THE TIDE HAS TURNED...

After two months of active weather featuring an abundance of heat, humidity, and rain, the tide has turned. The breakdown of a persistent heat dome has changed the 500mb jet stream flow to the northwest. The atmospheric realignment is now restricting moisture and heat, and the end result has been the sudden realization that summer is winding down.

In the animation below, you can see the trough that's brought widespread 40s the past couple of mornings briefly breaking down and shifting east, only to be replaced by another strong trough come the start of September. In general, the end result is a continuation of below normal temperatures and precipitation through the first week of September.

These are the average 10-day temperature departures indicated on the EURO for the period ending September 5th. That's a major reversal from what we've been experiencing since late June.

Average 10 day precipitation is also well below normal on the EURO for the same period. Again, a big turn around from the wetness of July and the first half of August.

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CHILLY WILLY...

Stepping back for a minute, it's worth revisiting the lows experienced around the Midwest Tuesday morning. My entire area was in the 40s, generally a degree or two from breaking records. Close but no cigar. Rochelle, Illinois dropped to 40 while Land O Lakes and Tomahawk, Wisconsin dipped to 35!

Wednesday morning will get off to another fresh start with readings a few degrees warmer with return flow developing as the core of the current cool air mass drifts off to the east. Later in the day, an upper air disturbance will approach from the NW. It will be starved for moisture, but could provide enough forcing and warm air advection for a few showers or isolated thundershowers in the afternoon or evening. The rains look more substantial in NC Iowa as they peak around midday. At that time they reach my western counties where they encounter substantially drier air which promotes a weakening trend of whatever rain can survive, and only light showers or sprinkles are expected in my local area. My counties north of I-80 and west of the Mississippi have the best chance of seeing and showers. The south should remain rain free. At best, amounts are expected to be .05" or less. Here's what models indicate for totals.

THE HRRR

The 3k NAM

The EURO

The GFS

Temperatures Wednesday will be tempered by clouds, especially in the northwest, where some spots may not get out of the upper 60s. The south without the rain threat and less in the way of clouds could pop back into the upper 70s. The HRRR shows this for temperatures at 3:00pm.

Thursday, a cold front associated with the system sweeps south in the morning. Despite some forcing, dry air is likely going to limit any rain chances and a dry frontal passage is expected. Later in the day, the north could get into some post frontal showers, due largely to instability driven by cooler air aloft in northeasterly flow. Thursday is still expected to be the warmest day of the week and upcoming weekend, with highs of 75 to 80.

THE HOLIDAY WEEKEND...

After that, high pressure builds into the Great Lakes over the weekend. That will bring another punch of cool air with E/NE winds delivering a fresh round of cool dry air. That keeps the weekend nice and comfortable, with mild days and cool nights. It also forces any respectable moisture well to the west and south, where the active storm track will reside. That keeps us high and dry through Sunday and most likely Labor Day as well. The GFS Meteogram for the Quad Cities shows this for temperatures through September 8th. Only one of the next 13 days is shown reaching 80 with the remainder well below normal in the low to mid 70s. Wherefore art thou summer?

After that, there are signs warmer weather will make an attempt to enter the Midwest around September 10th, due to deamplification of the NW flow. Something to keep an eye on. That will do it for now. Happy hump day and roll weather...TS