the heat dome, in the place known as the "ring of fire". That keeps our weather very warm, humid, and stormy at times. Friday, with passing clouds and a few scattered showers and storms, especially in the south, temperatures should remain close to 80, actually below normal. After that, the ridge begins to build and temperatures and humidity will steadily climb, reaching the 90s once again Monday.

Highs in the 90s will be bad enough, but look at what the EURO shows for low level moisture Monday, dew points as high as the low 80s, some reaching 83 degrees. That's in the top 99% of climatology

The combination of heat and moisture will be volatile and could produce heat index values areawide in the range of 103 to 116 if the EURO is correct. Heat headlines will most likely be needed, perhaps reaching warning criteria.

Tuesday has the potential to be nearly as sizzling as Monday, especially over the south. I don't see much relief until a front arrives Tuesday night with thunderstorms and much cooler air for the middle of next week.

Leading up to that, there will be no shortage of moisture, with available water vapor late Friday night well over the 2-inch mark.

With a diffuse front and outflow boundaries around, showers and storms are likely to be scattered around parts of the region Friday and Saturday. Friday, the south would have the best chances, but even there, subsidence suggests minimal coverage during the day. With time, opportunities should shift northward to involve all but my far northern counties. An MCS is even possible in some areas late Friday night and early Saturday, with the potential to produce heavy rain across the south with such high levels of water vapor. Sunday, with the expansion of the heat dome, rain chances look lower, although some spotty storms are still possible. Monday, despite extreme instability with CAPE shown at 6,000 j/kg, very warm air aloft provides a stout CAP which thwarts thunderstorm development and provides searing heat and humidity.

Tuesday has the makings of another scorching day, but the arrival of a healthy cold front should provide storm chances Tuesday night, followed by much cooler conditions the middle of next week. Here's what models are suggesting for rain totals through Saturday night. Notice the emphasis on the bulk of the heavier rains over the southern half of my area.

The EURO

The GFS

The 3k NAM

The HRRR

In essence, what we've been seeing lately is what we'll continue to witness into next Tuesday. Lots of heat, abundant humidity, and scattered storms. The mid-summer slog continues in earnest. Happy Friday everyone and roll weather...TS