CAUSE AND EFFECT...

The weather pattern Monday was a mish mash of boundaries that included a warm front in the north, a diagonally positioned cool front, and an assortment of outflow boundaries, (little baby fronts that are the remnants of rain cooled air). None of these were particularly strong or moving much. However, they were strong enough (to cause) hit-and-miss pockets of rain, which in turn were the end (effect). Most of what fell in the north was early in the day, the majority of what occurred in the south came later in the afternoon. These are Doppler estimates of how much fell. A few spots in green picked up 1/2 inch, but in general amounts were 1–2 tenths of an inch or less.

Despite most areas seeing some rain, there were plenty of dry hours and enough sunshine to produce highs in the 70s across the board. In fact, it was a fine afternoon at my place and the yard was mowed for the first time all year. Now I have that chore to look forward to for at least the next 6 months. The price you pay for warm weather.

From the looks of things, weak boundaries (some related to fronts, others to outflow) will continue to be aligned across the central Midwest through the end of the week. It's expected to create enough differential heating and forcing to produce additional showers and some storms into Friday. In this type of set-up, they can be a bit difficult to time and pinpoint. About all you can do is broad brush the threat and play it day by day.

Overnight, the low level jet has already generated rains that have been substantial in narrow bands of convection between I-80 and HWY 30, as well as parts of SE Iowa and WC Illinois. Some amounts of 1–2 inches may have fallen.

Wednesday, any rain ends early in the south, with the threat shifting more towards the north. Even there, it should dissipate by early afternoon. There will be plenty of dry hours that allow highs to again reach the low 70s north to the mid to upper 70s south.

Thursday I expect similar temperatures, but the shower and storm chances appear confined to the far north, closer to any boundaries. Thus, most areas will end up with a warm late April day, with an 80 possible in the south. The HRRR indicates this for highs Thursday.

The most organized chances for rain appear to come later Thursday night or Friday morning, when a disturbance rides the ridge into the region. Some modeling is hinting at the potential for an MCS (mesoscale convective system) in some part of my area. If timing is appropriate, it may bring a couple of stronger storms and some localized heavy rains.

Precipitable water vapor hovers near an inch or more meaning where any thunderstorms can develop, they have the potential of producing some brief but heavy downpours anytime between Wednesday and Friday morning. Moisture levels are at their maximum Thursday night, with PWATS on the EURO at 1.20 to 1.40 inches. That's about twice what's normal.

Between now and Friday at noon, here's what models are suggesting for rainfall. There is a trend currently for my western and southern counties to see the more significant rains.

The EURO

The GFS

The 10K GEM

The 12K NAM

Friday morning showers advance out of the area in the morning with winds turning to the northeast thanks to a back door cold front. This provides the region with Lake Michigan enhanced cooling and a notable change to much cooler temperatures. Highs will start in the 60s, but by late afternoon should sink into the 50s, especially in the northeast.

Strong cold air advection settles over the region Friday night and Saturday, allowing the weekend to get off to a rather fresh start, with lows on Saturday clipping the upper 30s up north. Low 40s are expected elsewhere. Wind chills around daybreak will range from the low 30s north to mid 30s south. Very frisky! Lows on the GFS.

Eventually, highs Saturday should reach 60-65. Sunday, return flow and sunshine will give temperatures a boost, sending them into the range of 68 to 74 Sunday. A nice way to close out the weekend.

Early next week, (as Nick was suggesting a few days ago), looks interesting for some part of the region in terms of a severe thunderstorm risk. Warm air, substantial moisture, and a healthy short wave point to the major ingredients driving the storm potential. SPC already has a slight risk for day 7 in place, which indicates a high degree of confidence on their part a week in advance. Later Monday or perhaps even Tuesday is when my local area could be impacted. Something to put on the back burner. Lots can change between now and then.

That's a wrap for now. Have a strong day and roll weather...TS