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It felt like summer Friday with many spots enjoying highs around 80 along with a good deal of humidity. Here and there some showers and storms popped up too, mainly to the north of a warm front draped out across southern Iowa. The mild, muggy conditions will be around again Saturday. Then, a rapid transformation takes place that leads to the potential of heavy rain Saturday night and crashing temperatures Sunday. We'll all be "chilling out" as the weekend comes to a close.

The culprit in this undeserved change of fortunes is a potent upper air low that vividly appears on the hi-res satellite imagery spinning over Nebraska Friday evening.

Ahead of the system, moisture is streaming into the Midwest ahead of the circulation.

One can readily see why with the 500mb jet depiction showing a strong southerly flow aimed at the area.

With the energy centered so far west, that has kept much of the heavier precipitation and adverse weather to the west. Eastern Nebraska had a big tornado day with 40 tornado reports in that region as of Friday night.

Saturday, the system finally opens up and makes a move southeast towards eastern Iowa. The front that's been in the area for a couple days gets reinforced in a NW to SE fashion that places it from NC Iowa to just about the Quad Cities in the early afternoon. While a few showers and storms could be around early Saturday, the main show comes late in the day and overnight when thunderstorms are expected to develop.

As far as severe storms go, the best instability will be near and south of the front (basically the SW half of my area). CAPE and shear would be supportive of a few strong to severe storms late in the day. Hail and strong winds would be the primary concern. SPC does have a slight risk outlook in effect SW of a line from Waterloo to the Quad Cities.

Where shear is maximized along the front the flow could be backed enough for a brief tornado spin up. Right now the threat seems minimal. SPC does indicate a 5% risk within 25 miles of a point.

Any storms that form in the afternoon or evening during peak heating would certainly have a heavy rain potential. Eventually, the outflow from these storms will likely push the boundary even further south Saturday evening where it will pause and await a surface low that ripples along it late Saturday night and Sunday morning. The surface low should initiate a swath of over-running rains that has the potential to produce a secondary wave of heavy rain Saturday night over much of my region north of I-80. Guidance has been indicating 1-2 inch totals in spots. This would not be associated with any severe weather and would occur over a longer period of time than the downpours that could develop in afternoon and evening thunderstorms. Here's what models are suggesting for rainfall Saturday through Sunday evening.



The 3k NAM

The GFS, a further south solution that currently is an outlier.



As for weekend temperatures, Saturday will be another mild and muggy day with highs in the mid 70s NE to the low to mid 80s SW. However, as the stationary front begins to sink south late in the day winds veer to the E/NE in the north and temperatures begin to sharply cool. By daybreak Sunday readings will range from 50 north to the mid to upper 60s south.

Sunday starts cold and rainy across the north with brisk winds making for extremely raw conditions. The cold waters off Lake Michigan will only enhance the chill and the cold and associated showers will sink south during the day. The cold air hits I-80 by noon and will be into Missouri by 5:00pm. Here's what the 3k NAM depicts for temperatures at 1:00pm Sunday. With wind gusts over 30mph and periods of rain, it will be an extremely poor day, especially north of I-80.

For some perspective on just how dramatic the cool-down is, here's the 24 hour temperature changes from 2:00pm Saturday to 2:00pm Sunday. Most of the region is 25-30 degrees cooler. Ouch....

Following a very fresh start Monday morning with readings of 39-43, the day makes a nice recovery thanks to the strong mid-May sun. Highs should get back up around 70 and hold at 70-75 through Wednesday. The next rain chance looks to hold off until Thursday night.

Well, there's a little something for everyone in this forecast. However, in the end the bad of Sunday far outweighs the good of Saturday. Pick your poison as the saying goes. Have a nice weekend and roll weather...TS


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